Rca 8-pt-7031

[dtvmcdonald]

Last night, while I was examining the video amp response, the picture died.

Too-low HV (about 1700 volts) and a variable buzzing sound from what appears
to be the horizontal output box. I can't tell if it is in the transformer or at the
rectifier socket.

To make a long story short, the buzzing disappears if I remove the HV rectifier.
The waveform at the CRT anode connector shows aperiodic dips, a dozen of so
horizontal periods apart. This does not change if the CRT base is plugged in or not.
Similar glitches appear at the HOT plate cap.

I removed the HV box and found little visibly amiss. There was a little black crud
on the insulating material covering the tube socket, which I removed. No difference.
The audible noise and glitches disappear entirely if the HV rectifier is removed.
They are reduced but still there if I disconnect the CRT anode connector.

I did notice that one pin (a filament one) of the HV rectifier tube socket was filled with the waxy stuff, which I cleaned out with no change.

Tests show that with or without the HV rectifier tube the boost voltage is normal.
With HV rectifier removed the pulses at the HOT plate appear reasonably
normal, with the rectifier in, they are low. My HV probe has only a rough calibration
for frequencies above 1 kHz.

I then removed the wires to the yoke. The buzzing was much less prominent
but other symptoms appeared similar, with or without rectifier tube, except that the
glitches became somewhat more regular, varying with the vertical hold (not signal applied) but not at all in sync with it. (Due to variation is current draw from the boost?)

Removing the wires to the width coil removed the boost voltage and the large
single cycle HV pulse at the HOT plate cap.

The HOT gets warm, but no sign of distress and its not really "hot" as opposed to warm, and I don't think its warmer than when the HV was OK.

So the question! I've never had to service a problem like this before. Should
I first assume that the problem lies with arcing under the wax (?) covering the
HV rectifier socket, including the filament dropping resistor? Should I remove that
covering to examine what's under it? Is it really wax, its rather hard for wax.
Its a tan color. How do I remove it? Heat gun to melt it, solvents, chipping???

What are the experts recommendations?