DIYbanter - View Single Post - Sony tech: I need your help! KV36FS320 dead

Ray Carlsen

Good info is worth repeating:

wrote:
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
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