RCA 21" triage CTC20 CTC16x CTC12

[DavGoodlin]

Some more caps replaced and still the same issue. The 47pf feeding AFC diodes from 6KA8 plate was a suspect along with seven others identified in the "RCA color tv service manual" to which I am referring any schematic notes to. I have an 820pf and 27pf yet to try.

Vertical lock is OK but horizontal is affected by the phantom stuff riding on what should be a cleaned up, semi-sine shaped horz sync pulse. It is no wonder the video pulls and loses lock-in, sometime locking with a blanking bar on the left side.

[JohnCT]

Originally Posted by DavGoodlin

Vertical lock is OK but horizontal is affected by the phantom stuff riding on what should be a cleaned up, semi-sine shaped horz sync pulse. .

Maybe I missed it, but have you tried another source besides the VA48? I have two and both had issues with failing bypass electros in the power supply and on the generator boards.

John

[DavGoodlin]

Originally Posted by JohnCT

Maybe I missed it, but have you tried another source besides the VA48? I have two and both had issues with failing bypass electros in the power supply and on the generator boards.

John

My scope at input (6KA8 pin 6) shows a very noisy video with AC riding it. I assume the noise inverter is meant to clip video, leaving clean sync pulses.

EDIT: Relatively good 6 V p-p video going into 6LF8 pin 2 and then odd stuff at the plate pin 9 at much higher amplitude. The screen grid bypass cap was replaced early on, as it causes these issues in older chassis using a 6AW8.

I will put the VA 48 on a '70 Zenith 16" color and see what its does. It was fine when I was working on a Zenith last month. I have three more orange and maroon drops to try then I give up for now.

EDIT : The Zenith shows a normal picture with fill range of output, and the RCA 16x looks equally un-synced with an air signal .

This is going nowhere, so I change chassis and go back 3 years to a simpler RCA design with a few less "features" in its circuits.

[old_tv_nut]

[QUOTE=DavGoodlin;3229725 ...I assume the noise inverter is meant to clip video, leaving clean sync pulses...[/QUOTE]

The noise inverter is expected to clip noise pulses that go in the direction of sync but are momentarily bigger than sync, like impulse noise from motors. It does not clip video, which is opposite polarity of noise pulses.

[JohnCT]

Originally Posted by DavGoodlin

This is going nowhere, so I change chassis and go back 3 years to a simpler RCA design with a few less "features" in its circuits.

Whatever the problem is, it isn't the design. I worked on many many hundreds of 16s when they were still in daily use (although getting older), and they were always rock solid on any quality of signal.

John

[DavGoodlin]

Originally Posted by JohnCT

Whatever the problem is, it isn't the design. I worked on many many hundreds of 16s when they were still in daily use (although getting older), and they were always rock solid on any quality of signal.

John

Agreed, these look super when something wacky isn't going on. I just need a break but I appreciate the help everyone.