RCA 8TS30 - no picture

[bigaudioal]

I have been fighting with a friend's 8TS30 for a few weeks now. Set was recapped, gets good audio and a raster. But no picture. I have spent the last few weeks restoring a B&K 1075 for injecting signals. Well today was the day to try injecting a signal into this set to see if I could figure out where the video was getting cut off. Figured I'd start injecting at the video output tube and work backwards through the IF stage. Well I didn't even get past the first injection. The raster did darken a bit injecting into the grid of the 6K6, but no real signal. I made sure I was not overdriving the signal from the 1075 into the set. However I did notice that the contrast control/AGC really does not appear to do much when adjusted. I then ohm'ed out the contrast control and it only measured 2k. Shoukd be 10k. Could an AGC issue affect injecting a signal into the video output tube? I know if the AGC is not right it can overload the IF stage. Trying to figure out why I get no signal from the video output tube and after. Or do I need to back-track further to see a signal? Or does this AGC issue just kill all chances of a signal getting through? First time doing this signal injection, so any advice or insight would be greatly appreciated.

I know the B&K is working well. Injected signals into working sets and looking good. See attached photo.

Thanks guys!!!

[Electronic M]

If the video out is tied to the AGC then it can kill the gain there. The IF will definitely be dead if the AGC is off enough.

[Gleb]

Check the negative voltage (-18v) on the contrast control. The video amp gets the bias from that point as well. Significant overvoltage there may completely lock both the IF and the video amp.

[bigaudioal]

Originally Posted by Gleb

Check the negative voltage (-18v) on the contrast control. The video amp gets the bias from that point as well. Significant overvoltage there may completely lock both the IF and the video amp.

Thx. I will check that negative voltage. Plan on replacing the control anyway since it is only measuring 2k when it should be a 10k control.

[Penthode]

I do not believe the 8TS30 employs agc. The gain of the if amplifier is controlled by the contrast control.

[bigaudioal]

Originally Posted by Penthode

I do not believe the 8TS30 employs agc. The gain of the if amplifier is controlled by the contrast control.

Was able to track down a replacement contrast control. Now just have to find time to install it and see if it helps.

[bandersen]

No, you don't need to go further back. I don't believe the contrast or AGC has any effect on the video out.

Did you check the peaking coils for continuity ? Does the brightness control work ?

[bigaudioal]

Originally Posted by bandersen

No, you don't need to go further back. I don't believe the contrast or AGC has any effect on the video out.

Did you check the peaking coils for continuity ? Does the brightness control work ?

I did check all the coils. All have continuity. The brightness control seems to be working fine.

[Kamakiri]

Who knows. I've tried so hard to forget all the damn issues I had with that set