My CT-100 lost HV (from losing one B+ line).

[dtvmcdonald]

It did it again.

As Murphy's law says, my CT-100 really is sick.

The fuse M3 blew again today. I had run the set for two hours, no problem.
After an hour off I turned it on again. It behaved exactly like the last time
the fuse blew: I turned it on, after 15 seconds sound appeared.
After about 60 seconds in this case snow appeared (the modulator was off).
Almost exactly 1 second after snow the fuse blew. Is roughly 75 seconds
total normal warm-up time? It has always been exactly the same. If your
CT-100 takes less than a minute to get a raster, maybe there really is
something wrong with mine, likely in the horizontal.

The first time there was a "snap" when it blew, today, no pop at all.

This is the 375 volt line. Pete Deksnis described, as far as
I can tell, in a recent article all the places it is used, except for the three CRT
screen pots and the vertical osc and output (but maybe the output only).

This is going to be a bitch to fix its intermittent. What do you folks suggest?
The only really likely suspect is a short to ground in one
of the screen pots. Do you agree? Another possibility is a short of pins
3-4 of the ballast ... but this connects the AC from the power transformer
to the 375 volt line directly after the fuse ... I would have expected magic
smoke the first time it happened as it stayed on for maybe 30 seconds.
There was none.

A short to ground at the bottom of the three screen pots would only
generate about 80 mA, not enough to blow the fuse.

A dead short to ground at the screen of the AGC keyer would do it ... but
is not that very unlikely?

The nominal draw of the CRT divider chain, which is on this line, is only
about 30 mA, which I did later measure with a Simpson meter. I did not wait
long enough for a picture to appear as there was no fuse.

Also of course, it could simply be a loose wire or blob of solder somewhere
shorting the line to ground. Unless I'm missing someplace, every other
place the schematic, corrected as describe by Deksnis, has a 5K or more
decoupling resistor. A short to ground through 5k will smoke the resistor but
not blow the fuse.

In you folks' experience, is this a known problem?

A first proposal would be to take out and examine (take apart and clean)
all three screen pots and move the lead from pin 4 of the ballast to
a new terminal strip, install a new fuse, and try some more. Is that
reasonable?