Nadir:
Sounds to me like basic power supply B+ regulation has failed..... bad
regulator chip, high esr electrolytics, shorted diodes, etc...... a common
high failure part is the STK regulator but the other parts of the circuit
must be tested. Put a meter on the regulated B+ rail and then vary the AC
input voltage with a variac +/- 10 volts to see if the B+ holds steady.
If the problem is not there, then look for faulty screen filtering caps ....
usually low up/high voltage units near and around the flyback...... i.e.
22@250, etc.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-------------------------------------------



"Nadir" wrote in message
om...
I am currently working on an RCA 27" model F27634ET, chassis CTC187BJ.
The original problem was the set would squeal when plugged in and
wouldn't power on. Q401 was shorted B-E, I don't have a BUH517 on
hand so I subbed with a BU2520DF. C4709 was also replaced and I
resoldered the flyback, STK regulator, H-Out transformer and pretty
much most of the deflection/PS section of the board. The set now runs
and the HOT is warm to the touch but well below maximum temperature.
However the picutre changes size dramatically with any change in
brightness. If I turn the brightness down low the picture will shrink
down by about 20% on all sides and there is some pincushion
distortion. I suspected it may be the usual tuner solder problem but
if i bring up a static picture and firmly tap the tuner the picture
doesn't flinch. Pincushion problems are usually related to Q851,
D851, C4803, C4402, C4403, CR4402, C4407 and CR4403 but here they all
test OK. I suspect it may be the STK regulator module failing but I
want to be sure before replacing it. Any help is appreciated.
Thanks.