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Hitachi part-HC-3041 AP43 chassis

Discussion in 'Electronic Repair' started by [email protected], Sep 10, 2005.

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  1. Guest

    Already changed all the caps, picture has elevated pedestal
    (brightness) and won't sync. The amplitude at the YSY output is very
    low in amplitude, and the set syncs once in a while on a bright scene.
    There is also some horizontal bending, and during a blackout between
    scenes it actuall loses H sync as well.

    I spied the pattern for the plug for a two line comb filter so I
    decided to put one in from "stock". There was no sync at all, I found
    the YSY terminal is not used in a two line equipped set, so I took a
    10uF cap and coupled the Y output to it, and then I got clean Hsync,
    but seemingly no V sync at all. Yall know the architecture of the video
    circuit has become a rat's nest, with the two line filter installed
    there was no sync from the SVHS input either ! This even though with
    the original there was.

    When using SVHS the elevated pedestal is also gone. Picture perfect
    (except for a minor lack of NS pin correction). Trying to think the set
    only has one problem, I unplugged the covergence WF board and it didn't
    clear up the sync problem. Also video response is good, there are no
    trailing negatives typical of video distorted by bad caps.

    The set also KNOWS when it has sync, with no sync the OSD goes into
    default values and is centered, when it has active video (rolling) the
    OSD is shifted up, like it used to in sets without a default no signal
    sync.

    If you got any ideas, great, but I'm starting to think it's time to
    replace the comb filter.

    Anything is appreciated, and I'll buy one from you if you got one for
    sale.

    Thanks in advance.

    JURB
     
  2. Guest

    What caps did you change?
    All the ones inside the comb filter and the pip module?
     
  3. Guest

    I didn't do the PIP module because in an AP43 main video doesn't go
    through it. I've unplugged them with no ill effects, even the PIP
    window comes up, without child video of course. (actually IIRC the PIP
    worked fine on this set)

    Anyway I did change ALL the lytics in the comb filter, first the ones
    that checked bad and all of the same value. When the problem persisted
    I thought maybe one was leaky (brightness too high seemed to be in line
    with that reasoning, maybe), still no good.

    I finally got a 2 line comb filter to work. You have to couple the
    video from the input to the "YSY" terminal. I used a 10uF cap. Not a
    perfect solution, but it was a solution.

    Another very interesting thing about this job is that at turn on, the
    set has a small white dot slightly below and to the right of the center
    of the screen. It goes away as soon as you use any function that
    invokes an OSD. It has to be the micro, but I can't hold up the job.

    I also had to fix the convergence board, had a crack in it, I replaced
    it with one from the boneyard because,,,,, I could. The AP 43 has a
    pretty good control set and even full blown convergence only takes me
    about 20 minutes, if that.

    One thing almost tripped me up, but I was already hip to it, I slide
    the chassis in and reconnect the speakers etc., then turn it on. (I had
    checked the video input/switching board caps because of the symptom.
    I'm sure something on there could possibly cause my original symptom).
    I got it in an fired the set up and had interference lines in the
    video. Then I realized I hadn't yet strapped up the wires. This was a
    case where convergence was deflecting with noise from the SMPS. I
    initially thought it was in the video, but moving the convergence
    output lines away from the SMPS cured it.

    Let that be a word to the wise, when you have a really elusive video
    interference problem on an RPTV, take a minute and disable the
    convergence. I've had this appear to be a video problem more the once,
    the first was an NAP PTV 5 or 600, the last one without digital
    comvergence. The PLL of the WF generator chip was not in sync. I've
    also seen it on a Zenith (9-1674 based chassis), but this Hitachi
    wasn't a hard failure, it was lead dress.

    JURB
     
  4. Guest

    I am curious as it has been years since we had the last one of those
    in.
    Were the capacitors in the comb filter non-polarized ones?
    I seem to remember a similar problem when a tech put polarized
    capacitors in one where non-polar ones should have been used. But I
    cannot remember if it was the Hitachi RPTV set or not.
     
  5. Guest

    I believe there were three, all 10/16. I did replace them with regular
    lytics, but 50 volt units. I have done this before, as long as you use
    a high enough rated cap you can get away with it.

    Let's face it, the whole thing runs on 9 volts, and if they're using an
    np cap there, that means they expect the polarity of the applied
    voltage to change. It's also a good bet that it's a signal coupling cap
    and not likely to see even the whole 9 volts.

    A 10/50 can easily take 3 volts reverse. If some tech caused a problem
    it was probably a cap with a low voltage rating.

    You didn't say that you do, but you, or your organisation should not
    summarily condemn RPTVs based only on age. There are some units that
    have held up quite well. More on this in another thread, I'll start it
    later.

    JURB
     
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