Television Salvage

Do NOT! repeat NOT! let the calculus intimidate you. You don't really need it, unless you intend to emulate the likes of Win Hill, Spehro Pefhany, or John Woodgate, inter alia. ;-)

If you can get complex arithmetic (a + bi, which in electronics is a + jb), you're home. All AC is is a vector that's twirling around the origin; resistance is to the right, capacitance is up, and inductance is down. (or maybe vice versa - I never learned it, and have been doing effective electronic circuit-copying for a number of years. ;-) )

Read, read, read.

Did you get any of the projection CRTs? They could be fun.

I'd say, don't start stripping the boards right away - learn as much as you can about what you have on hand - when/if it comes time to strip the boards, you can do it with a propane torch, vise-grips, and safety goggles. ;-)

Cheers! Rich

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Sorry -- not quite what I meant. This works on single sided boards with through hole components. Apply the heat gun to the UNDERSIDE of the board, and carefully pull the components from the top. If you apply a heat gun to the components directly, you'll kill almost all of them. Again, do this in an area that's well ventilated and away from the kids.

Good luck, citizen Chris

Thanks for all the tips.

Good to hear I'm not out of the game on account of my trouble with high math.

I didn't get the CRTs but I got CRT boards . . . . maybe i should go back and grab them? What can I do with them? I know I smashed one, before I realizaed they were easy to unmount.

I just got a desoldering iron and am going to see what's under this IR receiver shielding. I think it's supposed to be jumpered (I separated all the boards so I'm just guessing) to a philips HEF4538BP retrigerrable monostable multivibrator IC. And then to another one. They're like 555s, no? They're on the "Interface Board"

I'm not going to do a whole lot of stripping, if only because it would take me weeks . . .

I have the $70 radio shack DMM and it comes with software/cable for a computer app that apparently can behave like an oscillator. Dunno how good it is. Unfortunately I can't find the CD . . .

Here goes nothing!

how

You've got a pretty good basic meter -- you can directly check diodes, transistors, caps, and resistors. Make sure the caps are discharged before testing.

Possibly you can borrow a meter, copy the software on the CD, and return it.

Good luck Chris

Just found a smashed large-screen rear projection TV near my house. I grabbed all the circuit boards, plus the speakers and what I believe is a remote infrared sensor.

So what's next? Do I desolder everything one a time and put in bins? What's a good thing to get to organize this stuff? Or are some of the circuits going to be useful as is?

Is there a trick to desolder entire circuit boards? I guess not.

My experience/knowledge level is: hardly any. I'm reading a college level electronics text and am discouraged by the calculus needed to understand AC circuits.

Thanks!

One reason for leaving things intact is that you can extract information from the circuitry. So the infrared sensor is coupled with an IC to amplify it, and you'd likely want the whole thing. If you take it apart before you know what you have, you'll have the parts but not how to put them together. OFten it can be easier to trace out the circuit than find information about the IC, or at least how to use the IC.

In the old days, there was little in the way of specific parts, so it made sense to strip away. But even then, it was worth figuring out where the windings on transformers went, so you had a basic idea of function.

Generally, and expecially when starting out, it makes sense to just strip. At that point, you may not be able to make use of specific things, but neither will you have a good stock of supplies. So all those generic parts, resistor, capacitors, diodes and transistors, will build up your stock. Those will work in no matter what you build, and even transistors can often be used if they match the same general specs as those in a schematic.

The fancier circuitry can come later, and you'll have a better idea of what is what. WIth experience, you know what many components are for, and by looking at the board gather lots of information. Like, once you know what an IF filter is, when you spot it you'll be able to tell that the nearby IC is related to it, and you'll know that a key bit of information you need to use that filter is the input and output termination, so you look at the resistors on the input and output. You'll know that an IR detector will always be linked to an amplifier, so you look at both together.

A lot of ICs will not have much use unless you are building, or whatever you are grabbing components from, because they are too specialized. The lower level the IC, the more likely it can be useful. With experience, you can tell what these are, and you'll be able to immediately find the audio amplifier IC, and grab that.

Michael

Got it on the 2nd try.

Is a heat gun different from soldering iron? Otherwise, I'm doing just as you advise . . .

I bought some big alligator clips to heatsink ICs and transistors while removing them.

On another note, I've tested 2 identical electrolytic capacitors and both are reading 0 on my capacitance testor. I've tried reversing leads, though there's no indication on the cap that they're polarized. I succesfully tested a ceramic(?) cap. This TV has has crud all on the boards, had water in the CRTs, and many of the circuit boards were cracked. I'm surprised I didn't find a family of racoons or a bird's nest in there. In other words it's old, so is it possible that all the electrolytic caps are dead? Those are the ones that don't last, right?

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You have to be careful with applying way too much heat to circuit boards. FR-4 starts outgassing at over 300C, and you get hydrogen bromide and oxides of nitrogen -- not too healthy. Maybe it's best to stick with the soldering iron, at least as a newbie.

There's a sea of junked electronics out there, especially if you tell people you'd like to have them give you their old non-working stuff. The item you're working on seems to be in pretty bad shape. It might be time to move on to something else.

Electrolytics will usually be OK with water as long as they haven't been immersed, and there was no exposure to water while the power was on. Just make sure they're dry before you start. Condensation from being outside for an extended period (dew) is another story, though. And condensation combined with freezing can destroy a cap right off.

It can be trivially easy to ruin an electrolytic from overheating when desoldering, especially for a newbie. It might be best to ask someone who knows to show you how to do it and provide a few practical tips.

-- FREE ADVICE WARNING -- By the way, life is long. If the world of science and electronics interests you, not having at least a passing knowledge of basic calculus is like going through life with an eyepatch over one eye and wearing dark sunglasses. Many junior colleges have courses in adult ed which offer calc. Eventually, you should take the time to sharpen your tools and learn the language of the physical world.

Good luck, citizen. Chris

Of course, junked electronics is pretty plentiful. Unless one finds a relatively rare item, say a shortwave receiver which I don't find in the garbage, there will be plenty more to come.

Michael

I wouldn't bother stripping resistors expect for power resistors. Regular 1/4 watt resistors are cheap enough to buy, and they will have full-length leads. Capacitors might be worth it, depending on how much you value your time, but stripped caps will probably have leads too short to get into a proto-board. Note that even if the leads are decent length, the ends have to be really clean of solder in order to get into the proto-board holes. Transistors and other active parts are probably worth it. Don't bother with chips that you can't identify.

One sleazy trick I've used for quick desoldering is to heat up the joint and then WHACK! the board on the bench top. The solder will fly out and leave little splashes on the bench, but they won't do any damage and are usually easy enough to clean up. (Or use an old board on top of the bench.) This not only works better than a solder-sucker, but it's really fast and convenient once you are on a roll. I've heard of some folks who use a torch and desolder whole sections of a board at once like this, but it sounds like it might take a bit of practice...

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Seconded.

Also, if you aren't really interested in the mechanics of mathematics (proofs and such), but you want to understand what's going on, go the the library and check out the first volume of the Feynman lectures, and look at chapter 8 on motion. It basically teaches you differential and integral calculus in a single chapter.

There are a few other chapters for people wanting to learn math. For example, chapter 22 goes through from algebra to complex numbers; chapter 6 goes through probability.

The book is a wonderful resource. The chapters on relativity are classic (so to speak). The sections on color vision, and the mechanisms of seeing are fascinating. He has a chapter on Rachet and Pawl, which goes from simple machines to reversability to entropy.