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Sears TV Vertical Collapse

Discussion in 'Electronic Repair' started by Craig McLean, Apr 14, 2004.

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  1. Craig McLean

    Craig McLean Guest

    Hello I have a Sears TV which currently has vertical collapse (the white
    line across the middle of the screen). The TV is a rebadged JVC of unkown
    model number. The Sears model is 509.14359.

    No schematic is available, however I did some tracing and found the vertical
    section. I poked around and didn't notice any damaged passive components so
    I took a chance and replaced the vertical output amplifier chip (PN:
    LA7832). After I replaced the chip the problem changed, now when I turn the
    TV on it turns itself off after about 4 or 5 seconds. I do get audio, but I
    can't tell if there is any video because the tube doesn't warm up enough for
    me to see. Can anybody give me any hints on what I might have done. I seem
    to have changed the problem.

    Some things I have already tried. I took out the new LA7832 and put the old
    one back in, same problem, TV turns itself off after about 4 seconds. I
    also took a close look to make sure I hadn't messed up the soldering I did,
    but I don't see anything.

    Anybody have any ideas?
     
  2. Art

    Art Guest

    Check the electrolytic caps in both the power supply and in the vertical
    deflection circuit. Also open resistors and damaged traces.
     
  3. Look for a D422 or D442 in that circuit.....should be a 75V Zener. Change
    it.

    Also look for a D542 Shorted Rgp10j = Ecg552 Equiv.

    Also..........check the input/output voltages of any of the 78xx and 79xx
    series regulators.


    --
    ==========================
    Jeff Stielau
    Shoreline Electronics Repair
    344 East Main Street
    Clinton,CT 06413
    860-399-1861
    860-664-3535 (fax)

    ========================
    "If you push something hard enough it will fall over."
    Fudd's First Law of Opposition - Sir Sidney Fudd
     
  4. Craig McLean

    Craig McLean Guest

    First of all, thank you all for your advice. Both the people who emailed me
    and the people who replied here. I found a burned out resistor. Replacing
    that fixed the problem where the TV would shut itself off 5 seconds after
    turning it on.

    Unfortunately after I did that the la7632 chip started smoking and burned
    itself out. Does anybody have any ideas on that? I don't think it is a
    defective component because I tested almost every component in the vicinity
    of the la7832 and they were all fine (with the exception of the resistor I
    mentioned above). The only thing I can think of is I didn't screw the
    la7832 back onto its heat sink before starting the TV up, is it actually
    possible for that thing to get hot enough that fast to start smoking? The
    only thing I can think of is trace damage.
     
  5. sofie

    sofie Guest

    Craig McLean:
    As you have just found out, without being properly attached to a heat sink,
    most power semiconductors operating within normal specification will
    overheat and become faulty almost immediately.
     
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