Today's Mystery Guest (RCA CTC-4)

[Phil Nelson]

Thanks, I replaced the horizontal output tube right after I fixed the horiz oscillator.

Earlier today I started scoping things in the chroma circuits. Since it's doubtful whether the IF section is passing a color signal, I disconnected the output from the video detector and injected a video signal from the pattern generator at the video amp grid. With luck, I can get some clue whether the chroma circuits are operating.

The waveforms on the burst keyer tube look pretty normal. Here's the burst keyer grid (pin 9):



Here's the burst keyer plate (pin 1):



Here's the burst keyer cathode (pin 8):





I also scoped the bandpass amplifier, demodulator driver, color killer, blanking amp, and G-Y/R-Y demodulator:

http://antiqueradio.org/art/temp/RCA...ndpassGrid.jpg
http://antiqueradio.org/art/temp/RCA...DriverGrid.jpg
http://antiqueradio.org/art/temp/RCA...KillerGrid.jpg
http://antiqueradio.org/art/temp/RCA...ingAmpGrid.jpg
http://antiqueradio.org/art/temp/RCA...ulatorGrid.jpg
http://antiqueradio.org/art/temp/RCA...atorOutput.jpg
http://antiqueradio.org/art/temp/RCA...ulatorGrid.jpg

I haven't pored over all this yet, but I get the idea that some of those circuits are operating, anyhow.

Phil Nelson

[old_coot88]

Phil,
Although I'm not overly familiar with sets earller than CTC-12, I'm assuming the following 'quick & dirty' check is valid for your CTC-4 as well:
While watching the colorbar display as shown in your post# 138, rotate the color control thru its full range, from zero to maximum, a few times. Does that greenish component vary in intensity, extinguishing completely at the zero setting? If so, it indicates the chroma signal amplitude is being displayed, but without the local phase reference signal. In other words, the 3.58 oscillator is not running.