Today's Mystery Guest (RCA CTC-4)

[Phil Nelson]

Thanks, I have tried injecting a video signal (color bars) at the input of the first video amp, without getting a coherent color image. I believe the TV expects a signal of about 2.7 volts there, but my generator can supply only 1.5 volts at most, so perhaps the signal is just too weak.

The RCA manual ( http://antiqueradio.org/art/RCA%20CT...e%20Manual.pdf ) has an interesting section on pages 22-23, "AFC alignment used for chrominance circuit analysis." It explains how to remove the chroma bandpass tube and then measure voltages at the chroma phase detector, R-Y/G-Y demodulators, and 3.58-mc oscillator, to determine whether the 3.58-mc signal is present and traveling where it's supposed to go.

My set flunked all of those tests, so I am starting to wonder if it has more than one problem (wouldn't be the first time). For instance, maybe it has lousy video alignment AND the chroma reference oscillator is not running (or running at the wrong frequency).

I thought I had licked the IF socket problem. I gave all three sockets yet another military-grade cleaning and then resoldered the 3rd IF socket pins. This seemed to eliminate the intermittency, but after messing with various things for a couple of hours, the problem returned.

Tomorrow I'm going to complete the systematic voltage & resistance checks which I started a long time ago and never finished.

Phil Nelson