Testing a CTC-11 horizontal hold control

[Kamakiri]

Okay, same result. I think it's time to go looking elsewhere and go back further.

Tested voltages at V11, the horizontal oscillator (6CG7). Looking for a -.8v on pin 2. Fired the set up, and had that -.8V, but as it warmed up over 20 seconds or so, it decreased to zero and went to a positive .8V. The next thing back in the chain that I would normally go after would be the AFC diode, but I already replaced that.

Now I'm clueless.

[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.

[Kamakiri]

Just on the oscillator board, or how far do I go?

I've never seen a resistor do that, but it would make perfect sense if it's a condition that could reasonably occur.

[dtvmcdonald]

A resistor most certainly did exactly that after warmup, on my CT-100,
in exactly that circuit. I never got it to do it outside the circuit
(testing with DC) after I removed them. I never knew which one it was.

Perhaps it the high voltage pulses.

[Kamakiri]

Welp, the set's fixed!

After rebuilding almost everything in the whole set, I asked my buddy Ed to give it a whirl. He couldn't find ANYthing wrong with it. He re-checked the horizontal hold control and the sine coils, and both were fine, but he tried subbing them anyway. Horizontal hold control, nothing. Sine coil, bingo. That did it. The sucker tested fine but was the problem in the end. He jigged it up in an 11 he has at his house, and it's got a beautiful picture and everything locks in solidly.

Man, some of these things will drive you to drink....but I sure did learn a lot in the process

[old_tv_nut]

Hi, could you explain what tested fine on the sine coil? Was it the resistance that was OK? For example, I don't think a shorted turn would necessarily test bad for overall resistance.

[Kamakiri]

Exactly....the resistance read correctly.

[old_tv_nut]

Thanks - good to know to still be suspicious when the resistance checks OK.

[DaveWM]

odd, I wonder if the sine coil was not making good contact at the pcb? generally you can short those out and the will still work ok, in fact IIRC shorting and unshorting while adjusting them is a way of setting them up.

[Kamakiri]

I reworked every solder joint in the whole PW600 section, that was one of the things that I did early on, then redid. All I know is at this point, I have a CTC-11 with one hell of a lot of new parts

This set originally came from Dave A. Here's a shot of it when I first picked it up at Dave Goodling's in Lancaster PA back on Feb 20 last year.....

[DavGoodlin]

Originally Posted by Kamakiri

This set originally came from Dave A. Here's a shot of it when I first picked it up at Dave Goodling's in Lancaster PA back on Feb 20 last year.....

Great job Tim. I agree that coil issue was perplexing, since shorting that coil is S.O.P. on CTC12 and later chassis to center the hold control range. Not so on the CTC11, this coil is center-tapped - an auto-transformer to feedback from plate to the osc grid, so you don't short it because of how critical this loop is. The adjustment is in the Sams 550-2, page 16 and requires a scope to match amplitude of the two peaks.

I would not mind putting that coil on two of my ring-testers to see if that fails the coil against a good one from my working '11, the resistance measurements sure didnt

Is that CRT a 21FJP22, or has it a formed safety glass for the 21FBP22? I covered it up and did not peek so I wasn't tempted to keep it

[DaveWM]

Originally Posted by DavGoodlin

Great job Tim. I agree that coil issue was perplexing, since shorting that coil is S.O.P. on CTC12 and later chassis to center the hold control range. Not so on the CTC11, this coil is center-tapped - an auto-transformer to feedback from plate to the osc grid, so you don't short it because of how critical this loop is. The adjustment is in the Sams 550-2, page 16 and requires a scope to match amplitude of the two peaks.

I would not mind putting that coil on two of my ring-testers to see if that fails the coil against a good one from my working '11, the resistance measurements sure didnt

Is that CRT a 21FJP22, or has it a formed safety glass for the 21FBP22? I covered it up and did not peek so I wasn't tempted to keep it

is it the sine coil or the horz freq coil that was the issue. the labled sine coil does not have a center tap. Which one is the horz hold anyway, from the attached schematic there is a sine coil (no tap) labled horz hold and then there is the taped "horz freq" labled coil. IIRC the tapped one is the horz hold control mounted for user access and the sine is not, just mounted on the pcb.


hmm looked at again, I just must be mis rembering, sure looks like the sine labled coil is off pcb and is indeed the horz hold control.
Just checked the manual, I see there were changes in how those coils were used.