Fascinating, it's the pre-silicon equivalent of SCR latch-up *grin*
Good news, we have video! Problem was "dumb user". Sometimes my cable box gets in a state where it will output sound but no video (while off). So when I powered the set and got audio, I foolishly assumed the box was on. Actually turning on the cable box got me a picture. It's watchably bright with the controls low, so it looks like the picture tube is in pretty good shape.
Spent some time poking and prodding. Had to adjust the horizontal drive waveform, probably because there was a cap right across the relevant coil that got swapped (all the ones that came out of the set were well out of spec).
A couple of issues observed that I will need to dig into. Some input here would be helpful, but if not I will start from square one since I have three different service guides with all the voltages and waveforms.
1. Looks like bad HV regulation, or low HV. Turning up the contrast or brightness controls makes the picture bloom and lose focus. It fades if you go further, and comes back if you turn it down. The focus control is also at the extreme end of its rotation.
I surmise this may have something to do with the non-connected doorknob cap?
2. Possibly related, picture takes an appreciable amount of time to come up, and does so very slowly. (A good 1-2 minutes. My previous tube set would have a picture not long after you heard the HV come up)
3. Observed that the width coil does not seem to have an effect when adjusted. I'll check if it's gone open.
4. I was setting up the horizontal oscillator per P 18 of the SAMs. There were times where I got to a point that something would go funny when adjusting the front horizontal hold. I'd hear a 'thup-thup-thup' noise both from the speaker and somewhere in the set, and the horizontal drive waveform flickers on the scope screen.
Something arcing somewhere? Didn't see anything immediately obvious.
Last thing... remember that rectifier's melted cathode connection? I just had a closer look at it. Check this out - there isn't much left of the cathode either:
Dayum, looks like this set basically had a complete meltdown in its past, must take some serious business to get that kind of sustained arcing in a rectifier. But it's all right now, it's been brought back from the dead!
