|
It could be that the owner is over his head in this one. Or it could be a problem
insolvable by logic, even by a real hot-shot on the spot with good test equipment.
I have good test equipment and experience ... I had the same problem (intermittent
horizontal sync) in my CT100 --- its only real difficulty after a recap. I tried for weeks
to figure it out with a two channel scope on various pairs of places and never
succeeded, but did prove it was the oscillator itself.
It was only cured by a total, all at once, re-resistor of the horizontal oscillator.
No removed resistor tested bad either at room temp or heated with a heat gun
(at low voltage). All solder joints had previous been resoldered. So it was a
resistor changing, instantaneously, from one value to another, at voltage.
I suggest, if he can use a scope, first measure the waveforms in various places
in the sync circuit, when its working. Then first attach the scope to the plate of
the 2nd video amp and measure the waveform when the set is in sync.
Leave it attached there. Attach a zero to minus 10 or so volt bias box to pins
F and G of the PW400 board (AGC amp) and adjust so that you get the correct
signal on the scope. Leave it there and start measuring waveforms in places in the
sync circuit and the horizontal oscillator with it in or out of sync. Be patient!
That's just about all you can do to pinpoint problems unless somebody else has a
better suggestion. That's how I proved my problem was the horizontal oscillator.
Ideally this would be done with the horizontal output tube removed, as described
on p. 14 of the service notes (with schematic, at ETF) ... BUT! ... that requires
a 100W 1500 ohm resistor.
|