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NO GUARANTEES! DO AT YOUR OWN RISK!This page describes activities which can be hazardous, and which have many things which are totally outside my control. Don't blame me for your problems! You assume all risks if you partake in this activity.
In the June, 2013 issue of Nuts And Volts magazine, someone submitted a question to the "Reader-to-Reader TechForum" on salvaging parts from old electronics equipment. Paraaphrasing what the poster asked: whether it's generally worthwhile, what kinds of old equipment contains the most rewarding, and whether there are parts that deteriorate. Although I've submitted a response, I have a lot more to say than I could reasonably put into that media, so I put this together.
The short answer: Ripping into old equipment that was destined for for the landfill can be fun, educational, and, sometimes, yield some potentially useful parts. There are even aspects of it that many wouldn't think of who haven't done it. However, you also need to be aware that there are hazards, but being aware of them, and how to avoid them, can keep you safe.
Of course, before tearing into a just obtained piece of "junked" equipment, I trust you know enough to make absolutely sure it's not plugged in, and you'll remove any batteries before going any further.
Besides this, any device which has (or should I say, "had") high voltages inside needs to be treated with respect, especially if you don't have a lot of experience. Equipment such as old televisions or computer monitors that have CRTs (picture tubes) can have several thousand volts while operating. Some components can store potentially dangerous voltages for very long times.
But there is some good news: it's easy, and cheap, to make sure any such high voltages are discharged. Here's how:
One lead of the resistor can serve as the metal probe at the end of your chicken stick, though if you use it a lot, you might eventually want to substitute something a bit more substantial. By the way, "pointy" is a good thing for this probe, though I won't go into the physics as to why it is.
Once you've soldered the wire to the resistor, attach the resistor to the rod so that the probe sticks out beyond the end of the rod. Make sure it's firmly attached, using either a zip tie or some electrical tape. Then attach the wire near the resistor, say an inch or so (2 or 3cm) away from the resistor, to the rod, again making sure the attachment is strong. Once you've soldered the aligator clip to the loose end of the wire, your chicken stick is complete.
Once you have your chicken stick connected to something metalic, hold it by the end that's away from the probe end, and use it to touch each terminal of every component in the circuit. You can use the rule of thumb that if it's a big part, hold the probe on its terminals for several seconds. If the circuit is known to have high voltage, make it more than just a few seconds. If yoou're a beginner, and aren't familiar with a lot of electronics, go over the circuit several times to make sure you've touched every pin several times. Then go have a cup of coffee, or some similar other activity for at least a few minutes, then go over the circuit again with the chicken stick. (The reason why is that some types of capacitors can, in essence, regenerate a voltage over a few minutes.)
As I mentioned, every piece of equipment is different, but your first challenge is to get inside (after you've confirmed it is NOT plugged in). Look it over thoroughly. If there are screws, you're probably in luck. You have a fairly good chance of simply unscrewing them and getting into the case. Remember "righty tighty, lefty loosey". If you've taken out all the screws you can find and the case doesn't come apart, rub your thumb nail over any labels – a favorite trick is to hide a key screw under a label. And if that doesn't help, take off any rubber feet, as often screws are hidden under them. If it's a plastic case, look for small inserts that hide screws. Sometimes plastic cases are snapped together. If all else fails, go ahead and apply force and destroy the case, but it's best to try to salvage the case if possible.
I suggest that you also practice identifying what each component on the circuit board is. I've been doing electronics both as a hobbyist and as a professional for over 45 years, and I still get stumped by some parts I see on boards, so don't feel bad if you don't know what everything is.
After you've identified some of the parts, or can make a guess about what some parts are, it might be worth looking at some of the online catalogs to find similar parts. (See my Sources for Parts & Supplies section for some links.) This will help you get an idea of whether or not something is worth salvaging.
There's another thing that you can do with some salvaged printed circuit boards that you might not think of: Practice getting components off the printed circuit board without damaging the board. Although the boards in question are of virtually no value, this is a skill that will eventually come in handy. Eventually when you're doing electronics you'll need to change out one or more parts that are soldered to circuit boards, whether you're trying to get a board of your own design to work, troubleshoot a board you've just built from a kit, or are trying to fix your friend's failed gadget. It is very easy to destroy a printed circuit board when trying to get a part off — so it's much better to practice (a lot!) on boards that are already scrap.
There are lots of different parts that you may run into in a particular piece of salvaged equipment. Here's a partial list that you might run into with some comments on each, in no particular order:
Be aware that if the piece of equipment is particularly old, or has been exposed to high temperatures or other adverse conditions, the insulation may have deteriorated. Inspect it carefully.
Most knobs will just pull off, others will require a small screwdriver or hex key to loosen a set screw.
Sometimes you'll also find linear pots (i.e., "slide controls"). These can frequently be worth salvaging.
But grab the fuse, either way. Use your ohm meter to check ot see if it's blown, and if not, stick it in your "junk box" as it may save a trip to the store to buy one sometime.
At one time, carbon composition resistors were the most common type. However, many folks call them "carbon decomposition" resistors, as even if they've just lain in a drawer for 15 years or so, they'll be well outside marked tollerances. More modern types of resistors are more stable, and I'd expect a wire-wound resistor from before World War II to still be in tollerance.
Be aware that electrolytic caps can deteriorate with age. Most other types of capacitors are fairly stable.
Be very careful extracting capacitors, as there are effects that a capacitor can sometimes "recover" a charge on its own. If it's a 5 volt cap, it's not soemthing to worry about, but if it's a couple thousand volts, be careful.
Old TVs (ones with picture tubes) usually have something called a flyback transformer. This device generated the high voltage to operate the picture tube, usually several thousand volts. They do not connect directly to the AC line — they usually are driven by the roughly 15kHz of the horizontal sweep, with the very steep flyback portion of that signal actually generating the high voltage. Thus the name flyback transformer. These are always in high voltage circuits, so unless you know what you're doing, REALLY know what you're doing, they're best left alone.
Many older circuits, such as radios, have several small transformers. These include small audio transformers, radio frequency or RF transformers, and intermediate frequency or IF transformers. They can be critical to older circuit designs, but aren't used often in more modern circuits.
If you do salvage a tube type piece of equipment, be aware that tubes require a minimum of about 80 volts to function, and many tubes require a lot more than that. So be generous with using the chicken stick!
Pull all of the tubes out of their sockets (although you may not be interested in using them yourself, collectors will want them), and be sure to salvage the sockets, too.
Some things, like old VCRs, have a lot of interesting mechanical tidbits.
If you find a rectangular metal case, be sure to keep it. You can alwas replace the front panel with something. A piece of sheet metal, or a piece of flat plastic, or thin plywood, can give you new front (and sometimes back) panels at a lot less cost than a brand new case.
If you do happen to strip all the parts off a PC board, you might be able to use it in the future as a work surface for soldering.
On the other hand, there are a couple of radio connectors that I happen to have the special tools to get the pins out of them that I will always take, but those are rare.
That said, when you're first starting out, if you find small transistors that are clearly marked as to their part number, and have fairly long leads, you can grab them to play with. If you "let the smoke out" of something you got for free, who cares?
Transistors usually don't deteriorate much with age, though they are susceptible to heat damage as well as both electrostatic damage and damage from overloads.
Even if a speaker doesn't work, it can often yield a magnet that can be interesting, as well as some incredibly thin magnet wire.
Once you've stripped all the parts you want, the best thing to do with the leftovers is to try to get them into the hands of an organization that will recycle them. Most electronics contain small amounts of gold, and even with today's gold prices, it's probably less than a dollar's worth. However, when crushed, old electronics have a significantly higher concentration of gold than most ores that come out of the ground. And there are other elements that can be recovered, such as tantalum and neodymium, as well as others. And, to boot, you may keep some lead out of the landfill. They probably won't pay you anything, but hopefully they won't charge you for accepting it.
In summary, enjoy ripping apart salvaged equipment. You may
find some useful parts, but you'll almost certainly find some
useful knowledge, as some pieces ofequipment provide examples
of excellent design and construction, and others will provide
examples at the other end of the spectrum.
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