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Toshiba 50HX70 convergence question

Discussion in 'Electronic Repair' started by Guest, Sep 26, 2005.

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  1. Guest

    Guest Guest

    Hi. I have a 50HX70 Toshiba here. Replaced both convergence STKs, which
    fixed many evils. However, the red is bowed well up at top and well down at
    bottom. Left and right is fine. Tried another new STK for the red vert, does
    the same. All the resistors check good, and I have control of the
    convergence through the menu, but it does not have the range to bring the
    red in line with blue and green. Just need an inch more. Will continue my
    checkings, but wondered if anyone had seen this before. I feel I'm missing
    something simple here.

    Thanks in advance, Danny
  2. Guest

    Guest Guest

    Disregard last. One of the 1.2 ohm resistors was drifting under load.
    Changing them fixed last of problems, in theory.

  3. Markus

    Markus Guest


    This looks exactly what I would have posted, I have one doing the
    exactly the same thing. It first had bad green conv, I mean really
    out on the green, Found one of the 1..8 ohm open, checked all the
    caps around, visually that is... didn't pull any... all looked OK...
    found one of the STK mods shorted, ordered a set of the 1.8 ohm flame
    proofs, all six, cheap enough. Also ordered one of the STK's from MCM,
    problem fixed, so I thought. About a week later customer calls back,
    went out, noticed that one of the 1.8 ohm resistors that I replaced
    was 'toasting out' checked it, it read around 2.2 ohms... so... I
    ordered both STK's figuring, that, perhaps, the mate for the other
    side was toasted as well, "I don't have a schematic for this beast'
    but, followed the traces back, looks like the 3 amps in each module
    cover the three colors in some sort of push pull arrangement. Well,
    after replacing both units the problem still persists. I haven't been
    out yet to check, customer lives a ways out and I really don't want to
    try to lug the entire unit back to my shop, figure to would do more
    damage moving it. I've been just pulling boards and bringing them
    back to my shop. can't really fire them up here at my shop, so, it is
    just go over them with my meters. The one I have will run fine for
    about 5 minutes and then begin to drift out slightly on the red, top
    left side of the screen. I did notice that the STK's run pretty warm.
    I did the convergence from the remote, the one that comes up with the
    1 thru 9 on the screen, set also has a auto focus button, not sure how
    that works with the CPU, might be that we have to put the unit into
    some sort of primary convergence mode. I've heard that there is some
    sort of overlay that goes over the screen and that there is a 'secret'
    command string that you enter into the remote to get it to go into the
    crosshatch pattern. Perhaps this needs to be done to lower the
    quiescent bias currents of these circuits. I feel that perhaps it is
    just in need of better alignment. I've seen convergence ckts in some
    commercial cameras that would do the same sort of thing, run really
    hot if not aligned properly, this really goes back when they had
    literally dozens of control pots to do the alignment. Do you know how
    to get this into the secret service mode?
    Why am I replying at 4 in the morning, just had jaw surgery and
    couldn't sleep... one good thing, no cancer,

    Take care,


    of 1.8 ohm resistors and On Mon, 26 Sep 2005 11:48:32 -0500,
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