Today's Mystery Guest (RCA CTC-4)

[Username1]

I would check or replace C202,
Check or temp remove C209 - check for grid voltage change.
What resistance grid to ground...?
Check or replace C213.

In that little test, no color barbar-pole means no osc.
No -10v osc not running.

You probably have more than one problem looking at the low signal
quality of the burst way back many posts....

.

[Phil Nelson]

Replaced C202, C209, C213 -- no change. I even swapped 6AZ8 tubes out of superstition, but no go.

I know the video IF section is not great, so I disconnected that and injected video at the 1st video amp grid. Presumably that is a nice clean signal, although maybe not quite as strong as needed.

Phil Nelson

[Penthode]

Originally Posted by Phil Nelson

Replaced C202, C209, C213 -- no change. I even swapped 6AZ8 tubes out of superstition, but no go.

I know the video IF section is not great, so I disconnected that and injected video at the 1st video amp grid. Presumably that is a nice clean signal, although maybe not quite as strong as needed.

Phil Nelson

Are you sure that you have adjusted the fine tuning so that the video carrier is on the correct side of the if response? The consumer rf modulators are double side and the chromance could be lost if mistuned.

Does that make sense?

Terry

[Phil Nelson]

Yes, that makes sense. The tuner is not an issue right now, since I have disconnected the video IF section (and upstream of that, the tuner) to inject a video signal directly at the 1st video amplifier.

When I had things connected normally, I could observe differences when using the fine tuner to tune on either side of the "best" signal, but the TV never displayed anything resembling correct colors. I have done this with various sources -- DVD player, agile modulator, pattern generator, etc. The AGC and color killer appear to be working normally, too.

Phil Nelson

[old_coot88]

Getting the 3.58 osc running should be the #1 objective, irrespective of whatever other gremlins may still be lurking.

[Phil Nelson]

I'm open to suggestions about how to get that oscillator working. There aren't a lot of other components connected to that tube, other than a couple of ceramic caps and a few resistors.

Phil Nelson

[Pete Deksnis]

Originally Posted by Phil Nelson

I'm open to suggestions about how to get that oscillator working. There aren't a lot of other components connected to that tube, other than a couple of ceramic caps and a few resistors.

Phil Nelson

Phil, I'm also fighting a chroma-AFC problem in a friend's CT-100. It exhibits a similar off-color operation. In my case the oscillator is functional and the CW to the demodulators is there and at the proper amplitude. And, as well as can be seen on a scope, the CW is in quadrature at the demodulators.

As has been suggested here with your problem, I will next concentrate on insuring the Reactance inductor and circuit are working properly.

Closed loops are tough cookies to crack at times!

Pete