#61
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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.
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"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#62
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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.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#63
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What operating voltage would you suggest as replacements?
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#64
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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. |
#65
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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.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
#66
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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.
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#67
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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. |
#68
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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
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"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#69
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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.
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#70
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Exactly....the resistance read correctly.
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
Audiokarma |
#71
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Thanks - good to know to still be suspicious when the resistance checks OK.
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#72
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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.
Last edited by DaveWM; 02-14-2017 at 02:12 PM. |
#73
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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.....
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"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#74
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Quote:
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
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"When resistors increase in value, they're worthless" -Dave G |
#75
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Quote:
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. Last edited by DaveWM; 02-16-2017 at 09:12 AM. |
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