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Discussion in 'Electronic Repair' started by James Sweet, Apr 9, 2007.

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  1. James Sweet

    James Sweet Guest


    Yes, the diode is probably shorted, chances are that was there in the
    first place to protect against what you did as well as overvoltage. It
    likely was the only problem.
     
  2. Crow Berry

    Crow Berry Guest

    Good Day,

    I accidently wrecked my amplified speakers by reversing the polarity
    from the battery. It is a fairly inexpensive set from radio shack
    with a sub woofer and two small "towers" . I still get a very quiet
    sound reproduction as well as a buzz from the speakers, but nothing
    from the sub woofer. I took it apart and it has a small circuit
    board with a bunch of capacitors, etc on it as well as two amplifier
    IC's. I read about someone fixing something like this by replacing
    the amplifier chip so I replaced them both........a learning
    experience. Anyhow, it made no difference. Now I noticed there is a
    zener diode in the circuit right where the power comes in. Could
    this get fried by giving it the opposite polarity? Any suggestions as
    to how to troubleshoot this would be greatly appreciated. I have
    already invested more time than the darn thing is worth, but I still
    want to try to repair it.
    Brett
     
  3. First you need a circuit diagram.
     
  4. James Sweet

    James Sweet Guest


    Why? I almost never have them for things I repair.
     

  5. Homer works on HVAC.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  6. Guest

    no way do you need a cct diag to fix a blown zener. Nor indeed for a
    large proportion of repairs.


    NT
     
  7. But you have to take into context the original poster and the question.

    I read it to mean someone who isn't regularly repairing things, may
    not even have much knowledge of electronics. And that at the very least
    may require a schematic, if for no other reason than hand-holding.

    Think of when you were young and first looked at circuit boards. How
    much of it was immdiately obvious?

    Michael
     
  8. Eeyore

    Eeyore Guest

    Circuit boards ?

    Graham
     
  9. Now that is funny.

    To be fair, I was thinking in terms of a beginner looking at circuit
    boards today (since they aren't likely to come across something else).

    Nevertheless, it would apply to point to point wiring between tube
    sockets, though those had the slight advantage of being easier to
    trace.

    Michael
     
  10. James Sweet

    James Sweet Guest


    So do I, and the same applies. Those are even simpler electrically,
    practically every system contains the same basic components wired in the
    same way.
     
  11. I assume you have experience. You need one or the other and I doubt the OP
    has the experience.
     
  12. That doesn't help a beginner. After 50 years you can figure out how 90% of
    things work. With 0 years you can figure out how 0% of things work.
     

  13. Homer hangs around ABSE and other electronics news groups pretending
    that he knows something, but so far has never given anyone any useful
    answers. Then he brags that he can't be fired because he's a union HVAC
    man. he would need a schematic, because its out of his field.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     

  14. Yes, but they had tubes on them. Nasty heat damage to those early
    phenolic PC boards by the heat conducted through the pins of the tube
    sockets, too.


    A little snip from: <http://www.americancircuits.com/circuit-board/>

    We, at American Circuits, are here to fulfill all your printed circuit
    board needs. Printed circuit boards were invented in the mid-1930's but
    it wasn't until the 1950's, when the auto-assembly process was developed
    by the U.S. Army, that printed circuit boards have been a part of
    consumer electronics. You can't even begin to imagine how our lives
    would be different without the convenience of printed circuit boards,
    and printed circuit design has progressed to the point that it makes
    them far different than their predecessors.




    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  15. Guest

    A cct diag wont help the OP find the zener, and wont help them replace
    it. Its not relevant here.

    I remember trying to figure out where the voltage dropped :) Had me
    puzzled for ages that did, meters weren't given to kids like they are
    today.

    But understanding the workings of the amp is not something the OP need
    get into. Anyway modern IC amps really dont explain themselves with
    cct diags, theyre just spider structures, a central blob with various
    support components hooked on, all of which do things that are well
    beyond the absolute beginner.


    NT
     
  16. It's highly unlikely there is a zener. Usually there's just a series diode.
     
  17. DaveM

    DaveM Guest

    That is, indeed, a 4.7V Zener diode. Power rating is a guess, but probably in
    the neighborhood of 0.5 to 1 watt.
    To test a zener, you need a power supply that can supply more voltage than the
    zener voltage, at about 10 to 50 ma (DC of course).
    Connect a voltmeter directly across the zener.
    Connect a 1K resistor between the power supply positive output lead and the
    zener cathode.
    Connect the power supply negative to the zener anode.
    Turn the power supply on and slowly turn the voltage control up. If the
    voltmeter reads zero or less than a volt, reverse the zener connections.
    If the voltmeter reads in accordance with the power supply's output as it is
    adjusted, continue adjusting the power supply voltage upwards until the
    voltmeter reads a constant voltage. That reading is the zener voltage.
    If the zener is shorted, the voltmeter will read zero or a very low voltage
    regardless of the direction in which it is connected.
    If it is open, the voltmeter will never stabilize on reading, meaning that the
    zener isn't regulating. Of course, this will also happen if the power supply
    voltage isn't high enough to make the zener conduct. In that case, get a power
    supply capable of higher voltage output.

    Cheers!!!
    --
    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
    address)

    Life is like a roll of toilet paper; the closer to the end, the faster it goes.
     
  18. Meat Plow

    Meat Plow Guest

    http://www.datasheetcatalog.com/datasheets_pdf/B/Z/X/5/BZX55-C4V7.shtmlLook

    --
    #1 Offishul Ruiner of Usenet, March 2007
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    Pierre Salinger Memorial Hook, Line & Sinker, June 2004
    COOSN-266-06-25794
     
  19. Meat Plow

    Meat Plow Guest

    C4V7 = 4.7 volts @ 500 milliwatts


    --
    #1 Offishul Ruiner of Usenet, March 2007
    #1 Usenet Asshole, March 2007
    #1 Bartlo Pset, March 13-24 2007
    #10 Most hated Usenetizen of all time
    Pierre Salinger Memorial Hook, Line & Sinker, June 2004
    COOSN-266-06-25794
     
  20. Crow Berry

    Crow Berry Guest

    O.K. Thanx for all the responses. The circuit board has a label
    " Z 1" where this small glass cylinder is and under it is what looks
    like a symbol for a zener diode. Now I am wondering two things - how
    do you test a zener diode and how can you tell what value it is for
    replacement. The board also has " 4V7" next to the diode symbol and
    with a magnifier I can see " C4V7" and "CH" on the diode itself.
    Also the glass cylinder sort of looks cracked, but it is hard to tell.
    Thanx again, Brett
     
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