Sony projection No raster, has sound, AP chassis KP-53XBR35

[Mirek Chmiel]

After successfully fixing convergence problem few months ago(by changing
STKs), I'm attempting another repair on this TV.

Few weeks ago it started to sound high pitch noise after warming up for few
hours. After being off completely for a week (we went on vacation), it would
power up with intermittent picture problems. Picture was shaking and I could
hear buzzing noise from one of the components. After checking for various
suggestions on this newsgroup, I looked at board A and resoldered some bad
looking connections. Now the picture wouldn't come up but the noise remained
for a while and then that part of the circuit was shutdown. Then I moved to
the N board and did the same treatment. This time I found a badly broken
solder joint on one of the Df. Bias diodes. I also resoldered few other
places.
Next I checked few places with the scope and compared to the schematic. The
waveforms on that board look OK.
One place, that is way off DC wise is
the collector of the Df. Out transistor (Q853). According to the schematic
it should have 368V. This point is unstable and reads Min. 177, Avg 279 and
Max. 435 V.
Additional info: Audio is OK and can be changed, same with channels.

I'm in the process of checking surrounding components.

Any other ideas?

Thanks,

Mirek

 

[Brett]

After successfully fixing convergence problem few months ago(by changing
STKs), I'm attempting another repair on this TV.

Few weeks ago it started to sound high pitch noise after warming up for few
hours. After being off completely for a week (we went on vacation), it would
power up with intermittent picture problems. Picture was shaking and I could
hear buzzing noise from one of the components. After checking for various
suggestions on this newsgroup, I looked at board A and resoldered some bad
looking connections. Now the picture wouldn't come up but the noise remained
for a while and then that part of the circuit was shutdown. Then I moved to
the N board and did the same treatment. This time I found a badly broken
solder joint on one of the Df. Bias diodes. I also resoldered few other
places.
Next I checked few places with the scope and compared to the schematic. The
waveforms on that board look OK.
One place, that is way off DC wise is
the collector of the Df. Out transistor (Q853). According to the schematic
it should have 368V. This point is unstable and reads Min. 177, Avg 279 and
Max. 435 V.
Additional info: Audio is OK and can be changed, same with channels.

I'm in the process of checking surrounding components.

Any other ideas?

Thanks,

Mirek

which component had the buzzing noise? Try resoldering the pins on the
microprocessor IC. If no luck do the same on the video IC. Problem
sounds like it's in the front end, since both sound and video are
affected.