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Television Salvage

Discussion in 'Electronic Basics' started by CitizenRuth, Mar 11, 2005.

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  1. CitizenRuth

    CitizenRuth Guest

    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!
     
  2. 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
     
  3. Chris

    Chris Guest

    Hi, Citizen! You're going at learning about electronics the right way.
    Just taking things apart to see how they work and scrounging
    components is a really good way to pick up a lot of practical
    knowledge.

    You've gotten a lot of good advice from another post. If I could add a
    few things:

    * There is no magic bullet for stripping components off boards.
    You're going about it the right way, one component at a time. If
    you've got a single-sided board or only have components on one side,
    you might want to experiment with heating the solder joints with a heat
    gun to get through hole parts. The circuit board itself may char a
    little and start smoking, so spread the heat around, and do it
    somewhere there's good ventilation. But removing components with a
    soldering iron and a Solda-Pullit suction tool is good practice. Work
    on not overheating components -- you can easily damage them. You might
    want to get a $10 DMM with a diode checker to run basic checks on
    components before you store them.

    * To start out with, just get a few small boxes for components and
    label them "Power Resistors", "Caps", "Diodes", "Transistors", &c. As
    you go on, you can pick up those 60-drawer bins with the molded plastic
    mini-drawers and metal frame at your local hardware store when they're
    on sale.

    * You'll learn a lot more about electronics if you poke around a
    working circuit. You'll get your money's worth if you pick up an old
    AM/FM transistor radio - no ICs - you won't have to worry about
    potentially dangerous high voltages. Take the time to figure out how
    it works with it on.

    * While you're scrounging at garage sales, keep an eye out for a used
    oscilloscope. That single tool (even an old 10 MHz single trace scope)
    will teach you more about electronics than anything else.

    * You've got the wrong textbook. While calculus is necessary to
    really understand AC circuits, that level of knowledge isn't necessary
    to learn a whole lot about the subject. Start out by asking at the
    local trade school or junior college what text they're using for basic
    circuits. These schools teach non-calc based electronics (and they're
    also a good source for used test equipment).

    Good luck, citizen.
    Chris
     
  4. Rich Grise

    Rich Grise Guest

    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
     
  5. Chris

    Chris Guest

    Chris wrote:
    <snip>

    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
     
  6. CitizenRuth

    CitizenRuth Guest

    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!
     
  7. Chris

    Chris Guest

    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
     
  8. CitizenRuth

    CitizenRuth Guest

    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?
     
  9. Rich Grise () writes:

    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
     
  10. JeffM

    JeffM Guest

    capacitance is up, and inductance is down.
    Got it on the 2nd try.
     
  11. Chris

    Chris Guest

    right?

    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 --
    <rant>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.</rant>

    Good luck, citizen.
    Chris
     
  12. Bob Masta

    Bob Masta Guest

    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
    www.daqarta.com
     
  13. 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.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
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