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PIONEER 1996 model SD5193K?? peculiar problem...

Discussion in 'Electronic Repair' started by Phil Bowser, Jan 19, 2005.

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  1. Phil Bowser

    Phil Bowser Guest

    Today I spent far too much time today trying to diagnose a problem I
    have never seen before (On any proj. TV, for that matter...) I thought
    maybe it was just strange enough that somebody has run into it before...

    Set powers up, displays picture and sound from all inputs. Usually
    when cold (very first turned on) pix is correct on screen, then begins
    shifting to the right (takes about 10 - 30 seconds.) During the transition,
    the picture squiggles a little like a poor AFC lock on an old directview
    zenith. Once the picture is shifted about 3 inches to the right (leaving a
    black blanking bar on the left 3" of the screen) it stabilizes, and will
    play indefinitely in this condition. Convergence is correct, RASTER is
    correct, On Screen display is correct, just the video "slides to the
    right" - if you have the OSD called up while picture is shifting, you can
    see the video sliding the the right, while the OSD remains in its correct
    position. Since the raster and geometry are correct, I have ruled out a
    deflection problem. I 'scoped all B+ supplys from Defl./P/S pc board, and
    they are correct & clean. I soldered any connection that looked cracked on
    the P/S/Defl PCB and convergence, as good preventive maint. and replaced
    several lytics that took excessive heat on P/S/Defl. regardless of the fact
    that they read good for ESR and capacitance. I have also sprayed freeze on
    the system control micro, jungle, and Horiz. osc. resonator - unit does not
    return to normal...

    It looks like there is a phase shift in the video versus the deflection,
    but I haven't been able to tell why, since the flyback pulses are clean,
    etc...This one's got me stumped. Anyone seen this before? Any bulletins on
    this? (I don't get to work on as many Pioneers as other brands...)
  2. Guest

    Does it do this on ALL inputs? Tuner, Video, S-video?
    Obviously the horizontal flyback sync pulse is getting to the system
    control as the OSD is in the correct place.

    It truely sounds like an isolated video signal problem, especially with
    the sync part of the signal. This is why it is important to find out
    if it does this on tuner, video , and s-video inputs.
  3. Phil Bowser

    Phil Bowser Guest

    Update, problem solved... I doubt anyone will see anything similar to
    this, but here is what I found anyway...The Horiz. BLK pulse (Flyback return
    pulse) on this set was found to look more like a sandcastle pulse than what
    the schematic called for, which was a nice clean pulse 5Vp-p... My waveform
    was indeed 5 Vp-p, but had a 1.5v approx. "front and back 'porch'" to it...
    There is a strange circuit that feeds back part of the horiz. DRIVE pulse to
    this stage for scan loss blanking, that was pulling this line low during
    periods of horiz. drive "On" time, and thus creating the only way this
    waveform could be pulled all the way to GND causing the complicated waveform
    I saw there... Defeating this feedback caused the waveform to rise to the
    lowest point of approx. 1.5V (where the tops of the extra porches were
    seen...) I saw no pullup resistors, etc. that should have been able to
    cause this distortion in the waveform, but surmised that this extra rise in
    the waveform in the "undefined state of 1.5Vdc" above GND could be causing
    the jungle to sync off the wrong part of the pulse. Turns out I was right -
    one of the little buffer transistors (2SC27xx) on the "CNR" board was at
    fault - electrically leaky C-B only under was backfeeding a DC
    voltage into the blanking pulse, and was only being pulled to ground during
    on times of horiz. drive from this other feedback circuit. I simply
    disconnected the CNR board to verify correct positioning of the picture,
    then repaired the board by replacing the xistor & reinstalled it to get my
    color back (Color Noise Reduction PC Board is only used on the 5193-K
    model.....) Man, I am glad to see this one resolved!

    Special thanks to Asimov, who seems to have been on the right track, it
    indeed was the blanking pulse getting distorted - in this case, broadened at
    the base...
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