RCA 8-PT-7034 issues

[miniman82]

How's the fly ring out, good? It's an autoformer style fly so presumably if there were turns shorted in exactly the right place, you could wind up with high voltage pulses in all sorts of strange places. Ohm out each section, see if the values make sense. Terminals 1/2/3/damper cathode I would expect to be a relatively low value and pretty close in number to each other (perhaps 8-20 or so ohms), and obviously the HV overwind going to the 1V2 will have a higher number to the damper cathode than the others.

Another possibility is that since this is a low B+ chassis, there could be an issue with boost voltage. Anything connected to terminal #1 on the fly has B+boost voltage, so if boost is abnormally high things could start melting in a hurry. Out of curiosity, what voltage rating did C171 have? I see 440v at the plate of the vert output tube, so that cap better have been rated at least 500 working volts/550 surge to be on the safe side.

Incidentally if the VOT blew it's primary and the cause wasn't a ton of boost voltage frying it, the only other reason that would make sense is C153 being shorted to ground.

*EDIT* missed C156, so C153 being shorted wouldn't do much of anything.

[bigaudioal]

Originally Posted by miniman82

How's the fly ring out, good? It's an autoformer style fly so presumably if there were turns shorted in exactly the right place, you could wind up with high voltage pulses in all sorts of strange places. Ohm out each section, see if the values make sense. Terminals 1/2/3/damper cathode I would expect to be a relatively low value and pretty close in number to each other (perhaps 8-20 or so ohms), and obviously the HV overwind going to the 1V2 will have a higher number to the damper cathode than the others.

Another possibility is that since this is a low B+ chassis, there could be an issue with boost voltage. Anything connected to terminal #1 on the fly has B+boost voltage, so if boost is abnormally high things could start melting in a hurry. Out of curiosity, what voltage rating did C171 have? I see 440v at the plate of the vert output tube, so that cap better have been rated at least 500 working volts/550 surge to be on the safe side.

Incidentally if the VOT blew it's primary and the cause wasn't a ton of boost voltage frying it, the only other reason that would make sense is C153 being shorted to ground.

I did ohm the sections of he fly and they all seemed good. C171 was rated at 450. That's what I installed. Schematics also call for a 450 volt cap. Isn't C153 connected to ground?

Thanks for these tips too!!!