Author: Samuel M. Goldwasser
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Copyright © 1994-2004
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Mostly, you will learn by doing. However, you do need to prepare.
There are many schools dedicated to electronics repair. Some of these are quite good. Many are not. This document, however, is written from the perspective of the motivated do-it-yourselfer, hobbiest, and tinkerer.
The Repair FAQs usually list suggested references for each area. Your local public or university library will probably have some of these or other repair oriented electronics books.
Above all read and understand the document: Safety Guidelines for High Voltage and/or Line Powered Equipment. Your life may depend on it. That fabulous large screen won't be of much use to you if you are dead.
Collect broken electronics and appliances from your friends, relatives, the dump, garage sales and flea markets, etc. Start on those that have been written off - you will screw up at first. We all did. As times passes, your batting average will improve. It may not happen overnight but it will happen if you apply yourself. There will be many relatively easy successes but the 'tough dogs' may make up for these triumphs. Don't let them get to you - not everything can be repaired. Sometimes, the basic design is flawed or someone before you messed up royally. Troubleshooting is like being a detective but at least the device is generally not out to deceive you.
Experience will be your most useful companion.
If you go into the profession, you will obtain or have access to a variety of tech tips databases. These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.
While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.
As always, when you get stuck, the sci.electronics.repair newsgroup will still exist!
Here's how I see it:
By all means, do what you can to understand basic principles first. Your success will be much more likely when you understand how a device works. If you can, read Electronics Now and Popular Electronics, as well as Nuts and Volts (http://www.nutsvolts.com). Also have a look at the Radio Amateur's Handbook.
These periodicals are not carefully edited, unfortunately, and now and then things get into print that are simply wrong or misleading, but they are still useful; I learned quite a bit from their predecessors (Radio Craft and Radio News!).
I can't speak firsthand, but it might be a very good idea to become (eventually) a Certified Electronic Technician. Look up the I.S.C.E.T.
Hearsay and folklore sometimes indicate that you should replace a given part when certain symptoms occur, and in the case of frequent failures of such parts, this information might even be true. But that's no way to become a competent technician.
My personal take is that you have to know when to 'let go' of an hypothesis about what the cause of the trouble is. A tech. who persists beyond a certain point in his belief that such-and-such is causing the problem is stuck and spinning his wheels. (I'm sexist; I think women are far less likely to get stuck this way! I think it's a male trait. :)
Troubleshooting is a special field of knowledge and has its own special outlook on things. The device did work, after all.
Production testing and troubleshooting is different; you are likely to be the first person to apply power to a device, and the device has never worked before. If the assemblers aren't giving you excellent quality, you can have some remarkably-bizarre symptoms with a poorly laid-out board from solder shorts, for instance.
A variable toroidal autotransformer (universally known by what used to be a General Radio trade-name, Variac) is priceless for troubleshooting circuits that handle any amount of power and which are powered by the AC line. (Not all devices function at all at, say, half of rated AC input; I work on a poorly-designed amplifier that draws many amps at something like 70 volts with no signal and no load. Unfortunately, Variacs and their equivalents are horribly expensive, at least from some sources! If you get a used one, see that the contact area of the winding is undamaged; you might need to remove a knob and some covers to see it. If the knob is stiff, try some contact/control cleaner/lube; it did wonders for mine!
Learn how to operate a 'scope, and learn why you see what you do. I suspect that some techs are not too well-informed about what goes on inside a 'scope; learn from reliable sources!
Learn to use a digital multimeter, and an analog one as well; the latter is easily damaged if you don't know what you're doing, but it's a great trend indicator.
Learn to use a function generator, and use the triangle output as well! Nothing like a triangle to show a wee bit of clipping or limiting in an amplifier...
Learn how to solder! Solder is not an adhesive; it's a metallurgical bond, according to some sources I trust. It just about has to be with gold, at least! If you *really* want to learn soldering, NASA has developed training courses that will make you a disgustingly good solderer.
(From: Phillip R. Cline (firstname.lastname@example.org).)
I used to repair consumer electronics from VERY high end stereos down to lowly boom boxes. When repairing stereos there is no substitute for good troubleshooting techniques which come from empirical means. Good knowledge of circuit functions helps a great deal. VCRs are almost always a mechanical problem (70% or more in my experience). Audio stuff can be destroyed by the user and often times the design is just plain crap. All low and mid-fi Japanese stuff made within the last ten years isn't worth a crap from a design standpoint. Even a lot of the high-end stuff is junk. They have 71 volt rated caps running at 69 volts etc.... US and most European stuff is way better designed! There are exceptions. I once saw a Philips amp that had a transformer for the power amp supply that wasn't centertapped yet the supply was bipolar. They just rectified and filtered the AC with series caps and the common was the point they were connected to each other. This is fine if you rate the caps at more voltage than the power supply can deliver but these were rated at just over half the total voltage of the supply from rail to rail. One cap shorted and the other one exploded and launched the can sideways across the component side of the amp PC board. This basically did a nice job of depopulating the board along the ballistic path of the cap's can. I laughed for a good while after seeing this.
I gave up repairing stuff when the customers asked, and rightly so, why it costs $80 to fix something that costs $100 new. The OEM parts cost on some stuff was intended to make the customer go buy a new unit instead of repairing the old one. This basically made most of the stuff disposable.
My background was and still is as an electronic hobbiest so the theory of operation was not a big deal and circuit function wasn't either. I have a brother that was the person from whom I learned a great deal of what I know now about electronics.
Soldering ability cannot be overstressed in importance especially with SMT being very common nowadays. As for the guys that seem to be ripping you off in their pricing, they could be gouging you but most often the overhead in the shop and their cost on parts is the most likely cause of high pricing. While labor might seem high a great deal of repair can be accomplished in an hour by a competent technician and some shops have a flat rate for a given repair. This can work to the benefit of the shop sometimes and to the customer sometimes. Our shop was this way. We had the lowest pricing in town(Indianapolis) and the customers still bitched. Sometimes they would take their units after we gave them the price for labor and a estimate of parts cost. We didn't charge for estimates. They would storm out only to come back with their tail between their legs in a few days after checking around for labor charges elsewhere. Depending on their attitude we might go ahead with the repair. Often times we would decline by telling the customer that the other shops may have done something while checking the unit out.(This depended on the shop that the customer took the unit to.) Some of these places had some real winners for techs!! We really didn't feel like undoing some yoyo's handiwork just to get the unit back to it's original nonworking state!
An EE in electronics is useless by itself and will cause a lot of undue troubleshooting to the beginning tech. They will overlook the obvious easy stuff for some possible but unlikely fault. A few years of repairs under their belt though and they can find the most difficult electronic problems with relative ease.
The best way to become proficient is with hands-on training under an experienced tech. A good overall background in electronics doesn't hurt either.
(From: Michael Black (blackm00@CAM.ORG).)
I think one of the problems of home repair is fear. If you're willing to spend the money to have something repaired, then you may think that if you fiddled with it you may make it worse. On the other hand, if you are about to throw something out because it doesn't work, you have nothing to lose by playing around with it and trying to fix it. Or find some stuff other people have thrown out, and start with that.
You may not fix it, but your willingness to open the cover allows you a familiarity that you won't get from a book. You de-mistify the equipment, and by actually adjusting things and seeing the results, you will learn.
I picked up a VCR for cheap at a garage sale this past summer. I was buying it as a tuner for use with a monitor. The guy said it "must be the power supply because it keeps turning off". Actually, it kept turning off because the mechanics weren't working properly. By moving the parts by hand, I saw how they were supposed to work. With the first hand experience, the S.E.R FAQ made more sense than if I'd just read it first, and so did a book on VCR repair that I took out of the library. I saw that the belts needed replacing because I'd figured out how things were supposed to work, and saw that they weren't working that way.
(From: Malcolm MacArthur (email@example.com).)
I have two years' of an Electronic Engineering degree behind me (I gave up on the degree and became a computer programmer. ;) It has been little, if any, help. What you really need is experience... which you'll only gain by fiddling with things. I've been doing repairs since about age 13. After twelve years, I now have a fair success rate, but those first few years were not easy. Best thing to do is get hold of old equipment and just have a go with it (Beware of CRTs, though ;). Be warned, you may break quite a lot of stuff initially! But as the others have said, most of the problems are due to mechanical failures (including dry solder joints).
Tall repair stories time:
"Why bother with repair of VCRs (or anything else) when I can buy a new model for $79.95?"
Actually, I've seen prices as low as $39.95 for a promotion (but not requiring the purchase of anything else)!
"This stuff may have been useful 5 years ago but now some/much of the material doesn't apply to newer VCRs."
While both of these deal with VCRs, it should be understood that it applies equally well to much other consumer electronics.
Depending on your background and interests, these statements may have some validity. Thus, the need for some objective (if possible) way of making a decision as to whether to bother at all, and whether to attempt the repair yourself.
So, when does it make sense to attempt *any* repair yourself rather than to toss the item in the trash or take it to a professional? People do this sort of stuff for several reasons:
It's quite difficult to suggest an approach in deciding when something is worth repairing. You have to decide how much the equipment is worth to *you* in terms of monetary, sentimental, or other value; how much time you are willing to put into a repair; and whether the failure represents a good excuse to upgrade! To what extent each of the factors is significant will also be determined by how much you enjoy troubleshooting and tinkering. If you'd rather be doing something else or keep thinking about all the time you are spending on this rather than something you can charge for, perhaps you should be doing that something else.
However, it is easier to identify specific situations where equipment probably *isn't* worth attempting to repair on your own (or possibly at all):
Where any of these are covered by insurance, that is the best option where the settlement is at all reasonable. If the insurance company allows you to keep the damaged equipment, there is nothing to stop you from attempting repairs as a challenge - you may get lucky. But, it could also be a long drawn out and expensive frustration.
In the good old days when life and electronics were simpler and you could count the total number of transistors in a TV on your hands and feet, service information was included with the equipment or was readily available either from the manufacturer or Sams Technical Publishing (formerly Howard Sams) as Sams' Photofacts (no relation to me). There are still Sams' Photofacts for many TVs at least, but for anything else, obtaining schematics may be impossible or even if they are available, the cost may be excessive. Paying $100 for a mediocre copy of a service manual for a computer monitor that can be replaced for $250 may not be justified.
One way to get an idea of your chances of success for popular brands and models is to search the archives of the USENET newsgroup sci.electronics.repair via Google Groups (formerly Deja.com/Dejanews. There are other public USENET archives but even though this archive keeps changing its name, I see little reason to use others which may come and go and provide less reliable coverage.) Where others have experienced - and repaired - similar problems, your chances of success are greatly increased. Then, if you have detailed symptoms, asking for suggestions on that newsgroup may also be beneficial, especially if you have already done some initial testing. If, on the other hand, the consensus from the newsgroup is that your problem is hopeless, then you may be able to save a lot of time and frustration by giving up immediately (or at least postponing your efforts until you have more experience.
What about older equipment?:
The basic technology of TVs and VCRs hasn't changed significantly in 10 or 15 years. Yes, there are convenience features like "auto clock set" which are supposed to make life easier but often don't (if the station transmitting the clock information has their clocks set wrong or uses a feed from a source in a different time zone!). But as far as picture and sound quality, that VCR from 10 years ago will be just as good or better than one purchased today. Any, it will almost certainly be better constructed and more maintainable.
For example, Panasonic VCRs from the mid to late '80s were solid machines that could be kept in shape with a bit of periodic maintenance (cleaning, rubber parts replacement) and repair of known problems (failed electrolytic capacitors in the power supply after 10 years or so). One could not expect that $39.95 special to provide such service. If it lasts through the warranty period, you're probably ahead of the game. I'd still take a middle age Panasonic over any new low to medium priced model. And, even the high-end VCRs may be based on flimsy chassis.
Here are 4 examples of equipment that I did eventually repair but where serious consideration should have been given to the dumpster. The following can be found described in more detail at in the document: Sam's Repair Briefs/
This TV had taken a nose dive off of a 4 foot shelf onto an unknown surface. And, of course, someone had probably attempted to operate after this with possible additional damage. While the exterior didn't show any major abuse, it was obvious that there was severe trauma as soon as the back was removed. The main circuit board was broken near the (heavy) flyback transformer. Several dozen traces were severed including some to surface mount parts.
A repair shop would be unlikely to want to tackle this for several reasons: (1) the obvious repairs to circuit board traces would take a couple hours at least, (2) there could be unseen damage to the CRT in form of a distorted shadow mask and this wouldn't be known until the circuit board was fixed, and (3) any repair might not catch everything so future problems could develop.
As it turned out, the only damage was to the circuit board and after 2 or 3 hours of soldering - and then finding additional traces to solder - the set was fixed, and has continued to operate reliably for several years.
In the early 1980s, some brilliant manufacturing engineer working for GE decided that a good way to save money on circuit boards would be to use what were dubbed 'rivlets' instead of actual plated through holes to connect top and bottom. A rivlet is basically a rivet which, the theory goes, is then soldered to the copper traces. That's the theory. In practice, due to the thermal mass of the rivet, soldering was never reliable. And, as a result of thermal cycling, cracks developed between the rivet and traces over time. Problems ranged from a dead set to loss of color depending on which rivlet happened to be unhappy on any given day.
Attempting to repair just the problem rivlets was impossible because as soon as you found a bad one and soldered it, another in its vicinity would decide to fail. The only approach that worked was to reheat every one that could be located using a soldering gun. Since there were many dozens of these on the circuit board, this took quite awhile and it was easy to miss some. In fact, the only truly reliable repair would be to remove the solder from each rivlet, snake a bare wire through it, and solder the wire directly to the traces top and bottom. This repair would also take a couple hours and likely be too expensive for a small TV, though if the same chassis were used on a 27 incher, might be worth it.
Here is a case of a piece of equipment being partially destroyed by previous repair attempts. The Pioneer PD5100 is a basic solid CD player but this one had broken parts in the loading mechanism and was in unknown operational condition. If it were taken to a repair shop, the response would probably be something along the lines of: "Well, that certainly looks like a CD player.". It simply wouldn't be worth the time and effort to repair what was obviously broken with the possibility of finding more serious electronic problems after that.
I had nothing better to do (!!) so decided to attempt to restore it to something usable. After repairing the mechanical damage, there was indeed a servo problem which ultimate required the replacement of a motor driver chip - for which I got lucky. The player would read the disc directory but was unable to seek to any track, even #1. One of the chips was getting hot. So, I replaced it and after servo alignment, the play problems were cured. If that hadn't worked, there was probably little more I could have done. Very likely, the servo chip was the original problem and the previous repair attempt created the mechanical mess.
The final example is of a Sony TV that had the infamous tuner/IF box solder problems. This is normally a fairly easy repair, especially for this particular model where the IF box (which was faulty in this case) is readily accessible without taking the whole thing to bits. Once repaired, like the RCA/GE/Proscan TVs with similar solder problems, the result is a solid reliable TV. However, the friend of a friend who had attempted to replace it, apparently used a Weller soldering gun to do the fine soldering, leaving nearly every pad detached or missing. Fortunately, only the pads appeared to have suffered and after 20 minutes and several jumper wires, this one was healthy again.
Repairs for the novice:
It would be way too easy to poison your future outlook on servicing by attempting to repairs multiple times and failing or making things worse.
Equipment that is good to learn on because there will likely be immediate or at least ultimate gratification might include: small appliances, power tools, remote controls, and basic audio equipment like tape decks and low power amplifiers (not big power amps!). And, while electronic troubleshooting of CD players and VCRs is definitely for the advanced course, they often have problems that can be easily remedied by a proper cleaning and/or general maintenance. Electronic problems are tough to diagnose but most are mechanical. Microwave ovens are generally easy to repair but due to the very serious safety issues, I'd suggest holding off on these unless you are experienced in dealing with high voltage high power equipment.
With reasonable care, PC troubleshooting involving basic swapping of components, can also be rewarding. But, don't expect to repair a mainboard with a peculiar failure of IRQ2 (unless you find a lockwasher that ate through to some PCB traces!).
Intermediate level troubleshooting and repair would add TVs since service information in the form of Sams' Photofacts is available for the majority of popular models. Video (not computer) monitors are also straightforward to deal with. And perhaps, audio amplifiers and receivers.
For those just starting out, there are some types of equipment to avoid (beyond those mentioned above). One in particular is modern computer monitors. With their wide scan rate range, microprocessor control, need for decent test equipment, dangerous voltages, and the general difficulty in obtaining service information, even professionals will stay away from many of these - particularly no-name or non-major brand models. Except for obvious problems like bad solder connections, a blown fuse (replace ONCE only, might have been a power surge), or the need for degaussing, they may not be worth the frustration, certainly not as your first project. TVs are not only much simpler than computer monitors, but as noted, complete service information is usually available.
Don't just toss it in the trash. See if a local charity like the Salvation Army or Goodwill accepts broken appliances and electronics. They may have someone on staff who can perform at least simple repairs and then resell the item. Not only will this reduce clutter in the land fill, you may benefit on your taxes (and in the good deeds department). However, it really isn't proper to do this if you have already worked on the item and given up or reduced it to a pile of slag!
If you still doubt the harmful effects of the chemical compounds in tobacco smoke on your health and that of others around you, whatever I say below probably won't matter and you may want to skip it since it may upset you. However, perhaps, you worry more about your fancy, costly, finely tuned electronic entertainment and computer equipment. In that case, read on.
The several hundred chemical compounds found in tobacco smoke have the following effects on electronic equipment. What isn't trapped in your lungs or in the lungs of those around you:
The resulting film WILL eventually cause problems and is very difficult to remove. Damage done due to chemical action may require the replacement of costly parts. Increased maintenance will be needed or the equipment may simply fail before its time and not be worth fixing. Contamination will often find its way into critical places that are not accessible and to media which is irreplaceable.
When someone trys to get me to look at something that has been in a smoker's residence (I know because it will reek of stale tobacco smoke essence), my first inclination is to put it in a sealed bag to go out with the garbage. (I have been known to drop portable TVs directly into the nearest trash can under these circumstances.) If this isn't an option, my next objective is to get it evaluated and repaired or refused as quickly as possible. However, my concentration may not be at its peak for such equipment! It is a good thing that I don't need to do this for a living - I would have to refuse service to a good portion of the world's population :-(.
So, now you have a few more reasons to give up the stupid, disgusting, filthy, obnoxious, inconsiderate of others, costly, dangerous, killer habit!
Sorry, end of editorial. :-)
See the document: Safety Guidelines for High Voltage and/or Line Powered Equipment for general safety information.
See the SAFETY sections of the documents dealing with your equipment for additional safety information for your equipment.
Exceptions include lightning, power surge, dropped, water, or previous repair person damaged equipment. However, multiple electrolytic capacitors in older equipment may be degrading resulting in failures of unrelated circuits. Determine if all the problems you are troubleshooting have just appeared - see below. It is very common to be given a device to repair which has now died totally but prior to this had some behavior which you consider marginal but that was not noticed by the owner.
WARNING: even with an isolation transformer, a live chassis should **not** be considered a safe ground point. This applies mostly to TVs, computer and video monitors, some AC operated strobe lights, and other line connected devices. You shouldn't be touching components with the device powered and plugged in (at least, not until you really know what you are doing!). Once unplugged, sheet metal shields or other ground points should be safe and effective.
Pay particular attention to areas of the circuit board where there are large and/or high power components, connectors, or evidence of discoloration or actual charring due to excessive heat. Your eyeballs, a bright light, and magnifier will be the most useful test equipment for this purpose!
While capacitors will occasionally leak making diagnosis easy, in most cases, there are no obvious signs of failure. (Note: Don't be misled into thinking that the adhesive often used to anchor large capacitors and other components to the circuit board is leakage.) The most useful testing device for electrolytic capacitors is an ESR meter. However, heating suspect caps with a hair dryer may get the equipment going for the purposes of making a diagnosis. See the document: Capacitor Testing, Safe Discharging and Other Related Information.
Common failure items are the large hybrid power regulator ICs used in many VCRs and TVs, diodes and transistors, and remarkably - high value resistors that open up.
Use your senses of sight and smell for the preliminary search for such evidence.
Some discharge sounds are normal for a TV or monitor when powered on or off and occasional sounds of thermal expansion are nothing to worry about. The flyback, yoke, or other (usually) magnetic component may also emit a buzz or while constantly or intermittently without any other symptoms or implication of impending doom. However, repeated loud snaps or a sizzling sounds accompanied by the smell of ozone should be dealt with immediately since they can lead to more serious and expensive consequences.
For any problem but a totally dead VCR, a check should be made for dirty or worn mechanical parts before even thinking about electronic problems or trying to locate a schematic - especially if the unit hasn't been cleaned in a few years.
The reason this works is that the reduced resistance of your moist skin and your body capacitance will change the signal shape and/or introduce some slight signal of its own.
For example, I was able to quickly identify the trigger transistor of in a wireless door bell by using my finger to locate the point that caused the chimes to sound. This quickly confirmed that the problem was in the RF front end or decoder and not the audio circuitry.
Don't get carried away - too much moisture may have unforeseen consequences.
Depending on the condition of your skin, a tingle may be felt even on low voltage circuits under the right conditions. However, this is pretty safe for most battery operated devices, TTL/CMOS logic, audio equipment (not high power amps), CD players, VCRs (not switching power supply), etc.
WARNING: Make sure you do this only with LOW VOLTAGE circuitry. You can easily fry yourself if you attempt to troubleshoot your TV, computer monitor, photoflash, or microwave oven in this manner!
A tech-tips database is a collection of problems and solutions accumulated by the organization providing the information or other sources based on actual repair experiences and case histories. Since the identical failures often occur at some point in a large percentage of a given model or product line, checking out a tech-tips database may quickly identify your problem and solution.
In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts. My only reservation with respect to tech-tips databases in general - this has nothing to do with any one in particular - is that symptoms can sometimes be deceiving and a solution that works in one instance may not apply to your specific problem. Therefore, an understanding of the hows and whys of the equipment along with some good old fashioned testing is highly desirable to minimize the risk of replacing parts that turn out not to be bad.
The other disadvantage - at least from one point of view - is that you do not learn much by just following a procedure developed by others. There is no explanation of how the original diagnosis was determined or what may have caused the failure in the first place. Nor is there likely to be any list of other components that may have been affected by overstress and may fail in the future. Replacing Q701 and C725 may get your equipment going again but this will not help you to repair a different model in the future.
One alternative to tech-tips databases is to search via Google Groups (formerly Deja.com/Dejanews) for postings with keywords matching your model and problem and the newsgroup sci.electronics.repair. See the section: Searching for Information from USENET Newsgroups.
Please see the document: On-Line Tech-Tips Databases for the most up to date compilation of these resources for TVs, VCRs, computer monitors, and other consumer electronic equipment.
Yes, you will void the warranty, but you knew this already.
Hint: The crowbar and 12 pound hammer are *laset* resorts! Really :-).
Manufacturers seem to take great pride in being very mysterious as to how to open their equipment. Not always, but this is too common to just be a coincidence. Opening the equipment non-destructively may be the most difficult and challenging part of many repairs!
A variety of techniques are used to secure the covers on consumer electronic equipment:
These will often be of the Philips variety. (Strictly speaking, many of these are not actual Philips head screws but a slight variation. Nonetheless, a Philips screwdriver of suitable size will work on them.) A precision jeweler's screwdriver set including miniature Philips head drivers is a must for repair of miniature portable devices.
Sometimes, you will find Torx or a variety of security type fasteners. Suitable driver bits are available. Sometimes, you can improvise using regular tools. In the case of security Torx, the center post can usually be broken off with a pair of needlenose pliers allowing a normal Torx driver to be used. In a pinch, a suitable size hex wrench can substitute for a Torx driver. Places like MCM Electronics carry a variety of security bits.
The most annoying (to be polite) situation is when after removing the 18 screws holding the case together (losing 3 of them entirely and mangling the heads on 2 others), removing three subassemblies, and two other circuit boards, you find that the adjustment you wanted was accessible through a hole in the case just by partially peeling back a rubber hand grip! Been there, done that. :(
And on the still lighter side, from an IBM maintenance manual, circa 1925 (displayed in the Chicago Museum of Science & Industry):
"All parts should go together without forcing. You must remember that all the parts you are reassembling were disassembled by you. Therefore, if you can't get them together again, there must be a reason. By all means, do not use a hammer."
When reassembling the equipment make sure to route cables and other wiring such that they will not get pinched or snagged and possibly broken or have their insulation nicked or pierced and that they will not get caught in moving parts. Replace any cable ties that were cut or removed during disassembly and add additional ones of your own if needed. Some electrical tape may sometimes come in handy to provide insulation insurance as well.
For those hard-to-open LCD panels:
(From: Onat Ahmet (firstname.lastname@example.org))
The LCD display housings are usually secured by plastic catches built into the case. They still may have a couple of screws that are positioned in the most innovative places! Obvious places are sides of the display, and under stickers (rub your finger over a sticker and see if you can feel the hole for a screw). Also, try to look around the hinge connecting the LCD to the main housing. Look with the LCD closed, and also open; rotating open the housing might hide some screws from view. Expect it to be awkward! BTW, do not forget small hatches, that do not look like one!
After that, it is patience, and knowing the right place to twist the case to pop it open. Try not to use screwdrivers; they leave unsightly marks along the seam.
Also, if it is your own unit, and you break a few of the catches along the way, do not worry; you can put the housing back together with a few spots of adhesive.
These are in no particular order.
(Portions from various people including Alan Liefting (email@example.com), Heath Young (firstname.lastname@example.org), Craig Osborn (email@example.com), Phil Allison (firstname.lastname@example.org), Franc Zabkar (email@example.com), and Sam.)
Some basic hand tools.
It may be possible to remove such screws even if nothing in your driver assortment quite fits (short of buying the proper tool, that is - what a concept!). There is also the situation (very common) where someone (we won't say who) has pre-mangled the screw head! Here are a few approaches to try when you are stuck at 2:00 AM on a Sunday morning with an uncooperative screw:
Note: some of these screws have had some material like Lock-Tight(tm) (which looks like colored nail polish) applied to the top to prevent the screw from loosening on its own. This also prevents the blade of a screwdriver from properly seating, so removal is essential before attempting removal.
There are many other possibilities.
To avoid this problem in the future, realize that plastic is very soft and it is essential to gently start the screw into the hole to get a feel for it properly mating with the existing threads. The use of an undersized screwdriver to get the screw started may be helpful in that it won't accidentally apply too much torque and strip the threads. Something that is less obvious is that screws for plastic are often made with a wide thread and a narrow thread wound that alternate, sort of like a deformed hunk of DNA. :) With these, there is only one proper way for them to mate with an existing hole and forcing them is asking for stripped threads and a fine strand of plastic being pulled out along with the loose screw.
As well as Phillips, there are Pozidriv and JIS:
Pozidriv screws can be recognized by the 'starburst' - the little lines on the head between the main slots. These are very common (certainly in Europe) in all sorts of equipment.
It's not uncommon for all 3 to be used in the same equipment, especially if subassemblies were made by different companies.
(From: Robert McPherson (firstname.lastname@example.org).)
There is a type of screwdriver called a "Reed & Prince" which fits these screws which are similar in appearance to Phillips screws. Cooper tools makes them.
A size of 3 x 6 feet should be adequate, longer is better if you have the space. Workbench height is typically 36 inches. Make sure the legs are sturdy and rigid - some equipment can be quite heavy. Get yourself a comfortable stool to sit on for those marathon troubleshooting sessions.
The surface can be laminate, particle board, plywood, butcher block, or some other insulator. It shouldn't have a dramatic pattern though since small parts will be hard to find. Wood products should have multiple coats of varnish or polyurethane. Using a cheap material that can be replaced will enable the surface to be rejuvenated after it gets pitted and burnt - as it invariably will after awhile. An antistatic surface is desirable but probably expensive to put on the entire workbench so just get an antistatic matt for use when needed. (An antistatic surface isn't quite a perfect insulator but has just enough conductivity to minimize the buildup of static electricity, essential for any work with devices like CMOS ICs and laser diodes that can be destroyed by even a small static discharge.)
Install a shelf or shelves along the back that are about half the depth of the workbench surface to hold smaller pieces of test equipment, power supplies, parts cabinets, and other odds and ends. Add a shelf or shelves underneath for storage.
Install AC outlets along the rear edge, vertically so debris can't fall into the holes. How many? The more the merrier - they will all get filled no matter how many are there! At a minimum, one every 6 inches or a duplex every foot, double this won't hurt. Power the workbench from two branch circuits fed from opposite sides of the 115-0-115 VAC (in the U.S.A.) Consider including at least one 230 VAC outlet (in the U.S.A.). Providing some outlets that are switched with power indicator lamps and protected by fuses or circuit breakers. Most outlets, particularly those used to plug in equipment being worked on, should be GFCI (Ground Fault Circuit Interrupter) protected for safety. But a few - clearly marked "NOT GFCI PROTECTED" - should be available for equipment that will not function reliably on a GFCI with the understanding that these lack such protection. Most test equipment and power supplies with properly wired grounded power cords do not need to be GFCI protected but won't complain if they are. However, some equipment may nuisance trip (immediately or at random) GFCIs even if functioning properly.
The total cost can be well under $100 for all of this even if the materials and parts are purchased new. With some reasonable scrounging abilities, it can be a lot less.
A fancy expensive multimeter is not needed, at least not while you are just starting out (and likely to make some occasional mistakes like attempting to measure line voltage on the ohms scale.) However, if someone offers to give you a nice Fluke DMM, don't turn it down :-).
Scales for transistor, capacitor, frequency counter, etc. are not really essential. A diode test function on a DMM is needed, however, to properly bias semiconductor junctions. Even this is not useful for in-circuit tests or for some power transistors or transistors with built in damper diodes and/or base resistors.
Make sure you have a good well insulated set of test probes. This is for your own safety as you may be measuring relatively high voltages. Periodically inspect for damage and repair or replace as needed. If the ones that came with your multimeter are substandard - flimsy connectors or very thin insulation, replace them as well.
A high impedance high voltage probe is sometimes useful for TVs and monitors. You can build one of these which will suffice for most consumer electronics work.
I would recommend a good used Tektronix (Tek) or Hewlett Packard (HP) scope over a new scope of almost any other brand. You will usually get more scope for your money and these things last almost forever. Until recently, my 'good' scope was the militarized version (AN/USM-281A) of the HP180 lab scope. It has a dual channel 50 MHz vertical plugin and a delayed sweep horizontal plugin. I have seen these going for under $300 from surplus outfits. For a little more money, you can get a Tek 465 or 465B (slightly newer but mostly similar specifications) 100 Mhz scope ($200 to 600) which is what I use now. The HP-180 is still fine but I couldn't pass up a really good deal. :) The Tek 465/B or other similar model will suffice for all but the most demanding (read: RF or high speed digital) repairs. (See the additional comments below on the Tek 465 as well.) From my experience with this scope many years ago and now as well, I really do agree with some who say that this is the best scope Tektronix ever designed.
Auctions like eBay can sometimes be a source of good used Tek and other scopes at reasonable prices though sometimes the bid price goes way beyond what is reasonable. :) A search for "oscilloscope" will typically turn up several hundred hits. However, to have any confidence in the operational condition of a scope, the seller must be reputable and know something about testing them. A warranty may be of limited value since a major part of the cost of a used scope is likely to be the shipping and you'd end up having to pay that both ways. Check out Phil's Tek Scope Prices on eBay List as well as catalog pages of surplus test equipment dealers. A Web search (e.g., Google) will usually turn up enough sites for any specific model to provide both specifications and typical prices from surplus equipment dealers (which are usually high!).
My instant checklist for a used scope:
You don't absolutely need an oscilloscope when you are just starting out in electronics but it would help a great deal. It need not be a fancy one at first especially if you are not sure if electronics is for you. However, being able to see what is going on can make all the difference in your early understanding of much of what is being discussed in the textbooks and the newsgroups. You can probably find something used that will get you through a couple of years for less than $100. An oldie but goodie is much better than nothing at all even if it isn't dual channel or high bandwidth!
And a note about digital versus analog scopes: Analog scopes are what we used to think of as an oscilloscope: The CRT is the place where the waveform is generated. Digital scopes use a fast A/D converter to capture data in memory in the form of 1s and 0s and then display this on a raster-scan CRT (like a computer monitor screen). Digital scopes are automatically storage scopes and are great for analyzing waveforms. However, most older digital scopes are really poor at real time display and in addition, appear to have been designed by computer programmers, not test equipment engineers. Ever try to play a menu-driven piano? :) For general electronics and troubleshooting, I'd rather have a 20 year old Tek analog scope than a 5 year old digital scope costing 25 times as much. The inherent real-time presentation of an analog scope can be invaluable when attempting to observe the subtle characteristics of a waveform. Those who go through school never having touched a true analog scope have missed out on a great experience.
A great deal of information can be gathered more quickly by examining the picture on a TV or monitor than can be learned from the video waveform on displayed on a scope.
For audio, a simple transistor or 555 timer based battery powered oscillator can be built into a hand held probe. Similar (but generally more specialized) devices can be constructed for RF or video testing.
If you are buying a used 465, look for the 465B. It is a better unit, and is the same price most of the time. Take care that this scope is about 20 years old, and there is no support from Tek on it. The replacement parts are not available if something blows. I used to have a few of them. One needed a CRT, and the other I sold while it was still working. For consumer electronics, you will get by with a 100 MHz unit, but it is preferable to have over 200 MHz bandwidth if you want to do front end service on consumer FM radio receivers. Read up on Nyquist and you will see the answer.
If you also call Tektronix technical services, tell them that you are looking for a used Tek scope to be used for hobby purposes. They will be very helpful in giving you any information you require. They will even recommend models and what to look for. If you talk to their sales people, they will sometimes even give you their authorized dealers who handle used Tek equipment so that you can shop around.
If you go a bit more for your used scope you can get a 200 or 300 MHz unit that is a newer version of an analog scope. It will have improvements over the 465 series. Look at the 2000 analog series scopes. These have a lot of enhancements like on the screen display. This will be very handy for precise work. When buying any type of scope, I would stress that the Tektronix is the best. If you find a good working used one, you will have a very high quality product, and it should give you years of service. Most of the analog scope that they made include the TV sync options.
Even if you buy a used one, and the parts are not available, it pays then to buy a second used one and you will have spare parts. These scopes used to cost in the many thousands of dollars when new, and you are probably paying between eight hundred to fifteen hundred for a used one (somewhat cheaper now, even from surplus companies. --- Sam). These scopes will be far superior to even the newer ones from the consumer level scopes. In 1978 I believe my company paid over $8,000 for the 465B scope new. A new Chevy fully loaded was less!
The most likely causes are shorted tantalum "dipped" capacitors dragging down one or more power supply rails. Apparently, Tek used a batch of unreliable caps on the some of the 400 Series scopes and while aluminum electrolytics usually just dry out with decreased capacitance and increased ESR, these dipped tantalums go short circuit. Fortunately, the design of the switching power supplies in these scopes is such that the controller shuts down from a serious overload or short rather than letting its smoke out. If the overload is on only one voltage rail and not severe (e.g., through a resistor), only that voltage may be low or absent resulting in loss of functionality but not a totally dead scope.
So, the first step is (WITH POWER OFF) to check the resistance of each voltage test point to ground with a multimeter. While the expected resistances may not be known except from a service manual (if that), anything very low (e.g., 10 ohms) is suspect. Here are typical values measured on a Tek 485 using a Fluke 87 DMM with the black lead on ground: +50 V, 2.1K ohms; +15 V, 89 ohms; +5 V, 70 ohms; -5 V, 222 ohms; -15 V, 152 ohms. The resistance for +5 V changes significantly depending on front panel settings and which incandescent indicator lamps should be lit and may go below 35 ohms. On this scope, the -15 V rail originally measured about 10 ohms due to a bad cap. Where one of these is found, attempt to determine the location of the short to a specific circuit board. Then, trace the wiring on that board to locate the possible bad caps. A good DMM or milliohmmeter can help to track down the cap since PCB foil resistance is high enough to be measured and the resistance to ground will be lowest at the location at the bad cap. At this point, unsoldering one lead of each cap and checking its resistance is the safest approach. With care, this can be done from the component side of the board which is fortunate since removing some of these large PCBs can be a royal pain. Heat the lead with a soldering iron and pull it free. Then, use a vacuum desoldering tool ("SoldaPullet") to clear the hole. Check the resistance of the cap and/or across the supply rail to determine if you found the correct one. The bad cap mentioned above was found in about 5 minutes in this manner. There are typically only a few of these caps on each board but it's possible for the bad one to be on a board that isn't easily accessible.
Where this approach doesn't work or for the lazy but daring among us, the alternative is to apply voltage from an external adjustable current limited supply to the bad power rail. If the bad part isn't a perfect short circuit, it will dissipate heat and let its smoke out or explode. Wear safety glasses! If this doesn't happen, it may actually be possible to power up the scope with the external voltage applied to determine functionality. In either case, I won't be responsible for any destroyed equipment should this be done.
However, there may be no need for such extravagance. If you have an oscilloscope and camcorder or video camera/VCR, you probably have all that is needed.
For a TV or monitor, point the camera at the CRT and the scope screen so that they are both in the picture and record on a 6 hour tape. Then, when your event takes place, you have a permanent record!
That old video camera will be perfectly adequate. It doesn't need a 100X digitally stabilized enhanced reprocessed zoom or 1/10,000th second shutter. It doesn't even need to be color!
Sure, this won't capture the 1 ns glitch. But, for the occasional flash in the picture, it is more than adequate to eliminate a video signal line as the source of the problem.
Extensions to more convoluted problems are left as an exercise for the student!
Since Earth Ground and the Neutral of the power line are connected together at your service panel (fuse or circuit breaker box), grounds like cold water pipes, test equipment chassis, and even a damp concrete floor make suitable returns for the line voltage (Hot or live wire). Since this is just as true with the conductor being being a wire or your body, such a situation is very dangerous.
An isolation transformer as its name implies provides a barrier such that accidental contact with an earth ground results in negligible current flow (only due to the parasitic capacitance and inductance of the transformer) - a slight tingle at worst. This also protects your test equipment as well as the device you are troubleshooting since a similar accidental contact can result in a short circuit, sparks, smoke, and many destroyed parts.
The schematic for a typical isolation transformer is shown below:
_ 1:1 H o-----/ ----- _------+ +-----------o 115 V Power Fuse )||( Switch )|| +-----------o 105 V )||( )||( Primary )||( Secondary Tied together at )||( service panel )||( | )||( | )||( +-> N o----------+---------+ | +---+--------o Return | | 4.7 M* | | | +---/\/\----|------+ | | +-> G o----------------------+--------------o GroundNote: Ground is included on the secondary side. This is actually needed for safety with certain types of equipment like microwave ovens where the HV return is to the chassis. Most other consumer electronic equipment and appliances will only have a 2 wire cord and thus not use the Ground. However, a potential safety hazard can arise if some other piece of equipment develops a ground fault resulting in a live, non-isolated part being user-accessible so this must be taken into consideration in deciding whether to ground the secondary side.
The resistor (*) is desirable to permit any static charge to leak off to ground. Since it is quite large - 2 M ohms - no perceptible current will flow between the secondary and primary sides but this value is low enough to dissipate any static charge. CAUTION: The resistor must be a high voltage rated type (as in 4,200 V isolation, large size light blue color to assure that arc over will not result due to voltage differences that may be present when the isolation transformer is being used in its normal manner.
Although the power line Neutral and Ground wires are tied together at the main service panel (fuse or circuit breaker box), the transformer prevents any significant current flow between any of its outputs and earth ground should a fault occur.
Even if you were standing with bare feet in a puddle of salt water on a concrete floor (noting that this is definitely NOT recommended) and were to touch something connected to the secondary of the isolation transformer or its return, or equipment circuitry attached to these, there is no direct return path for current to flow through you.
However, this shouldn't encourage a false sense of security. If you were to touch two points at different potentials on the secondary side, you could still be fried! And some equipment like microwave ovens use their chassis, and thus ground, as the high voltage return so an isolation transformer is of limited value for these whether it passes ground through or not.
Isolation transformers can be purchased or constructed from a pair of similar power transformers connected back-to-back. I built mine from a couple of old tube-type TV power transformers mounted on a board with an outlet box including a fuse. Their high voltage secondary windings were connected together. The unused low voltage secondary windings can be put in series with the primary or output windings to adjust voltage. See the section: Typical Homemade Isolation Transformer.
For super critical applications like in hospitals where every microamp of leakage counts, special isolation transformers are available (no doubt at equally super cost) which have shielding between the primary and secondary to minimize the inter-winding capacitance and inductance as well. This should not really be necessary for general servicing.
Note: Not all definitions of the term 'isolation transformer' are created equal! For some purposes, this may mean just preventing line born electrical noise from passing to the equipment. So, if you acquire something called an 'isolation transformer' on its nameplate, confirm that the primary and secondary are indeed not tied together by a low resistance. If they are, it can probably be modified for service needs by disconnecting a jumper but it may not have the insulation ratings desirable for high voltage isolation.
(From: Filip "I'll buy a vowel" Gieszczykiewicz (email@example.com).)
Ever wonder how those guys repair HV transformers running 200 kV without shutting off the power lines feeding the city? They use *very well isolated* cherry pickers! The guy on that platform is working on ONE wire which - since he's not connected to the ground - is at ZERO potential! That wire has no reference at all so no current flows. And he prays each morning that it stays that way or he goes off with a flash! [ugh!].
You're doing something like that on a much safer level. :)
+-------------------------o 109 V | | +-------------------o 121 V | | | +---------------+ | | | | || +--o NC | | +---+ || | ||( | | )|| | ||( | | 6.3 V )|| | || +--o NC | +-------+ || | _ ||( | )|| | H o--/ ----- _---+ ||( | 6.3 V )|| +--+-------o 115 V Power Fuse )|| +--o NC +---------+ ||( Switch )|| +-------------------+ ||( 115 V )||( )||( 115 V )||( )||( )||( 350 V 350 V )||( N o---------+----+ ||( )|| +----+-------o Return | || +--o NC NC o--+ || | | ||( )|| | | ||( )|| | | ||( 350 V 350 V )|| | | ||( )|| | | | +-------------------+ | | | Pri1 | Sec1 Sec2 | Pri2 | G o----------------+-------------------------+-------------o Ground | Transformer 1 2M* Transformer 2 | +------------------/\/\-----------------+Note that there should be a fuse in the primary to protect against faults in the transformer as well as the load. A slow blow type should be used in the primary circuit. The inrush current of the transformer will depend on the part of the cycle when the switch is closed (worst is actually near the zero crossing) as well as the secondary load. To protect the load, a fast blow type in the secondary is recommended. However, the inrush current of the degauss coils in TV sets and monitors, for example, will often pop a normal or fast blow fuse when no actual problems exist. (It is probably a good idea to disconnect the degauss coils while testing unless they are suspected of being the source of the problem.)
The 2 M resistor (*) is to bleed away any static charge as described above.
The power/VA ratings of the transformers you use need to be greater than your expected load. And, since some equipment like TVs and computer monitors draw a lot of current at power-on (from the degauss circuit), the isolation transformer will limit the peak current and may cause problems during startup (though overall, the limited current may prevent some types of disasters!). In any case, don't expect a pair of 6.3 VAC, 1 A transformers wired back-to-back to be useful for testing much of anything!
Also see the section: Isolation Transformers from Dead Microwave Ovens.
(From: David Moisan (firstname.lastname@example.org).)
It's not as hard as you think to find inexpensive isolation transformers. At the next hamfest, look for someone selling dead UPS's (Uninterruptible Power Sources) or other power conditioning equipment. Isolation transformers are often sold for use in the computer industry; that's how I got mine. 250 VA for $20, and I could have gotten 1000 VA for $50 if I wanted. Definitely increases my safety *and* confidence level!
However, note that microwave oven transformers are usually designed with as little copper as possible in the primary winding and do go into core saturation at normal line voltage with no load. For example, measurements using a clamp-on AC ammeter of a transformer from a mid-size microwave oven shows:
Input VAC Input Amps ------------------------ 80 .3 90 .6 100 1.1 110 2.0 115 3.0 120 >4.0At 115 VAC input, that's about 350 VA - probably close to 350 W with nothing connected to its secondaries! It also had a very noticeable hum above about 100 VAC.
Thus, this sort of approach isn't recommended unless you really need the high capacity - testing of other microwave ovens or ion laser power supplies, for example!
A pair of these trnasformers can be connected in a similar manner to the tube-type TV power transformers described in the section: Typical Homemade Isolation Transformer, there are a few more things to keep in mind:
Keep in mind that I am not talking about using something that has been rusting away in a damp basement for 20 years. The power transformers from tube-type TVs or audio amplifiers must have been designed with isolation requirements in mind to obtain regulatory approval in the first place since they are used in equipment where the user may come in contact with metal parts.
Also, the use of an isolation transformer is no excuse to ignore the other aspects of safe troubleshooting.
It is easy to test for AC and DC leakage - and this should be done - to be sure that your transformers are in good condition. With two transformers, the probability of a failure is even smaller - 1/(P*P). Personally, I would trust the homemade transformer over a cheap import any day!
The internal wiring of a typical Variac is shown below:
_ 1 H o---- _-----/ ------>o--+ Tap 1: 0 to 115 VAC Fuse 1 Power 2 )|| (Input) Switch o--+ || Tap 2: 0 to 140 VAC )|| )|| _ Tied together at )<------- _--------o Adjustable output service panel Power )|| Fuse 2 | 220 LED )|| (Output) | +--/\/\--|>|--|>|--+ || | | )|| +-> N o----+------------------+-|-----------------o Return | | +-> G o-------------------------+-----------------o GroundWARNING: Direct connection between input and output - no isolation since the power line Neutral and Ground are tied together at the main service panel (fuse or circuit breaker box)!
CAUTION: Keep any large transformer of this type well away from your monitor or TV. The magnetic field it produces may cause the picture to wiggle or the colors to become messed up - and you to think there is an additional problem!
Note: the 'Power LED' circuit is soldered directly to a winding location determined to produce about 6 VAC.
Wiring is straightforward if you have acquired a bare unit (the following assumes a 115 VAC line, the extension to 230 VAC should be obvious):
Note that while isolation may be provided, it is NOT inherent in this technology. Some types may use autotransformers and thus have no isolation.
(From: Dave Martindale (email@example.com).)
The simplest version has fairly ordinary-looking primary and secondary windings wound on the centre leg of a shell-type transformer core. Unlike a normal transformer, where the primary is wound over the secondary (or vise versa), the primary and secondary windings are physically separated. Magnetic shunts (chunks of transformer steel) are inserted between the centre and outside legs of the core at a point between the primary and secondary winding. These magnetic shunts provide a flux path around the primary that bypasses the secondary winding, producing lots of leakage inductance. This is what limits the current when the secondary is shorted.
Meanwhile, the secondary winding is in parallel with a capacitor, chosen to make the secondary resonant at 60 Hz. The resonance drives the portion of the core inside the secondary winding into saturation, which limits the amplitude of the secondary voltage. Changes in primary voltage have almost no effect on secondary voltage over the regulating range.
Now, the above is actually a simplification. In real CV transformers, the secondary actually has enough turns to step up the voltage by a factor of several, so the capacitor is operating at several times line voltage. This allows the capacitor to be lower capacitance for resonance, which is physically smaller and cheaper than what you'd need at 115 V. The actual output voltage is obtained from a tap on the secondary where the voltage is 115 V or so.
Also, the transformer I've described so far outputs a pretty square waveform. That's great for the input stage of a DC power supply, but not for some AC loads. The commercial CV transformers I see use a "harmonic neutralized" design that gives an output closer to a sine wave. Instead of one secondary winding, there are two, with another pair of magnetic shunts between the two secondaries. The capacitor is connected across the two secondary windings in series. The output voltage is taken from just the "middle" secondary winding. In the Sola transformer, there's also an air gap in the centre leg of the core, at the end where the 3rd winding is. I don't understand how the extra winding and shunt cancel some of the 3rd harmonic output, but they do.
Actually using a series load - a light bulb is just a readily available cheap load - is better than a Variac (well both might be better still) since it will limit current to (hopefully) non-destructive levels.
What you want to do is limit current to the critical parts - usually the horizontal output transistor (HOT). Most of the time you will get away with putting it in series with the AC line. However, sometimes, putting a light bulb directly in the B+ circuit will be needed to provide adequate protection. In that location, it will limit the current to the HOT from the main filter capacitors of line connected power supplies. This may also be required with some switchmode power supplies as they can still supply bursts of full (or excessive) current even if there is a light bulb in series with the AC line.
Actually, an actual power resistor is probably better as its resistance is constant as opposed to a light bulb which will vary by 1:10 from cold to hot. The light bulb, however, provides a nice visual indication of the current drawn by the circuit under test. For example:
The following are suggested starting wattages:
Depending on the power rating of the equipment, these wattages may need to be increased. However, start low. If the bulb lights at full brightness, you know there is still a major fault. If it flickers or the TV (or other device) does not quite come fully up, then it should be safe to go to a larger bulb. Resist the temptation to immediately remove the series light bulb totally from the circuit at this point - I have been screwed by doing this. Try a larger one first. The behavior should improve. If it does not, there is still a fault present.
Note that some TVs and monitors simply will not power up at all with any kind of series load - at least not with one small enough (in terms of wattage) to provide any real protection. The microcontroller apparently senses the drop in voltage and shuts the unit down or continuously cycles power. Fortunately, these seem to be the exceptions.
The behavior of a phase control device like a light dimmer depends critically on what sort of load it sees. If the dimmer sees mostly a resistive load, it will work reasonably well and survive. However, most electronic equipment doesn't fall into this category. If the dimmer is attempting to drive a piece of equipment with a lot of capacitance or inductance, at the very least it will behave strangely with the control range squashed to one end or the other, or the output voltage will change suddenly rather than smoothly. But more likely, it will self destruct and/or damage the equipment due to the strange waveform, which may result in a peak output voltage that approaches full line voltage even at relatively low settings. There's also usually a minimum load below which it won't do anything predictable. In short, get a proper Variac. You know my motto: "You can never have too many Variacs!". :) Surplus Variacs are readily available including on eBay.
Without an isolation transformer, connecting the scope ground clip to the return will result in a short through the ground lead between the equipment and earth ground. There will be smoke and possibly blown components as well. Disconnecting the scope from ground allows its case to float which will prevent the melt-down but is EXTREMELY DANGEROUS since the entire scope cabinet is effectively connected to the power line. You (or someone else not familiar with your foolishness) may casually touch or lean against the scope cabinet and be thrown across the room if it is a lucky day or worse. Don't do it! Invest in an isolation transformer. It is very cost effective insurance.
Special cut-down miniature test CDs can be made to view the lens motion while focusing and to permit access to adjustments blocked by normal CDs in many portable players. See the document: Notes on the Troubleshooting and Repair of CD Players and CDROM Drives for details.
An IR detector will be needed to confirm laserdiode operation.
An audio amplifier with speakers or headphones will be needed for the audio tests, or headphones if the unit has a headphone jack. A TV or video monitor will be needed for Laserdisc video tests.
A typical schematic is shown below:
H o-------/ ---+-------+ Power | | H N Switch / +--| |--+ Current limiting load \ | 47K / o G | \ | | +---------+ +++ | H N NE2H |o| +--| |--+ Device under test Power |o| | Light +++ o G | | | | N o------------+-----------------+ | G o-------------------------+
Note: Ground connections normally not used for equipment likely to be tested using this device.
See the repair guides for specific equipment for more details on the use of the series light bulb.
Safety note: always double check that capacitors are fully discharged with a voltmeter before touching any high voltage terminals!
See the document: Capacitor Testing, Safe Discharging and Other Related Information for additional information.
See the document: Notes on the Troubleshooting and Repair of Video Cassette Recorders for additional construction details.
See the document: TV and Monitor CRT (Picture Tube) Information for additional information on CRT magnetization and degaussing techniques.
See the documents: "Notes on Troubleshooting and Repair of Audio Equipment and other Miscellaneous Stuff" and "Notes on Troubleshooting and Repair of Video Cassette Recorder (VCR)" for additional information on tape head demagnetizing.
Caution: do not use a demagnetizer on video heads unless specifically designed for them. Some are strong enough to damage the fragile ferrite cores. Video heads generally do not require demagnetizing anyhow.
See the document: Notes on the Troubleshooting and Repair of Hand Held Remote Controls for construction details.
See the document: Testing of Flyback (LOPT) Transformers for additional information.
If you have a current probe for your scope, this can be used to monitor the various current waveforms. I have used my Tektronix current probe to view the yoke current on TVs. The rendition of the horizontal deflection current waveform is quite good. However, the vertical suffers from severe distortion due to the low frequency cutoff of this probe.
You can build a not-very-fantastic (but quite usable) current probe using a split ferrite core of the type used on keyboard and monitor cables (preferably one that snaps together). The following will work:
You can experiment with the number of turns and load resistor value for best results.
To use your fabulous device, insert one and only one of the current carrying wires inside the ferrite core and clamp the two halves together.
For a typical TV horizontal deflection yoke, this results in about a .3 V p-p signal. The shape was similar to that from my (originally) expensive Tektronix current probe. Enjoy the show! Due to its uncompensated design, this simple probe will not work well for low frequency signals.
There is info on useful devices for your scope that you can construct in about 10 minutes. These won't replace a fancy Tek 576 but may be all you need (or at least can justify on a finite budget).
WARNING: Use an isolation transformer with this device since it is line connected without isolation. The maximum sustained (short circuit) current is only 4 or 5 mA but this is still enough to be dangerous so respect it even with the isolation transformer!
C1 D2 AC H o----||--------------+----|>|----+-----+----o +DC .2uF | 1N4007 | | 250V D1 | | / +---|>|---+ C2 _|_ \ R2 | 1N4007 .5uF --- / 5M | 400V | \ R1 | | | AC N o---/\/\---+---------------------+-----+----o -DC 3.3K
Exactly why this is no longer done except to save money isn't quite clear. Chassis of modern equipment like TVs, computer monitors, microwave ovens (especially microwave ovens) are very dangerous. Perhaps the manufacturers figure that at least for the first two, not using vacuum tubes, most of their voltages are lower. More likely, since they provide the warning "no user serviceable parts inside", they figure that they can't be sued and it is isn't worth spending the 10 cents for the extra plug. :)
Where your equipment actually has this sort of interlock, it is usually possible to pop off a retaining clip and use the original cord for this purpose. Just make sure you understand the safety issues. Modern devices may not have several hundred volts sprinkled all over the chassis like those using vacuum tubes, but there may be non-isolated line voltage, 25 kV or more for the CRT, or 5,000 V at AMPs in a microwave oven. You can be just as dead from these!
(Portions from: Raydon Berry (firstname.lastname@example.org).)
Take a small piece of stiff plastic (e.g., as used in blister packs) and attach strips of self adhesive copper or aluminum foil to both sides. Shape one end of the strip into a sort of finger, narrow enough to slip between the AA or AAA batteries or batteries and the contact when they are installed in the holder. If the foil is copper, wires can be soldered to each side at the other end. If aluminum, cut away a portion of the foil in opposite locations on both sides so clip leads from a multimeter can be attached without shorting.
This device is used (frequently by me) for checking the current consumption of all battery powered equipment - it's very simple and very cheap.
For example, with remote controls, insert between batteries and put the multimeter on a range of about 25 mA and when you press each button, the code being sent will show up as a wagging needle on a VOM or an average current for a DMM. If the ceramic filter or the IR diodes have failed, the current remains very low, but if OK, you should see pulses of 5 to 10 mA.
For other devices, select an appropriate range. It might not be a bad idea to check new/working equipment as well to obtain a "signature" of health which is recorded on a slip of paper glued inside the battery compartment. Then, if the device should fail, a comparison can easily be made.
Red: +5, Yellow: +12, Black: Gnd (Probably case as well).
White: -5, Blue: -12, Orange: Power_good (output).
(Some newer supplies may have a +3.3 output as well which may be green).
I use an old dual beam auto headlight. It adds a touch of class as well to an otherwise totally boring setup :-). You can also use auto tail light bulbs or suitable power resistors or old disk drives you don't really care about (you know, those boat anchors).
J8: Pin 1 = Power_Good J9: Pin 1 = Gnd Pin 2 = +5 Pin 2 = Gnd Pin 3 = +12 Pin 3 = -5 Pin 4 = -12 Pin 4 = +5 Pin 5 = Gnd Pin 5 = +5 Pin 6 = Gnd Pin 6 = +5Note: for an XT only, J8-Pin 1 is Gnd, J8-Pin 2 is no connect.
However, the purpose of solder is not to physically anchor connections - they must be mechanically secure first to assure reliability. When properly done, solder actually combines with the clean metal surface of the wires, pins, and terminals assuring a low resistance connection.
While there are several conditions must be satisfied to achiev good reliable solder connections, with a little practice, soldering will become essentially automatic and you will know immediately when the results are satisfactory.
There have been entire handbooks written on proper soldering technique. Organizations like NASA take this seriously - after all, a service call to the one of Jupiter's moons would be quite costly!
Aditional information on soldering techniques and equipment can be found at:
I consider fine gauge rosin core solder (.030 or less) to be best for most applications (e.g., Ersin Multicore).
However, there are times where soldering is more convenient. Use of the proper technique is critical to reliability and safety. A good solder connection is not just a bunch of wires and terminals with solder dribbled over them. When done correctly, the solder actually bonds to the surface of the metal (usually copper) parts.
Effective soldering is by no means difficult but some practice may be needed to perfect your technique.
The following guidelines will assure reliable solder joints:
For stubborn joints or those connecting to the power planes (surface or multilayer boards), you may need to add some fresh solder and/or flux and then try again. Generally, if you only get part of the solder off the first time, repeated attempts will fail unless you add some fresh solder.
Other approaches that may be used in place of or in addition to this: Solder Wick which is a copper braid that absorbs solder via capillary action; rubber bulb type solder pumps, and motor driven vacuum solder rework stations (pricey).
(Portions from: Pat Brunner (Brunner@ieee.org).)
I have used a SoldaPullet for 30 years but found an inexpensive improvement. Add a 1 inch length of silicone tubing (or something else that won't be damaged by the heat, 1/8" ID x 1/4"OD) over the SoldaPullet tip leaving 3/16" to 1/4" extending past the tip. This absorbs the downward force when the SoldaPullet is fired reducing damage to the PCB, provides a better seal around the component lead so it's often possible to clear a hole in one operation that might otherwise require several, and it prevents the plastic tip of the SoldaPullet from being damaged.
(From: Nicholas Bodley (email@example.com).)
A few points to keep in mind...
Try to get cutters that will let you snip individual leads on the IC. Get tool catalogs! I like Contact East, in the USA; not sure about Canada. Jensen, in Arizona, I think, tends to be costly.
If you snip all the leads on one side, you can bend the IC back and forth to break the other side free, but be sure to do the bending next to the plastic (it's harder to do there).
When you cut the IC leads, do your best to leave most of each lead sticking up above the surface of the board.
Set your iron to about 770 deg. F (400 deg. C). (This assumes a modern soldering station with a temperature control, and a relatively-slender tip.) Be sure that the tip is clean and shiny and properly tinned. Any oxidation is just no good. (DON'T file modern plated tips! You'll remove the plating!). Be fanatical about ensuring that the tip always idles with a decent coating of solder.
Hotter temps run a real risk of spoiling the adhesive bond that holds the copper foil to the board. DO NOT use a higher temp to make up for an improperly-tinned tip!! (You might need a higher temp for holes in the middle of ground planes, however. These will sink the heat away effectively; but do those separately.)
You must get each pad hot enough to be well above the melting point, so that the cold air won't make the solder resolidify when you slurp it up.
To transfer enough heat, you must have a fillet of solder between the tip and the pad. If necessary, add a bit of solder to ensure this!
After hitting these points so hard, I'll relax and say that you'll really do better if you remove each lead stub individually with assembly tweezers (AA style are good) or thin needle-nose pliers.
Once they're all out, then you need to be concerned about heating the pads enough. Now you can desolder. The other messages in this post have good advice on that.
You need to maintain your desoldering tool, too. It might not have good vacuum if ignored.
It's tricky to hold the iron on the pad while getting the nozzle close enough, but a decent desoldering tool will work if tilted somewhat to let the tip contact the pad.
If a hole doesn't open, but some solder has been slurped up, you could try good solder wick (Solder-Wick (Soder-Wik?) brand is good); it can sometimes pull up solder from underneath by capillary action. (I didn't believe this until it happened!) Poor solder wick isn't fluxed sufficiently, or might be subtly corroded. It should soak up solder like a sponge.
It might be quicker to refill the hole with a bit of solder and repeat; there could be a good blob of it on the other side, which you might, or might not, be able to get to.
(If you can get to both sides, and have five hands, you could apply heat to one side, let the tip dwell for a few seconds to melt all the solder, and slurp from the other side.)
If things become messy, apply liquid flux (seems not to be too easy to find in small quantities; I use a flux pen, which seems not overpriced). Reheat the pad, and the flux should do a great job of tidying things up. It tends to let capillary action make the holes open wider, when most of the solder has been picked up.
I think it's well worth the effort to cut the leads free from the IC body and remove them one at a time, then go over the pads a second time to remove the solder.
I have very recently removed a 16-pin DIP twice from a location without damaging the pads at all by these principles.
It's much harder, or impossible, to do good work with poor tools. Do try to get good tools, and learn to take care of them.
One approach that works in some cases is to use the mating socket to stabilize the pins so they remain in position as you solder. The plastic will still melt - not as much if you use an adequately sized iron since the socket will act as a heat sink - but will not move.
An important consideration is using the proper soldering iron. In some cases, a larger iron is better - you get in and out more quickly without heating up everything in the neighborhood.
But if there is actual damage to the board material itself, then the carbon that is present and can't be removed will result in a conductive path which may result in circuit failure or erratic behavior. It would be best to replace the entire PCB if possible. But a more realistic alternative is to cut out the bad section and build the missing circuitry on a separate prototyping board.
Note that sometimes plain water will work better for sugar based coatings. Tape head cleaner can be used for head cleaning as well.
Thermal resistance (°C/W) for silicone heatsink compound:
Insulator Without With ------------------------------------ None 0.20 0.10 Anodized Aluminum 0.40 0.35 Mica 0.80 0.40 Teflon 1.45 0.80
Note that using no insulator is always better than one with heatsink compound for these materials (no data on BeO which may be the exception).
(From: Gavin Parrish (firstname.lastname@example.org).)
Kano Labs makes a number of exceptional products which are only available directly through them. They are not cheap, but all that I have tried have met or exceeded my expectations. Their premier product is "KROIL" a penetrating oil that breaches a space as small as one millionth inch. No fooling! Throw away that WD whatever-its-called stuff. If it's stuck, this will unstick it.
While they have a lot of really big industrial customers, they give attentive service even if you only buy 1 can. The only drawback is they keep sending you somewhat amusing flyers every month or so. You already get a lot of this so it's no big deal.
For info or ordering contact: (what? no URL?!): Kano Laboratories, 1000 Thompson Ln., Nashville, TN 37211-2627. Phone: 1-615-833-4101, Fax: 1-615-833-5790.
(The above is not a paid promotion, merely data I hope you find useful.)
(From: Rich Grise (email@example.com).)
Which solvent to use depends on what you're trying to dissolve. For a something like a cruddy motor, I'd try, in order from least aggressive up:
The chlorinated/fluorinated solvents sit somewhere in the middle of the range - someone else pointed out the difference between trichloroethylene and trichloroethane; I guess TCA is much friendlier than TCE - but we used them in the Airforce to clean up hydraulic fluids that nothing else would even touch.
I've heard that Vaseline makes a superb lubricant for bike bearings; it also makes a reasonable vacuum seal, and it's incredibly tenacious - one day, I used it on a gasket, and when I needed to make a change, I couldn't find anything in the shop that would clean it up completely.
Don't use WD-40 as a cleaner; it gums everything up. I inherited an old Baudot teletype once and thought I'd clean it with a WD-40 spray. HAH! Spent the next week disassembling the thing and cleaning all the gunk off the intricate little parts with TCA or something. WD-40 is good for door hinges.
Carburetor cleaner is a mixture of solvents in a spray can which may include acetone, toluene and methanol but it's extremely flammable and it seems to wash greasy dirt away as if it weren't even there.
Ordinary silicone window and bathtub caulk has the right mechanical and electrical properties (tough, flexible, excellent insulator especially for high voltage), but it secretes acetic acid upon curing and this may damage the electronic circuitry (but not always the case). Some types claim to be safe for this or that (e.g., aluminum) but unless it states specifically that it is safe for electronics, use at your own risk.
(From: Ralph L. (firstname.lastname@example.org).)
You can also use an RTV that is safe for oxygen sensors that are used on most computer controlled cars. It does not produce that acetic acid (vinegar smell) during the curing process and will not harm electronics.
(From: Greg Szekeres (email@example.com).)
Yes, Permatex Ultra Blue is safe, available at most auto parts stores. I have also been using polyurethane instead of silicone, although is has problems with some materials.
(From: RadMan (firstname.lastname@example.org)).
Some agents require UV to cure, some need heat. You can also try Miller-Stevensen 907 available at Future/Active, and it pots with a heat gun very fast (30 minutess).
(From: Bob Wilson (email@example.com).)
Dexter makes Hysol Epoxy which is a potting compound that totally encapsulates the circuits. There are easily available commercial coloring compounds intended for this purpose, and are available from the supplier of the Epoxy. An alternative is to mix some laser copier toner (dry powder) with the epoxy if making it opaque is desired.
Mind you, all that potting does as a means of security, is to keep he amateurs out. Depotting an electronic assembly is pretty easy. All that is needed is judicious application of a small welding torch flame to locally heat the epoxy above its glass temperature (whereupon it becomes rather "crunchy" and easy to remove), and a little patience.
(From: Brian Symons (firstname.lastname@example.org).)
The products normally safe to use are labeled "neutral cure" or at least they are here in Australia.
Any acid cure product is certainly dangerous around electronics. I cam across some PCB's that had had the wires glued in place by a run of acid cure silastic across the board.
When looking for the fault, I peeled up the silastic and found every track under the silastic was completely eaten away.
BTW. Over here, It is quite common for ovens to have a from glass viewing window that is glued in position with a silastic material that can handle the high temps.
When a warrantee guy ordered in a tube of the silastic, they supplied a tube of the silastic that is available here at car parts suppliers and service stations to repair windscreen seals. They were only charging about eight times the price though. This silastic is a black product. I have used it successfully for oven glass repairs for several years.
A good source for many of the basic parts is dead equipment - their organs can live on at your workbench. Parts like small resistors are so inexpensive that this doesn't warrant a lot of time. However, power resistors, potentiometers, power semiconductors, some ICs, etc. are well worth saving. Used electrolytic capacitors will generally still be functional but these do deteriorate with time and heat so testing them first and avoiding the use of really old ones for the permanent repair is probably wise. The majority of my parts inventory is from salvage. Think of them as 'pre-owned burned in components' :-).
Note that there are quite a variety of what we call "plastics". An adhesive that bonds with extreme strength to one may not even stick at all to another. (Nylon and polyethylene are difficult to glue; styrene is easy.) This is especially true of the 'welding' adhesives like MEK.
However, using the most appropriate glue can make a very significant difference:
WARNING: The vapors from all of these adhesives are harmful to health if inhaled. Work only in a well ventilated area.
CAUTION: Spills from some of these will also damage paint and other plastic surfaces (including eyegless lenses!) even if wiped up immediately.
Where possible, I add reinforcement to plastic parts - either with plastic or metal. Or, fabricate all metal replacements. I've heard of people successfully adding bits of metal to replace plastic gear teeth. I have several clock radios with a mechanical clock where the little plastic pin in the number changing mechanism invariably broke after 5 years or so on all similar models. I replace them with a piece of steel wire (from a large paper clip) glued in place. This repair has worked for over 20 years. I bet the manufacturer saved a fraction of cent on each unit though! And, when someone forebly removed a paper jam on an HP DJ1000 printer and broke several pressure roller spring levers, stiff steel wire came to the rescue once again.
For those of you without Web access at home or work, this may not sound like good news. However, libraries and other institutions are increasingly providing this service, and one can't hide from the future forever!
PCs have been of this type for many years where anything beyond swapping modules is probably a futile exercise. Well, guess what? Devices lie digital set-top boxes, digital video recorders, video game consoles, and digital flat-screen TVs can be added to this list. Except, that they aren't going to use anything resembling standard modules like PCs still do to some extent. So, forget about achieving any significant success rate repairing this and similar equipment.
How do you determine the actual manufacturer? For most types of consumer electronic equipment, there is something called an 'FCC ID' or 'FCC number'. Any type of equipment that may produce RF interference or be affected by this is required to be registered with the FCC. This number can be used to identify the actual manufacturer of the equipment.
A cross reference and other links can be found at:
Sams' Photofacts schematics and service literature are published by:
These folders of service information have been published for over 45 years (I don't know for how long but I have a set for a 1949 portable 3 inch Pilot TV - about as portable as an office typewriter if you remember what one of those was like) and are generally the best most consistent source of service info for TVs, radios, some VCRs and other consumer electronics. There are some Computerfacts but the number of these is very limited. The VCRfacts are also somewhat limited and the newer ones tend to have strictly mechanical information.
Even if they don't list your model, they may have a folder for one using the same chassis so search by chassis number as well. Even if this doesn't help, there still may be a folder for models that are similar enough to be of value (though you really have to be in the library to be able to determine this by looking at the circuit diagrams or photos) so check out folders for other model numbers that are close to the one you really want.
Sams' Photofacts are often available (for photocopy costs) from you local large public library which may subscribe to the complete series. If not, a large electronic distributor can order the selected folder for you.
One advantage of the Sams' info is that it is compiled in a very consistent format so that once you are familiar with one model TV, it is easy to transfer that knowledge to any other. They provide waveforms at key locations and DC voltage measurements almost everywhere. Additional info such as IC pin to ground and coil resistances are often provided as well. The manufacturer's service manuals are generally not nearly as complete.
Note: I have heard that some of the Photofacts recently purchased directly from Sams Technical Publishing/Howard Sams have been poor photocopies with illegible scope waveforms rather than original printings. If this is the case, it is truly the end of an era and too bad. In any case, try to confirm the quality before you buy or get your info from the library.
Microwave ovens do almost always have a schematic diagram of the microwave power generation circuitry pasted inside the sheetmetal cover. This will generally include at least the high voltage transformer, interlocks, rectifier, capacitor, and magnetron. Since most microwave oven problems are in these areas, this is all you are likely to need. The controller, especially electronic units, is often omitted or only covered superficially.
As of Winter, 2002, I have confirmed that all the following Web sites for manuals and schematics are active. However, I have NOT checked email or snail mail addresses. Note that since these sorts of sites come and go, I'd advise downloading and archiving whatever you might possibly need when you find them - don't just save the links. You may be sorry later!
Listed in more or less alphabetical order:
For Heathkit manuals specifically:
(From: William E. Miller (email@example.com).)
Besides the used Sams TV Repair Manuals I sell, here are a few good sources for various flavors of service manuals.
"Parts and Service Data, 1920s to the present". Lotsa stuff!
Sams Photofacts and service manuals for older TVs, stereos, and radios, as well as test equipment, vacuum tubes, electronics books, and magazines.
(From: Mike Kaufman (firstname.lastname@example.org).)
"This is an excellent source for very reasonably priced repair manuals, especially out-of-date manuals,. Michelle's prices are on the order of $2.50 per manual plus $1.50 shipping - hard to beat."
He has a LOT of AUDIO service manuals for sale. Check his full list at his web site.
"We will be happy to help anyone who needs a schematic or parts breakdown for virtually any make and model (commercial or residential) microwave oven."
"Suppliers of Technical Books and Servicing Information to the television, video and computer repair trade"
The U.S. Military has an extensive library of test equipment and related manuals, some of which are in the public domain:
(From: Dino (email@example.com).)
Go to: U.S. Army Logistics Support Activity. Select "Publications and Forms" which should get you to LOGSA Publications and Forums. Then select "Electronic Technical Manuals Online" which will roll you down to "Go to Electronic Technical Manuals Online". Click on this link which takes you to http://www.logsa.army.mil/etms/online.htm. If you accept their terms, click on "I accept" which takes you to http://www.logsa.army.mil/etms/welcom1.htm Choose "Enter the Site" [Note the disclaimer that you have to login if accessing anything but public release manuals and that you have to have 128 bit encryption engaged. That should bring you to: http://www.logsa.army.mil/etms/find_etm.cfm. which is the search page; click on "TM Title Text" and enter, for example, "Tektronix" and scroll down to hit "Search" which should get you to: http://www.logsa.army.mil/etms/show_etm.cfm where if you scroll down and look CAREFULLY you'll find lots of material in .PDF format which you can then download.
You may have to go through this entire process to establish the fact that you accept their terms. There's probably a cookie in my system that lets me go straight to the search page. I've found a number of good references here for text equipment.
I use a source in Canada for cheap schematics. I have to mention that they have limited coverage in the last while due to some O.E.M. holdbacks. There is nothing at all on monitors. It is:
What they do cover is inexpensive, typically 5 schematics + data in one $19.50 manual ($14.00 U.S.). An example, I just received a manual the other day that I ordered to service a Sony VCR. It contained the following.
I suggest ordering their master index. They have 2 of them, pre-1973 and 1973 to present. You will need it for crossing anyway and it will give you a better idea what value their resources will be to you. Cost for an index is $5.00 (Can).
I have no idea of their cost, reliability, quality, or accuracy but this type of source may be worth checking if you are desperate! One risk is that he wants $5 for catalogs of at most 3 categories from the following before you can order: audio, auto/air/marine, computer, detection, industrial, lighting, medical, phone, power supplies, radar, radio, security, tape/disk, telemetry, television, test equipment, time, toys & games, video, potpourri (misc).
Here is another company which has some reverse engineered schematics:
They have some PS/2 and other PC and monitor related schematics but not nearly the selections it would seem as Bomarc, above. I do not know anything more about this company.
(From: Jeff Zurkow (firstname.lastname@example.org).)
Here's a trick I'm using for reverse engineering: Put the board on a color photocopier, set the copier for "mirror image", and make a copy. This gets you a top view of the underside, as if the board were transparent. You can tape a piece of drafting mylar over the copy, and draw in the topside components and traces with colored pencils. In fact, I sometimes use multiple mylars: top traces on one, components on another, component values on a third, and a final one on which I check off components and solder joints as I draw them on the schematic. It helps to have a light box :)
The layered drawing can also serve as a component-location key for future troubleshooting. Just assign new component identifiers (the ones silk-screened on the board are often obscured by the components), and draw them in on both the mylar and the schematic. Makes it real easy go from the schematic back to the circuit board.
Take the lowly 2N3055 power transistor, for example.... (Most of us have its specs engraved on some radiation-hardened neurons safely tucked away in a forgotten part of our brains but for the freshly minted EE or technician....
(From: Mark Zenier (email@example.com).)
Places to look:
The web, at sites for companies that make power transistors.
Good bets would be Motorola (http://www.motorola.com/), Philips (http://www.semiconductors.philips.com/) Note: only 1 'L' in Philips, and SGS-Thomson (http://www.st.com/). (A whole bunch more people make 2N3055s, down to some little 50 employee companies that you've never heard of, but they may not have a web site yet). Or start with one of the web directories like http://www.xs4all.nl/~ganswijk/chipdir or Grey Creagers pages on http://www.scruznet.com/~gcreager. (Hope I got my spelling right on all those URLs).
The sales rep, sales office, or company literature department. Look in the phone book or on the web page for the phone number of a company or their local or regional sale representative or office. Call them up and ask. It's their job to provide customer support and if you sound like you halfway know what you're doing (saying you're a student works, too) AND it doesn't cost them much (don't get greedy) they'll often be more than willing to send you information. (These days, it might be a CD-ROM of their whole product line. Cheap, but not that easy to use, IMHO.) If they won't help you, ask them where there is someone who can. Like the nearest distributor.
Electronics distributors. Larger ones often fill the same literature distribution role as the sales rep. Other distributors like Jameco, JDR Microdevices, Future Active sell databooks as a catalog item. Or a local distributor that caters to the walk in trade will have a databook shelf and allow (or have a nominal fee for) photocopies. (The big distributors are closed operations, mostly using phone salesmen and UPS for distribution, visitors aren't necessarily welcome.)
A good library. Like one at a university with an electrical engineering program, or a large city library.
Used book stores, a big unselective 'book dump' often will have a good stock of old databooks. Ones that you can't get from the manufacturer and more. Likewise, electronics surplus stores (most big cities should still have one or two) often have them.
Also see the section: House Numbers.
Here is the current Web site for NTE:
(From: Gregg (firstname.lastname@example.org).)
"NTE's device numbers are the same as ECG's, and their cross-ref guide can be downloaded from http://www.nteinc.com/.
It's free but they do want you to register. If you want to bypass this, go to ftp://nteinc.com/pub/ and download the windows version of the guide, ntesetup.exe. Don't bother with the dos version; the file named dosdisk2.exe is bad, and won't unzip."
I am not necessarily recommending using NTE (or other generic) replacements if the original replacements are (1) readily available and (2) reasonably priced. (Note that very often the original replacement part will be less expensive than the equivalent from NTE. Therefore, it should be used if available.) However, the cross reference can save countless hours searching through databooks, seaching the Web, or contacting the manufacturers. Even if you have a wall of databooks, this source is invaluable. However, there are a couple of caveats:
I often use the replacement guide to determine upper bound specs but as noted above, rarely buy any generic parts (sorry NTE). Then I find industry standard parts that have equal or better specs. Dalbani's catalog (see the section: Mail Order Parts Sources) has a sort of inverse cross-reference from NTE to 2S/2N/BU/whatever that isn't a bad starting point (though probably not to be trusted without confirmation of actual specs). Of course, this doesn't necessarily help with some tricky HOTs and choppers....
Note that while Howard Sams of Sams' Photofact fame publishes a semiconductor cross reference manual (or used to), it would appear to just be a compilation of the ECG, NTE, SK, and Radio Shack manuals - and much more expensive ($25 or so).
For standard ICs, IC Master can often provide quick access to complete data. Full access to their Web site is currently free but they do require registration. However, with their print version, ICs no longer manufactured were not listed. I assume the on-line version will be similar. Thus, it may be of only limited value for older equipment.
There are many other '2S' prefixes but these are by far the most common.
Suffixes may denote package type or some special feature like an internal damper diode (D, for horizontal output deflection transistors), enhanced gain, special speed sort, etc.
A cross reference of sorts is availabe at Transistors Japonais (French). Don't worry, the device numbers are the same in French and English. :)
There may be other examples but these are the exceptions (at least for now).
(From: Mark Robinson (mark-r@snow_white.ee.man.ac.uk).)
We are lucky with transistors that, apart from a few oddities which I'll talk about later, most markings follow one of these codes. ICs are more tricky as you're often dealing with custom chips or mask programmed devices with manufacturers individual codes. A quick hint though: always look for known numbers (e.g., 723, 6502, 2764) etc. between the suffix and prefix, and beware of the date code.
Right... Back to transistors. The three standard transistor marking schemes are:
These take the form:
where the letter is always 'N'.
The first digit is one less than the number of legs, (2 for transistors unless they're crippled although I'm not sure about 4 legged transistors maybe they get a 3) except for 4N and 5N which are reserved for optocouplers.
The serial number runs from 100 to 9999 and tell nothing about the transistor except its approximate time of introduction.
The (optional) suffix indicates the gain (hfe) group of the device:
See the data sheet for the actual gain spread and groupings. The reason for gain grouping is that the low gain devices are fractionally cheaper than the high gain devices, resulting in savings for high volume users.
Examples: 2N3819, 2N2221A, 2N904.
These take the form:
Again, the digit is one less than the number of legs.
The letters indicate the application area and flavour of the device according to the following code:
The serial number runs from 10 to 9999.
The (optional) suffix indicates that the type is approved for use by various Japanese organizations.
NOTE. since the code for transistors always begins with 2S, it is sometimes (more often than not is seems) omitted so, for example, a 2SC733 would be marked C733.
Examples: 2SA1187, 2SB646, 2SC733.
These take the form:
The first letter indicates the material:
Needless to say the biggest majority of transistors begin with a B.
The second letter indicates the device application:
The third letter indicates that the device is intended for industrial or professional rather than commercial applications. It is usually a W,X,Y or Z.
The serial number runs from 100-9999.
The suffix indicates the gain grouping, as for JEDEC.
Examples: BC108A, BAW68, BF239, BFY51.
Apart from JEDEC, JIS and Pro-electron, manufacturers often introduce their own types, for commercial reasons (ie to get their name into the code) or to emphasize that the range belongs to a specialist application.
Some common brand specific prefixes are:
Examples: ZTX302, TIP31A, MJE3055, TIS43.
Many manufacturers also make custom parts for large volume OEM use. These parts are optimized for use in a given part of a given circuit. They usually just have a manufacturers stamp and an untraceable number. Often when a company goes bankrupt, or has surplus at the end of a production run, these transistors find their way into hobbyist bargain packs. There is no way that you can trace data on these devices, so they are only suitable as LED drivers, buffers, etc, where the actual parameters are not important. Check carefully before buying.
Once you have identified your part, a trip to the data sheet or equivalents book is called for (anyone know of an on-line equivalents list?).
The Web sites of semiconductor manufacturers may also have some information but this varies widely from company to company.
There is an on-line list at:
This is also somewhat incomplete. And, a very nice one at:
There used to be SMT marking codes info at:
However, since the semiconductor division changed their name to Infineon, I haven't been able to locate the page if it exists.
Are house numbers used just to make life difficult?
It certainly seems that way from the perspective of repair. Give me industry standard numbers anyday. However, house numbers are a fact of life.
The house number is what you need to order a replacement from the original manufacturer of the equipment but that may not always be desirable due to the likely high cost and possible difficulty in locating a suitable distributor that carries the manufacturer's replacement parts.
As noted in the section: "Parts information and cross references", a Master Selection Guide like NTE may be able to give you some idea of the specifications even if you don't want to use their generic replacement semiconductors. Their web sites have (or should have in the future) some amount of cross reference information for industry standard and house numbers. However, don't expect to detailed IC specifications or even pinouts in most cases there or from the disks they may also offer. The hard-copy Master Selection Guides which these companies sell have been better in the past (though this may be changing) but even these won't give you all the details. However, if you do repair work regularly, these 'telephone book' thickness guides worth the few bucks that is charged.
Also see the section: Parts Information and Cross References.
Other common components including flyback transformers, belts and other rubber parts, and RF modulators may also be available from these sources but they tend to be used less often and quality may vary even more.
There are some other similar companies like SK (part of Thomson Consumer Electronics) but NTE now appears to dominate the industry for these generic replacement semiconductor and other electronics components.
This will help decode all those odd 1820-xxx numbers!
Also HP and Tek repair parts and equipment on line, plus helpful FAQs and links to all kinds of test gear sites.
We also have a big used equipment site on line for Canadians.
Tandy (Radio Shack) has a nice web resource and fax-back service. This is mostly for their equipment but some of it applies to other brands and there are diagrams which may be useful for other manufacturers' VCRs, TVs, CD players, camcorders, remote controls, and other devices. The Tandy Product Support Page has links to each type of equipment.
In addition to Tandy products, there are a couple Sony models. Furthermore, since Tandy does not manufacture its own TVs, VCRs or camcorders - they are other brands with Realistic or other Radio Shack logos - your model may actually be covered. It may just take a little searching to find it.
You are searching for the Holy Grail. Everyone is, but it isn't going to happen on a large scale - at least not for free. Schematics are copyrighted by the equipment manufacturers who sell them as part of their service manuals or license them to organizations like Sams Technical Publishing (Sams' Photofacts) and others.
That is my take, at least.
Having said that, there are many Web sites with schematics that may or may not have been legally copied and made publicly available. See the section: Additional Sources for Service Information and Manuals.
To paraphrase a famous quote: 'The only stupid or useless information is that which is not provided'. However, unless you really are sure of what you are talking about, don't try to tell the repair person what you think the problem is likely to be. Don't bombard them with technobabble full of buzzwords - any competent tech will see right through that. You can be sure that if you mention that you suspect the expensive flyback is toast, it will be diagnosed as bad. Let them do their job. Listen carefully to their diagnosis. You should be able to tell if it makes sense.
There is an excellent chance that your question has come up and resulted in information being passed back and forth on sci.electronics.repair (or other appropriate newsgroup). For example, if you have had problems with a late model RCA/GE television, there have been dozens if not hundreds of postings on this subject over the last couple of years. There is no need to add to the clutter.
Google Groups (formerly Deja.com/DejaNews) includes a USENET newsgroup searching facility. It has been archiving newsgroup articles since March, 1995. By going to their web site, you can invoke a search of over 45,000 newsgroups (hundreds of GB of data!) for any set of words, names, or email addresses. Within *seconds*, they will provide a list of postings that satisfy your search criteria. Try using Google Groups at least once - you will be instantly hooked. :( Some of the relevant site URLs are:
While postings typically drop off of your local server in a few days or less, Googlegroups maintains them *forever* so that locating an entire thread becomes a trivial exercise in identifying a search string that will narrow down the postings to those relevant to your needs.
There are many other services available via Google Groups including newsgroup posting (under constructio apparently during the transition from Deja.com).
Speaking of posting:
Even if your ISP doesn't provide USENET newsgroups or allow posting for some reason, you can always access them (read, search, and post) via Google Groups. See the section: Searching for Information from USENET Newsgroups.
No matter how you do it, however, here are some tips that will get you what you want without unnecessary flame wars:
The FAQs can be found at:
and its mirror sites. First read the README and Mirrors links to identify the best way for you to access the information from your location.
For numerous examples of ASCII schematics that should look fine, see: Various Schematics and Diagrams.
Large binary files are not supposed to be posted on these newsgroups. In addition, you will upset people who are forced to download a 1 MB file they have no interest in but may not know it until they see the description. Some ISPs charge for connect time and bits transferred. If you have a large scanned schematic and you think it really will help with a diagnosis of or solution to your problem, offer it via email, upload it to your Web site, or post it to the newsgroup: alt.binaries.schematics.electronic (but not all news servers carry this group).
More importantly for you, receiving replies via email will circumvent one of the most important functions of the newsgroup - cross-checking to locate errors in responses either because the responder didn't know what they were talking about or made an error in interpretation. Perhaps, they were just being a bozo and sent a totally bogus or even dangerous response. And, some people may have hidden agendas that aren't in your best interests. If that was the only reply, you would never know. While there is a lot of high quality information available via the Internet, there is also a lot of noise. Yes, you will need to read the newsgroup for a few days. That will be a small sacrifice and well worth the effort.
If your news feed is indeed poor - as many are - and you are honestly afraid of missing the responses, then phrase your request for an email reply in such a way that it doesn't sound like you are totally immature and lazy.
Another alternative is to search for replies at:
This service will enable you to search for only the postings you are interested in and seems to be pretty reliable. They subscribe to a half dozen news feeds just to avoid missing *your* postings!
Many people will send you a CC of their posting anyhow so avoid getting flamed for poor netiquette. However, take note below.
It is very annoying to reply via email only to find that the same question appears a little later on the newsgroup requiring a repeat response.
In any case, once your problem has been resolved (or you have given up), it is polite to post a concise summary of the problem, suggestions, the solution or frustration, and appreciation to those who have helped you.
There are also a few repair related email listservers. These require that you subscribe by sending a special email message and/or filling out a form. Some may have merit in that experts are more likely to be subscribers and they are forced to at least receive all emails (even the next stop is the bit bucket!).
Sorry, given the relatively low interest in both private discussion groups and email listservers, I can't justify attempting to keep up with their arrivals and departures! :) Both of these can be found through the various tech-tips sites as well as by searching postings on the Sci.Electronics.Repair Newsgroup via Deja.com. A few may also be listed in my Bookmark File.
Having said that, popular services like Yahoo often host at least a few niche discussion groups that simply due to the number of users, have a volume of traffic worth noting. For example, go to Yahoo Groups and search for "Tektronix". Two groups for Tektronix oscilloscopes will pop up, one for general postings and the other for documentation like schematics.
(From: Rex (email@example.com).)
I have been asked to give tips for dealing with repair shops. It is sometimes difficult for the average consumer to convey their needs to shops or technicians.
Avoid getting into dialog about children, grandchildren, holidays, bad mouthing other shops or manufactures, "I can get a new one for that", vacations, school functions, how seldom you have used the product or anything that that has nothing to do with you product's failure.
CAUTION: Be VERY sure what the warranty is. Most repairs are covered for the work done, not the entire operation of the product. Read the shop warranty and ASK questions.
However, none of these places have even the most basic service parts for consumer electronic equipment. You won't find a single rubber belt, RF modulator, posistor, or video head, nor most Japanese semiconductors within their thick catalogs.
It may be possible to go direct to the manufacturer of the equipment but expect to spend many times the true price of a part to get it from the horses mouth. In most cases, a totally identical part - with the manufacturer's logo and everything - meeting identical specifications is available elsewhere at a fraction of this cost.
In addition, Tandy, the parent company of Radio Shack is worldwide and may actually offer a USEFUL selection of components:
(From Ted Gondert (firstname.lastname@example.org).)
Tandy (aka Radio Shack) has a new catalog available at your local Radio Shack; "Tech America" "Your Electronics Resource". This is special mail order catalog with many parts available from a different division of Tandy. There is no minimum order and parts are sent directly to your house. Shipping is $4.00 for components orders only or various rates up to $13 for orders of $500.
Call 1-800-877-0072 between 7 a.m. to 11 p.m. M-F Central Time, 9 a.m. to 8 p.m. Saturday, 11 a.m. to 7 p.m. Sunday. Fax 1 800 813-0087. Mail: Tech America, PO BOX 1981 Fort Worth, Texas 76101-1981.
This catalog, Sept 1997 has 546 pages with capacitors, resistors, transistors, IC, coils, wires, antennas, test equipment, tools, radios, security equipment, books, etc.
The capacitors include high temperature, 105C electrolytics. The integrated circuits and transistors are mostly American type part numbers, digital, op-amps, etc. not the Japanese type used in most consumer electronics today. But should be many parts that electronics techs can use.
For example; 1000ufd 16 volt 105C electrolytic capacitor is only 39 cents. (pg 14) That's popular size in use in Panasonic SMPS. Also has MJ15024 audio output transistor for $4.59 (pg 49) and surface mount transistors.
Radio Shack also has catalogs in stores for RSU, Radio Shack Unlimited. Those show Japanese semiconductors, special batteries, phono stylus, equipment, etc. that your local Radio Shack can order.
(I haven't ordered anything yet but after checking my inventory and budget will probably stock up on some capacitors, etc. Get most of my parts from MCM, MAT Electronics, etc and some local distributors.)
Any intermittent problems with monitors that cause random sudden changes in the picture brightness, color, size, or position are often a result of bad connections. Strategically placed bad connections can also cause parts to blow. For example, a bad connection to the SCR anode in a phase controlled power supply can result in all the current passing through the startup resistor, blowing it as well as other components. I had a TV like this - the real problem was a bad solder joint at a pin on the flyback. Thus, erratic problems, especially where they are power or deflection related, should not be ignored!
Bad solder joints are very common in TVs and monitors due both to poor quality manufacturing as well as to deterioration of the solder bond after numerous thermal cycles and components running at high temperature. Without knowing anything about the circuitry, it is usually possible to cure these problems by locating all bad solder connections and cleaning and reseating internal connectors. The term 'cold solder joint' strictly refers to a solder connection that was either not heated enough during manufacturing, was cooled too quickly, or where part pins were moved before the solder had a chance to solidify. A similar situation can develop over time with thermal cycling where parts are not properly fastened and are essentially being held in by the solder alone. Both situations are most common with the pins of large components like transformers, power transistors and power resistors, and large connectors. The pins of the components have a large thermal mass and may not get hot enough during manufacturing. Also, they are relatively massive and may flex the connection due to vibration or thermal expansion and contraction.
The Sony and RCA/GE tuner shield problem is interesting because this could have been solved years ago at essentially no additional cost as other manufacturers - and their own repair procedures - have proven.
The most common external causes would be electro-magnetic interference, either through the air or via the power line. For more on these in particalur, see information on interference in the documents on TV and monitor repair. But, suffice it to say, changing the location or electrical power source will usually help to narrow it down.
If internal, it may be physical, heat related, or mode related. Gentle whacking (yes, whacking is an acceptable diagnostic technique but don't go for the 12 pound hammer!), pressing, flexing, cable wiggling, etc., can and should be used in an attempt to confirm at least that there is a physical cause inside the unit. Doing these tests just as the problem comes or goes is the best time as whatever is marginal, will be most marginal then.
If the problem appears or disappears, or does both, over a period of time after the equipment is turned on, then temperature is almost certainly a factor as the circuit board and components expand.
The most common physical problems are bad (cold) solder joints, connectors that need to be cleaned and reseated, and bad cables or cable connections. Perhaps surprisingly, though components may fail internally and result in erratic behavior, this is probably lower on the list of likely causes than those listed above. Some exceptions would be mechanical relays in audio power amplifiers, phone equipment, and elsewhere; hybrid power amplifiers, and other power devices.
The whacking, etc., can be done without taking the cover off the equipment and may or may not reveal anything. In either case, you will have to go inside. But if there is an effect, then you will know that the problem IS inside and further tests will need to be done to identify the specific cause.
Once the cover is off, there still may be quite a challenge to find the specific solder connection or contact that needs attention. Knowing something about how the actual circuit area relates to the symptoms will help narrow it down. For example, if there is a loss of vertical deflection in a TV or computer monitor, the most likely areas to attack will be the vertical deflection output stage and its power supply feed.
For popular consumer electronic equipment, intermittent problems are often present in many (or even most) samples of a particular model over the course of its life. Therefore, checking a tech-tips database or asking on the USENET newsgroup sci.electronics.repair may reveal a common cause and an easy solution ("resolder the flyback pins"). There are a list of tech-tips databases at my Web site, www.repairfaq.org.
(From: Phil Buble N1GTZ (email@example.com).)
A note on whacking as a troubleshooting technique, at home and in the shop.
I'm not what you would call a full time electronic repairman though I have made a living doing it commercially. I can be just helping a friend out at home but usually it's been an adjunct to my main work as assembler/post flow touch-up and I'm pretty good at it. Therefore most of my repair experience is with new equipment that doesn't work correctly the very first time it's powered on. (and yes when *will* that wave-solder machine learn to solder? :) Running that thing is a art-form I'm glad to avoid)
Naturally in such a situation I'm a great believer in "swap-out with NGP testing" since there's usually lots of them in an assembly shop but this cannot always be easily done. Especially at home, with obsolete units or those so small or cheaply made not a vacuum tube, IC or module is to be found in a socket. My funniest experiences with whacking regard these - one commercially and one at home. The commercial one first:
It involved a totally obsolete and smallish sensor board used in the ground-water monitoring industry to measure water pH deep down in wells. Even carefully sealed you can imagine the condition it was in after years of hard use. Only a few had ever been made by the company long before and the engineer who designed it equally long gone. A young, recently hired engineer was given the task of finding out what was wrong. It was giving rather useless and erratic readings and needed to be repaired in a hurry. I cleaned it and reflowed all joints, just in case, then turned it over to him since it still didn't work. After hours of frustration and attempts to get "into the head of the designer" he gave up and I asked to give it a try. By then I had a hunch. I made a routine test to make sure all was getting power - then gave the PCB a whack and a little twisting action. It began working perfectly as long as the PCB had a slight twist to the right. This literally took me all of about 5 minutes. You have never seen such a dumb-founded engineer! They do need to get out more! Even with the failure mode detected the cracked trace could not be found in a reasonable time so I had the honor of transferring all the parts to a new PCB. Amazing they even had one.
The second funny situation occurred many years before the above and happened at home. A neighbor brought over a old (even for the time) but nice condition 19" tube-type B/W TV hoping I could fix it. Fully half this set was point-to-point wiring, no PCBs at all. I'm old enough to have one foot in the all tube and "condenser" era and one foot in the transistorized world so it didn't matter to me that it was tubes. As long as my friends are willing to pay for the parts and hopefully locate a schematic I'm willing to at least try. It's all done in a casual sort of way. (Side note: You'll have to pry my Heathkit AA-100 Vacuum Tube Stereo Amp from my cold dead hands, it still sounds great 41 years after it was built)
This one located the Sam's Photofacts for it, complete with schematic and pin voltages. A resistor in the B+ line to the plate of the Horizontal output tube had burned out. That was replaced and all DC pin voltages then looked OK - yet no picture. Sure, the H Oscillator wasn't oscillating! The next logical thing to do was to swap-out the H output tube with another to see what happened. I told my neighbor we needed to locate a tube, and a rather expensive one, to go any further. He didn't bother, it wasn't worth the effort or expense. 5 *YEARS* later he trots out that same TV hoping, once again, I could get it to work. I tell him we still needed that tube. He shrugs, plugs it in, turns it on and gives it a good whack. It came on and worked perfectly! That's all it needed all along, my power-supply repair had fixed it 5 years before but no one ever whacked it to get it started again.
Selective circuit whacking's been one of my most productive and time saving
Make the inspection under a bright light. If your closeup vision isn't perfect, use a good magnifier - these may literally be hairline cracks and their visibility may be obscured by reflections from the solder joint. Use a pointed stick (not something metal if possible) to gently prod any suspicious looking pins to see if they move. Look for discolored patches on the circuit board. Such discoloration isn't in itself a problem unless it is severe but indicates that hot components live there or nearby and bad solder joints are very likely.
Once a particularly sensitive area is located, use a stick thin enough to just touch a single pin at a time. Sometimes, a probe with a pointed metal tip, insulated for all but the last 1/16" or so, will be useful as it can get into the area between the pin and solder pad where cracks may have developed but are not visible. The metal tip will bridge the gap causing a change in behavior.
For a TV or monitor, point the camera at the CRT and the scope screen so that they are both in the picture and record on a 6 hour tape. Then, when your event takes place, you have a permanent record!
That old video camera will be perfectly adequate. It doesn't need a 100X digitally stabilized enhanced reprocessed zoom or 1/10,000th second shutter. It doesn't even need to be color!
Sure, this won't capture the 1 ns glitch. But, for the occasional flash in the picture, it is more than adequate to eliminate a video signal line as the source of the problem.
Now the question comes up: How can the re-occurrence of intermittents be prevented? For cracked solder joints, in addition to using proper soldering techniques for repair, it should be possible to add some "reinforcements" in the form of bare wire wrapped around the pin and extending out to the circuit board trace or even to an adjacent component pin. This will be better than just using more solder. For the CTC175 etc. cases discussed below, there is also special "elastic" solder that supposedly should be used. But, there are mixed reviews on whether this really helps.
Some equipment may also benefit from a small amount of additional cooling. A small fan can be added to draw air out of the cabinet. This will improve reliability since most components are happier being cool but will also reduce the extent of the thermal cycles reducing the likelihood of bad solder joints developing in the future.
Some Sony TVs suffered from a similar set of bad solder joints, usually in the tuner or IF (metal) boxes. The most common location for the problem for many of these was to one pin of a coil inside the IF box which always seemed to lack adequate solder.
Much more information on the RCA/GE/Proscan and Sony solder problems and solutions, see the documents: RCA/GE TV CTC175-187+ Solder Connection and EEPROM Problems and Sony TV Tuner and IF Solder Connection Problems.
Other makes and models of TVs have similar problems with solder joints but not to the extent of these.
Always check to see that you got all the accessories - remote controls, cables, attachments, etc. Often, they will have long since disappeared but it won't hurt to ask.
Try to find out what the symptoms were from the owner if possible. With a little knowledge, this could improve your bargening position as well - or make you decide to try for a lesser challenge:
"Jonny stuck a peanut-butter-and-jelly sandwich in the tape slot and when his pet hamster wen't to eat the sandwich it got stuck. They have both been there for a couple of years now. I put the VCR in this plastic bag to protect it from moisture. It really is a great VCR".
"Well, there was this lightning strike, the modem exploded and 6 foot flames leaped out of the monitor so I dumped a pitcher of lemonade on it to put out the fire. What is left of the PC is still melted to the floor but I figured someone could use the monitor."
I would skip those.
Another high risk would be a piece of equipment that had been worked on by someone not competent to change a light bulb:
"My VCR wouldn't play my Rambo tape so I opened it up and found this silver thing was out of line - you know, all cockeyed. So I tried to straighten it with a pair of Vise Grips(tm) but I must not have done it quite right as now all I get is snow and it makes these crunching noises. Maybe you will have more luck"
"I tried to repair this amplifier but while I was making some adjustments, my screwdriver slipped and there were these HUGE sparks and bubbles appeared on several of those black things that look like cochroaches and parts flew off of those clips glued to this plate at the back. You wanted a challenge, right?"
"Duh, I thought I would get cool music in my car but for some reason I cannot fathom, the jumper cables I used got really hot and my portable CD player now smells really bad and doesn't work on the normal transformer anymore. I will throw in the jumper cables for nothing."
I would pass on these as well.
In addition to melted or scorched cabinetry and the wonderful aroma of charred circuitry, look for the absense of cover screws and chisel or chainsaw marks!
I like to swoop in and swoop out - thus my preference for garage sales.
The most annoying situation is when after haggling over the price of a 'dead' VCR, you get it home with great expectations of the challenge ahead only to find that it works perfectly or your Mark-I thumb is all it takes to clean a supposedly trashed video head (but you do have to know the proper technique and incantations!) I ended up with a couple VCRs like that. A 'dead' CD player for $5 magically cured itself on the back of my 10 speed bicycle. Often problems are simple and easily remedied resulting in quick gratification. However, there will be real dogs which could more than make up for the easy fixes (like the GE TV with the never ending string of bad solder connections). At least, if you sell the easy ones, this will help pay for your 'habit'.
I do not know how viable an option this typically is since I have never tried it. (However, I used to trash pick mostly replaced vacuum tubes - nearly always tested good - back in those days when such things were common.) If they consider you a threat to their business, you may get the cold shoulder. If they consider you a future employee - or suspect you will make whatever you are working on worse and increase their business that way, you may be forced to take a whole pallet load of stuff off their hands :-).
Note that this could turn out to be very frustrating if by chance you end up with partially cannibalized equipment without realizing it. "This VCR does not load the tape around the video drum. Come to think of it, what happened to the video drum...?" Or, "There seems to be a big hole in the front of the TV. Now, what could possibly be missing...?"
Make friends with several local apartment superintendants When they clean house after someone moves, they toss out all kinds of working/non-working stuff the folks left behind. Some supers make a little extra cash by fixing and reselling this stuff, some just give it the heave-ho.
(From: Paul Grohe) firstname.lastname@example.org).)
Ah! If you are really serious about buying equipment, carry one of those little 200W 120VAC inverter bricks *with you* in your backpack, along with a cigarette socket to car battery clip adapter. Keep a small marine or gel-cell battery in your car (or with a friend who has a table).
This way, when you "roll up" on a good deal, ask the seller if you can borrow his cigarette lighter, or car battery, for a few minutes. If you can't use his car (and if you have time), run back and get your battery.
If he refuses...There's your answer!
I keep an 8-cell "AA" battery holder and an assortment of pigtail power connectors in my backpack. This way, I have an adjustable 1.5 to 12V power source to test things there on the spot (I'm planning on making a complete test box, complete with ammeter and current limiting).
I also carry a bunch of "AAA" and "C" cells in my backpack ("C" cells can be shimmed into "D" holders with a few coins between the batteries).
The same rule applies, If they won't let you test it.....etc,etc,etc.
Will they give you their business card or phone number? Make it clear you will not bother them unless absolutely necessary (secretly write down their license plate number, for "Justin Case").
Also carry a pocket DMM (This is a *must* for any flea enthusiast - NEVER buy batteries w/o testing them first!) and a small, bright flashlight (for "inspections").
Smell the equipment too! This can be a big clue as to it's condition. Does it smell like something blew up? Does it smell musty or moldy?
Another clue I have found is the physical condition of the unit. Sometimes the "cleanest" unit of the bunch is the one that failed prematurely and got stuffed on a shelf or back in the box. Whereas the "used looking" units were just taken out of service.
More importantly than "functional", is "complete".
Nuthin' worse than getting something and finding out a piece, or a board, or a module, or an expensive or rare IC is missing. Now you know it's not functional, and there may be little chance of it even becoming functional again.
I always assume "dead" until happily proven otherwise. Follow your instincts! If you have doubts, there's a reason! I always consider the scrap value of the item also. Any expensive goodies in it? The power switch may be worth more than the item!
Some of my best deals were the "I don't know if it works...Oh,..five bucks" deals.
It's a gamble...Ya' win some, ya' loose some!
(Let duh buyer beware!)
That's me! Flea Markets/Surplus Stores/Salvation Army/Goodwill/thrift
stores/Garage-yard Sales/etc...And there is *lots* of good stuff around
I call it "going' Junkin'".
I arrive at about 5:30 AM, so that requires a combo krypton
spotlight/fluorescent lamp flashlight (a $3 Goodwill special :^).
I carry with me the aforementioned 8 cell battery pack, 8 "C" batteries, a
bright krypton penlight, one of those all-in-one
screwdriver/knife/pliers/scissors/bottle opener contraptions ("fishermans
friend"?) and a small pocket DMM. All about 5-7 pounds total. I carry it
all in a backpack that I wear "backwards" on my chest (for easy access).
During the "lull" (around 9 AM), I go back and "load transfer" to the car.
I got it down to a science!! ;^)
After some lucky "scores", and a few *hundred* hours of troubleshooting, I
have a *very* well stocked home lab... :^)
My home lab is graced with a Tek 576 Curve tracer (bad Xfmr), HP 5345 Freq
cntr (bad NPN trannie), HP3456 DMM (bad ROM), Radiometer 106 RF Generator
(stuck keys), Genrad 1688 Digital RCL meter (another bad ROM) and a "few"
other assorted goodies...
The Tek 576 is my favorite. This unit was the one of the bunch that failed
early and was shelved. It was dusty, dirty, full of spider webs, and
missing one little knob, but in otherwise perfect shape. I got it for $200.
Guys were offering me $750 for it "as-is" on the way back to the car! To
top it off, two tables down from where I got the 576, someone was selling a
*complete* set of the transistor/diode plug-in fixtures. Score #2!
It was a good day..... I used up all of my allocated "luck" for that year. :^)
The 576's collector supply transformers primary was dead-shorted.
Eventually I was lead to Dean Kidd, who sold me a *brand new* one for $75!
Tek even took the bad transformer back for failure analysis!
The HP frequency counter was the longest fix (~2 months). It's all
jelly-bean TTL logic (some ECL), but no "brains" at all! Board swapping
with a friends unit and some "shotgunning" brought it to back life. The
eventual root failure was a single NPN transistor, in a buffer between two
stages of the main 500MHz counters, whose beta had dropped significantly. I
stuck a 2N2222 in there to check it out, and "there" it remains to this day!
Everything else I have was dead, dying or crippled (er, "functionally
challenged"). I even had to repair my 475A O'scope before I could use it!
(It's a "P-I-T-A" to troubleshoot a scope w/o a scope!)
In the days before 'Weirdstuff Warehouse' stopped being weird and simply became
boring, a lot of the junkus electronicus they sold bore a sticker stating:
This equipment is guaranteed not to work - should you find that it does,
we will be happy to exchange it for something that doesn't.
Treat fleas the same.
(From: Paul Grohe (email@example.com).)
Yep! I bought a lot of "goodies" with that little orange and black sticker!!
I resisted the temptation to take it back if it worked. If it did work, I
broke it, then fixed it, so then I would not feel so "guilty". ;^)
Just want to share my experience on repairing electronic
devices in general. After many (most successful) repairments
I've concluded the following:
Take this advice in mind and I hope you can profit from it.
Repair shops probably will throw a stone towards my head ;-)
The closest I ever came to bench tekking was when I would service electronic
organs at a dealer's warehouse. If I spent all day there I'd normally fix
upwards of 20 instruments and "check out" several others. Normally I just "ran
traps" at churches, auditoriums, schools and homes where I got to five or six
instruments a day.
I dealt with intermittents via a little rubber mallet and a can of cold spray!
And, I learned a couple of things:
It was a great little business until the mid '80s when the Casios and the
Yamahas became popular. Now I mostly repair computers with the occasional
piece of HiFi gear hitting my bench. Like that damned Sony 100-disc CD
player that I can't find parts values for!
-- end V2.23 --
And, How Paul Equipped His Home Lab
(From: Paul Grohe) firstname.lastname@example.org).)
"If it's no longer broke, Quit fixin' it!" - Paul Grohe ;^)
The Genrad was the "hair-puller" (really made me begin to doubt my
troubleshooting skills!). It would continually fail it's self check at the
same step. The failure code indicated a certain section of the analog
section, which I *knew* was okay. There is not much to the analog section
anyways! It is mostly jelly-bean, off-the-shelf 74C series digital logic
sitting around a 6502 uProc. After checking *every* analog part (most
out-of-circuit), and swapping all of the digital chips, I concluded it
*must* be the ROM. It was the only part left that had not been replaced! I
posted for a "brain donor" and got a reply. He had two dead units and
offered to send me the ROM's to compare and read. I took him up on his
offer and copied the ROM, and then transferred it to an EPROM. Voila! The
f#@&!#g thing worked! I chased my tail for weeks! It turns out that a few
bits in the ROM were corrupted, and the error was subtle enough to cause it
to just "trip-up" at that phase of the self-test, even though the hardware
was fine. Arrrgghh!! I sent him his ROM's back, with a little "thank-you",
and eventually helped him revive his two units. This was one of those "fun"
Too Bad About the Good Old Days
(From: Mike Diack (email@example.com).)
Harrie's Notes on Repair
(From: Harrie Gulikers (firstname.lastname@example.org).)
Roger's Comments on Troubleshooting
(From: Roger Pariseau (email@example.com).)
(Let duh buyer beware!)
That's me! Flea Markets/Surplus Stores/Salvation Army/Goodwill/thrift stores/Garage-yard Sales/etc...And there is *lots* of good stuff around this area!
I call it "going' Junkin'".
I arrive at about 5:30 AM, so that requires a combo krypton spotlight/fluorescent lamp flashlight (a $3 Goodwill special :^).
I carry with me the aforementioned 8 cell battery pack, 8 "C" batteries, a bright krypton penlight, one of those all-in-one screwdriver/knife/pliers/scissors/bottle opener contraptions ("fishermans friend"?) and a small pocket DMM. All about 5-7 pounds total. I carry it all in a backpack that I wear "backwards" on my chest (for easy access). During the "lull" (around 9 AM), I go back and "load transfer" to the car.
I got it down to a science!! ;^)
After some lucky "scores", and a few *hundred* hours of troubleshooting, I have a *very* well stocked home lab... :^)
My home lab is graced with a Tek 576 Curve tracer (bad Xfmr), HP 5345 Freq cntr (bad NPN trannie), HP3456 DMM (bad ROM), Radiometer 106 RF Generator (stuck keys), Genrad 1688 Digital RCL meter (another bad ROM) and a "few" other assorted goodies...
The Tek 576 is my favorite. This unit was the one of the bunch that failed early and was shelved. It was dusty, dirty, full of spider webs, and missing one little knob, but in otherwise perfect shape. I got it for $200. Guys were offering me $750 for it "as-is" on the way back to the car! To top it off, two tables down from where I got the 576, someone was selling a *complete* set of the transistor/diode plug-in fixtures. Score #2!
It was a good day..... I used up all of my allocated "luck" for that year. :^)
The 576's collector supply transformers primary was dead-shorted. Eventually I was lead to Dean Kidd, who sold me a *brand new* one for $75! Tek even took the bad transformer back for failure analysis!
The HP frequency counter was the longest fix (~2 months). It's all jelly-bean TTL logic (some ECL), but no "brains" at all! Board swapping with a friends unit and some "shotgunning" brought it to back life. The eventual root failure was a single NPN transistor, in a buffer between two stages of the main 500MHz counters, whose beta had dropped significantly. I stuck a 2N2222 in there to check it out, and "there" it remains to this day!
Everything else I have was dead, dying or crippled (er, "functionally challenged"). I even had to repair my 475A O'scope before I could use it! (It's a "P-I-T-A" to troubleshoot a scope w/o a scope!)
In the days before 'Weirdstuff Warehouse' stopped being weird and simply became boring, a lot of the junkus electronicus they sold bore a sticker stating:
This equipment is guaranteed not to work - should you find that it does, we will be happy to exchange it for something that doesn't.
Treat fleas the same.
(From: Paul Grohe (firstname.lastname@example.org).)
Yep! I bought a lot of "goodies" with that little orange and black sticker!! I resisted the temptation to take it back if it worked. If it did work, I broke it, then fixed it, so then I would not feel so "guilty". ;^)
Just want to share my experience on repairing electronic devices in general. After many (most successful) repairments I've concluded the following:
Take this advice in mind and I hope you can profit from it. Repair shops probably will throw a stone towards my head ;-)
The closest I ever came to bench tekking was when I would service electronic organs at a dealer's warehouse. If I spent all day there I'd normally fix upwards of 20 instruments and "check out" several others. Normally I just "ran traps" at churches, auditoriums, schools and homes where I got to five or six instruments a day.
I dealt with intermittents via a little rubber mallet and a can of cold spray!
And, I learned a couple of things:
It was a great little business until the mid '80s when the Casios and the Yamahas became popular. Now I mostly repair computers with the occasional piece of HiFi gear hitting my bench. Like that damned Sony 100-disc CD player that I can't find parts values for!
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