Stumped with a K7000

Hey guys,
OK, here's the deal...

I have a 19K7901 that I received in non-working order. The previous owner
had capped it, replaced the flyback and HOT. Turns out the HOT was not
insulated, hence no workie. I replaced the HOT, and insulated it, and the
monitor worked fine for a while, with the exception of occasional flickers
(like the HV shutting down momentarily).

Well, it decided it didn't like working here anymore and quit.

I pulled the chassis and started testing it out. The HOT had died again,
and the voltage reg at IC4 appeared to be shorted. I'll skip a bunch of
boring details, but here's where I'm at now:

Pulled IC4, and it is not shorted out of circuit. I ordered some to have on
hand anyway, but I think this one is OK.

If I power the chassis up on my bench, B+ only measures around 18VDC, IIRC.

I have pulled the HOT and IC4 and powered the chassis without them. The pad
for pin 1 of IC4 is still only getting around 24VDC. The left-hand side (on
the schems) of R103 is getting 120-ish, though.

I clipped the blue lead off R301/302 (the right-hand side on the schems),
and powered it up again. Now pin 1 where IC4 should be starts off around
70VDC and slowly trickles up to 120-ish. Powering down, that pin slowly
trickles back down.

On a whim, I replaced C55, C56, and C57, and reconnected the other end of
R301/302. Still only getting about 24VDC at the pad for pin 1 of IC4.

Thoughts?

Thanks,
Rob

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Received on Sat Apr 3 12:15:12 2010