PIONEER 1996 model SD5193K?? peculiar problem...

[Phil Bowser]

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...)

 

[[email protected]]

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.

 

[Phil Bowser]

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 voltage...it 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...