Testing a CTC-11 horizontal hold control

[Electronic M]

I'd suspect leakage in C72 ,73 and C75 dragging the grid positive.

I've been known to manually bias (with an external PS) grids to see if that is the cause and not the symptom...

One thing my Silvertone CTC-15 clone taught me is just because something in the H system worked before things went wrong, don't mean that it did not choose to die in sync with the initial problem...That set had raster and a hint of video (but bad lytics) to start, and after a recap it was dead...Change in the H osc paper cap put it far enough out of freq. range that it shorted the damper tube (which is surprisingly vulnerable to that in that set) and boost diode.

[Kamakiri]

Originally Posted by Electronic M

I'd suspect leakage in C72 ,73 and C75 dragging the grid positive.

What operating voltage would you suggest as replacements?

[dtvmcdonald]

A couple of volts off at the Horiz Osc grid is OK ... look at the scope trace,
its 30V P-P.

That circuit is hopeless to diagnose if its not working close to properly.

Make two tests: first look at test point 60 on a scope ... is it right?

Second ... WITH THE SET OFF feed the biggest voltage square wave at 16 kHZ
your generator can muster into the plate cap of the horizontal output tube.
Scope point 61 (aka 101). You should get something ringy looking there,
problems with the horizontal output transformer or convergence
board could cause problems, especially a short on the convergence board.
(You should try the thing with and without that plugged in).

I had a fault in that circuit on my CT-100 that was fixed only
by shotgunning all, and I mean all, non-coil parts. And it was still
working ... scoping did not help.

I would shotgun everything except coils.

[Electronic M]

Originally Posted by Kamakiri

What operating voltage would you suggest as replacements?

Looking at the B+ voltages and drop I'd go 450V at least...C75 should probably be 500V or more.

Doug makes a good point...I've heard of resistors internally going open or shorted under working voltage and testing fine under lower meter voltage...If you have spares this is a very reasonable place/circumstance to shot gun.