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Toshiba 42H83

Discussion in 'Electronic Repair' started by Charlie East, Apr 18, 2007.

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  1. Charlie East

    Charlie East Guest

    Anyone have a Toshiba projection set sitting around with a digital converter
    board they can part with? I replaced all the 10 @ 16 surface mount caps on
    this one, Fixed some of the problem but not all, This set was donated to the
    Church if I can get it going,
    Charlie
     
  2. Guest

    Just how familiar are you with PTVs ?

    Before you go looking for an expensive part like that you need to
    verify a few things. Did you replace the STKs ? Where did you get
    them ? Did you check all the return resistors ?

    It helps to identify if the problem is in one of the channels
    exclusively, because if it is the problem is usually in the output
    circuit.

    If you don't have a print, get the datasheet for the STK392-110 and
    troubleshoot it like a regular OP AMP. If they use the non-inverting
    input, the + and - inputs should have nearly the exact same waveform
    on them. If they use the inverting input both should be a flatline at
    0 volts. (the + is grounded anyway)

    If you have a generator put a crosshatch on it and observe closely.
    There are six channels, R, G & B, horizontal and vertical each.

    Analyzing this can be tricky. For example if you have a large error in
    the red horizontal, it will appear to have a red vertical error as
    well, even if it does not. Taking a hypothetical case like this let's
    say the red horizontal is out, on the side of the screen where is is
    overstretched, it will appear to have a vertical pincusion error,
    bowed out. On the side where red is compressed it will be bowed in.
    This is because the pincushion is off, but that is because the beam is
    not where it is supposed to be.

    You'll find people quite reluctant to part with good DCMs, or
    hypermodules. It is imperative to know that is the fault for sure. If
    you could provide a picture of the symptom with a crosshatch patter I
    might be able to analyze it. I do these things all day long. I have a
    nice collection of digital convergence nightmare stories if you like.

    IIRC, Tosibas blank the video when they put up the crosshairs for
    adjustment, so you can't really tell if the outputs are clipping. Need
    a scope for that. However, if the error is in one corner on one color,
    it is likely. That generally indicates a defictive STK. Even if
    they're new, I have seen them bad right out of the bag. It happens
    with the 392-110s, but the 4278s are more notorious for it. They are
    not shorted, but they either can't swing fully to the power supply
    rails, or sometimes the slew rate is too crappy. In either case they
    are not shorted nor completely open, just not good enough.

    I tend to think in terms of the TV having one problem. But nowadays
    you can't count on it. Some people will watch a TV until they can't
    see anything. If they donated it this might well be the case. They
    knew it was screwed up, and then it got screwed up worse. They suspect
    the repair bill will be quite high, and they would be correct.

    At any rate, make absolutely sure that the DCM is the problem, then
    next time I am in the boneyard I'll see if we have a compatible one. I
    don't own the shop so I dunno how much, and unfortunately it will
    probably be untested.

    JURB
     
  3. What is the problem? Are you are talking about the Hyper module? Did you
    check the rest of the SMD caps. I have had these modules with bad caps
    among the 470uF and 1uF caps. Some techs are just changing all of the
    surface mount caps. I just check them and any that are suspect change them.

    Leonard
     
  4. Charlie East

    Charlie East Guest

    The original problem was distorted picture,(zig-zag), I found a web site
    that discribed the same problem.(techlore.com). search 42h83 . The tech said
    change the [email protected] surface mount caps on the hyper module. There was also a
    bulletin from Toshiba that said the same thing. After changing the caps, the
    distortion cleared up.
    Convergence looks good, Still picture looks good, but a moving picture had
    a laging effect, kinda like ghost. The tech said I probably still had
    problems on the hyper module I did check the ESR on the remaining caps on
    the board, didnt find any more bad.
    Charlie
     
  5. I would change the remaining caps on the Hyper module.

    Leonard
     
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