Sony tech: I need your help! KV36FS320 dead

[Ray Carlsen]

This Sony KV36FS320 will not power up, just 9 flashes of the standby/timer LED,
unless I press the power button while energizing the power relay manually, ie
Q608 base drive for 1 second. Then the set will run and -everything- works
until I turn it off again. All standby supplies are working, zero cross pulses
are there, and the M board has been swapped. That's where the power-on pulse is
supposed to originate but there is no pulse at power up. I really need your help
with this one. Thanks in advance! Ray Carlsen, A/V engineering, University of
Washington, Seattle

Ray

 

[Leonard Caillouet]

Possibly Q605, Q606, D690, but resolder these and everything in the ZCD and
standby circuits before replacihng parts.

Leonard

 

[Ray Carlsen]

This Sony KV36FS320 will not power up, just 9 flashes of the standby/timer

Possibly Q605, Q606, D690, but resolder these and everything in the ZCD and
standby circuits before replacing parts.

Leonard,
Thanks for the tips, but I've been over those parts (voltage checks and
resoldering) and can't find anything wrong. I just noticed one other thing,
however. If the set is running and I turn it off with the power switch, the
screen goes to a blue horizontal line before it turns off. If there is a
vertical fault, how does the set run so well when I "kick" start it? How could
such a fault keep the set from even starting up? I keep coming back to the M
board (micro that generates the on pulse) and wonder what might be inhibiting
it. I'm really stuck on this one.

Ray

 

[[email protected]]

Here is a second occurance of the 9 blink ZDC failure. These are not
my words but someone that spent time enough to document this symptom
and post it on Sony's web site.

SYMPTOMS

9 Blinks

RESOLUTION

Z-Det waveform was present, although with no reference, could not tell
if it was correct.
Replaced D640 & D641, then D646, Q690 & Q646, then all the 10k chip
resistors in that circuit. NO improvement.

Checking the Z-Det waveform at the Collector of Q606 found it to be
about .3ms longer than the defective board. In addition to the
slightly longer waveform, some noise pulses that were present on the
waveforms. Replaced Standby Transformer. It did not help. Also tried
D602, no help.

I found the noise was greatest on pin 7 of the Standby Transformer.
Disconnected D647. Noise gone. Replaced (new) D647. Noise is back.
Replaced Q605 and noise was gone and set working again. Apparently,
one of the junctions was flaky at certain voltage levels, causing
noise (change in load) on the collector that was seen back through the
Standby Transformer and was causing the ZCD circuit to malfunction.


Have subsequently found that a bad Q605 can generate the above
mentioned noise pulses. Replacing Q605 cured the problem. A bad D690
could also cause the problem

 

[Ray Carlsen]

Good info is worth repeating:

Here is a second occurance of the 9 blink ZDC failure. These are not my words
but someone that spent time enough to document this symptom and post it on
Sony's web site. SYMPTOMS 9 Blinks RESOLUTION Z-Det waveform was present,
although with no reference, could not tell if it was correct. Replaced D640 &
D641, then D646, Q690 & Q646, then all the 10k chip resistors in that
circuit. NO improvement. Checking the Z-Det waveform at the Collector of Q606
found it to be about .3ms longer than the defective board. In addition to the
slightly longer waveform, some noise pulses that were present on the
waveforms. Replaced Standby Transformer. It did not help. Also tried D602, no
help. I found the noise was greatest on pin 7 of the Standby Transformer.
Disconnected D647. Noise gone. Replaced (new) D647. Noise is back. Replaced
Q605 and noise was gone and set working again. Apparently, one of the
junctions was flaky at certain voltage levels, causing noise (change in load)
on the collector that was seen back through the Standby Transformer and was
causing the ZCD circuit to malfunction. Have subsequently found that a bad
Q605 can generate the above mentioned noise pulses. Replacing Q605 cured the
problem. A bad D690 could also cause the problem

Nipperchipper,
Thanks a lot. You nailed it! The zero cross pulse (pin 15 of the M board to
an input of the micro) showed some horizontal jitter on the scope which I
overlooked before. Swapping Q605 made no difference but diode D647 did. With a
replacement diode, the pulses are stable and the set now comes on normally. A
check of that diode shows a -tiny- bit of reverse leakage on the highest scale
of my old analog meter. Although Sony used a 1 Amp 60ns diode, it appears any
ordinary PS diode will work... I first tried an ECG116 (set worked normally) but
I replaced it with theirs just to be sure. Thanks again!

Ray