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Convergence Problem

Discussion in 'Electronic Repair' started by Tom, Dec 9, 2004.

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  1. Tom

    Tom Guest

  2. BWL

    BWL Guest

    Probably one or more output resistors are open; usually small value 1 watt...
  3. Tom

    Tom Guest

    BWL stated:
    Hmmm...and those resistors are located where? No problem replacing them,
    just knowing which ones. I am working without schematics or manual.

    I was going to replace capacitors in the area of the STK's as my next step
    since I didn't even consider resistors going bad.

    Thank you,
  4. Art

    Art Guest

    There are numerous resistors in the same physical area as the STK devices.
    Check each one and compare those on one circuit withthose in another. If in
    doubt you may want to have a professional have a go at the tele. Or at least
    buy the service manual or a SAMS Photofact.
  5. Robotron Tom

    Robotron Tom Guest

    Art stated:
    Great idea...I'll start on that tomorrow. Am I going to be able to check
    these resistors in circuit? Do you know if this set is capable of
    generating test patterns? I went into service mode but couldn't get a
    pattern to come on.

    I did find the service manual online for $20, so that is going to happen.

    Robotron Tom *remove nospam to email*
    See the Flashback Arcade at: http://

    Standing for right when it is unpopular is a true test of moral
    -M. Smith
  6. BubbaJim

    BubbaJim Guest

    Will the affected color(s) convergence adjust vertically and
    horizontally? If they do , resistors probably are NOT the problem, you
    could be looking at a bad yoke (only saw it once) or a bad DCU. Pull the
    affected yoke and look for evidence of arcing/burning.
  7. Art

    Art Guest

    Agreed, Bubba: Toshiba has encountered a fair number of defective yokes,
    that can be easily diagnosed by doing a DC resistance or even ringing them.
    The DCU is another possibility but almost as rare as the yokes.
  8. John Del

    John Del Guest

    Subject: Re: Convergence Problem

    I've changed plenty of Toshiba yokes. The ones that show physical damage
    usually cause shutdown, so ringing or scoping the signal is the best option.
    I've also seen bad DCUs and corrupted eeproms in these models.

    John Del
    Wolcott, CT

    "I'm just trying to get into heaven, I'm not running for Jesus!"
    Homer Simpson

    (remove S for email reply)
  9. Tom

    Tom Guest

    BubbaJim stated:
    Yes, I am able to make both adjustments on the blue, which is the problem
    gun. Now, what is a DCU? I haven't heard mention of this acronym yet.

    Thank you,
  10. Tom

    Tom Guest

    Art stated:
    Okay, what the heck is 'ringing'? That is definately a new one on me.

    Thank you,
  11. Robotron Tom

    Robotron Tom Guest

    John Del stated:
    Sorry, I just remembered that after this blue skew came about, sometimes
    the whole picture would do a kind of wide angle jump. It made the picture
    look a bit wider and it would only happen for a few seconds then go back
    to a normal size image. This affected all colors.

    Does that indicate another problem or could it be a part of this problem?

    Thank you,
  12. James Sweet

    James Sweet Guest

    Or just swap the plugs with one of the other yokes and see if the problem
    stays with the same color.
  13. James Sweet

    James Sweet Guest

    Using a flyback "ring tester" essentially injects a signal and counts the
    number of times an inductor resonates. A shorted turn will kill this
    resonation very quickly.

    Should be ok with a DC ohms test though.
  14. Tom

    Tom Guest

    James Sweet stated so wisely:
    HEY...great idea!

    Now...I read somewhere that these projectors don't hold a charge like a
    CRT. Will I need to discharge it before removing??

    Thank you,

    "That man is richest whose pleasures are cheapest."
    -Henry Thoreau
  15. Tom

    Tom Guest

    James Sweet stated so wisely:
    Ahhh...I don't have that kind of equipment, as you've probably guessed.
    And what Ohm range should a good flyback be?

    QUESTION: Is there a chance that this <gun> might be low on fluid?
    I apologize for not knowing the proper term for this component. Could you
    please correct me on the nomenclature?

    I do have a scope(although not very versed on it's usage), is there
    something I could check that will narrow this down quickly with it?

    Thank you,

    "That man is richest whose pleasures are cheapest."
    -Henry Thoreau
  16. James Sweet

    James Sweet Guest

    They're CRT's like any other and can hold a charge, but you're just dealing
    with the yokes, not the HV, don't worry about it. You're more likely to
    shock yourself trying to discharge the CRT's than if you just leave that
    part alone.
  17. Tom

    Tom Guest

    James Sweet stated so wisely: I get it. I misunderstood you the first time. That is a
    simple check. I'll check it and get back here to let you know.

    Thank you,

    "That man is richest whose pleasures are cheapest."
    -Henry Thoreau
  18. James Sweet

    James Sweet Guest

    If you ever start repairing more TV's and stuff you can pick one up for
    under $50, they're pretty simple instruments.

    Flyback? I thought we were talking about yokes? You generally can't test a
    flyback with an ohm meter, good ones are all over the map.
    The CRT could be low on coolant, but that'd be easy to check by just peering
    down the lense with a flashlight, if it's low it should be obvious.
    Not really, a scope is only useful if you know what to expect so you can
    compare it to what you see.
  19. Tom

    Tom Guest

    James Sweet stated so wisely:
    This is a project and money saver for my retired dad, so not likely. :)
    Yes, my mistake.
    Okay, the CRT doesn't appear to be low on coolant. I did look inside
    through the lens with the set on. Knowing that the skew was on the left
    side of the screen, I looked into the lens of the blue CRT and on the
    right side and I could see the skew very well. (It looked as if a sheet
    of clear (or blue) plastic was in there and it had an upward curve in
    that area as if it had been heat warped. I realize there isn't a sheet of
    plastic in there, that's just what it looked like.

    I replace the front screen and tried the user convergence adjustment
    again and the blue + that is usually over the white(red/green/blue) +, is
    way over at the left edge so that I can only see the right tip when I
    move it to the right as far as it will go. I can see that tip move
    up/down/left/right, although if I move it left, the tip disappears.

    So...anymore ideas or information you need to help diagnose this?

    If the CRT is bad, what will a replacement cost me?

    Thank you,

    "That man is richest whose pleasures are cheapest."
    -Henry Thoreau
  20. James Sweet

    James Sweet Guest

    The CRT is fine, it's lighting up, so at any rate it's not the cause of this
    problem. If the yoke is bad, who knows, you might be able to repair it or
    find a good used one. The yoke could be fine though.
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