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  #16  
Old 03-20-2017, 06:17 PM
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How about that? Seems Zenith supplied these to Electrohome, and at least some were made by GE. I assume the one I took out is the original considering the date code.

Next up is a .047 microfarad cap under the chassis; it's a white one. It's connected parallel across the AC line after a pair of coils.
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File Type: jpg Flip side.jpg (44.1 KB, 11 views)
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  #17  
Old 03-21-2017, 07:40 AM
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An across-the-line cap ought to be replaced with an X2 safety cap, designed to fail open rather than short. Sal's and Just Radios have them, as well as other sources. X2 for across the line, Y2 for line to ground. There is also a cap rated X2Y2 for either use.

http://www.tuberadios.com/capacitors/

http://www.justradios.com/
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  #18  
Old 03-21-2017, 04:59 PM
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I forgot to mention, there's a 2-amp fuse in series with the circuit just before the white cap. Thanks though, I'll check that out.
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  #19  
Old 03-21-2017, 05:13 PM
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Quote:
Originally Posted by Reece View Post
An across-the-line cap ought to be replaced with an X2 safety cap, designed to fail open rather than short. Sal's and Just Radios have them, as well as other sources. X2 for across the line, Y2 for line to ground. There is also a cap rated X2Y2 for either use.

http://www.tuberadios.com/capacitors/

http://www.justradios.com/
These are AC rated non-polarized oil filled motor run caps. They are used for the resonant circuit of the VRT (voltage regulating power transformer)... Modern VRT isolation transformers spec out the same type of cap as 70's SS consoles like Jon's and Zenith CCII sets do.
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Old 03-21-2017, 05:33 PM
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Nah, this is another cap, under the chassis:
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  #21  
Old 03-21-2017, 09:31 PM
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My bad, lost context.
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  #22  
Old 03-22-2017, 04:55 PM
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What's this particular white cap for though? All I know is that they should be replaced on sight. It's the only one in the set.

A couple of those coil leads look kind of toasty as well, wonder why.
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  #23  
Old 03-22-2017, 05:46 PM
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It basically shorts out any differential RF noise on the line. You could probably clip it out and not miss it...I've done that, but prefer to replace them so as to keep the original design.
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  #24  
Old 03-24-2017, 02:31 PM
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"Thanks! I ought to get a couple of spares eventually. If my 23GC45 has one - I haven't looked closely yet - that's probably going as well. Right now my Electrohome has a couple of vertical lines on the screen at all times. The Zenith gets one on the right that goes away after a few seconds."
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My 25GC45 has one, yours is the 23" version of the same chassis, so I'm sure yours does too. The value of the capacitor in those ferroresonant transformer is important, so you really need to get the right one.
It's not a standard motor-run capacitor value, the first place I looked for a replacement was electrical and HVAC supply websites. That TEDSS site is the only place I was able to find the correct part.

The cap in my set shorted out without warning after the set was on for a couple of hours. It'll pop the circuit breaker on the back when it shorts.
I replaced it with a cap I had from a parted out set, but who knows how long that one will last.

Last edited by wb2mep; 03-24-2017 at 02:35 PM. Reason: Forgot to quote post I was replying to
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  #25  
Old 03-24-2017, 02:49 PM
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Originally Posted by wb2mep View Post
My 25GC45 has one, yours is the 23" version of the same chassis, so I'm sure yours does too. The value of the capacitor in those ferroresonant transformer is important, so you really need to get the right one.
It's not a standard motor-run capacitor value, the first place I looked for a replacement was electrical and HVAC supply websites. That TEDSS site is the only place I was able to find the correct part.

The cap in my set shorted out without warning after the set was on for a couple of hours. It'll pop the circuit breaker on the back when it shorts.
I replaced it with a cap I had from a parted out set, but who knows how long that one will last.
That's okay, I already got one from Brian, and I reckon NOS units show up on eBay from time to time. If all else fails I'll use the TEDSS site.

Last edited by Jon A.; 08-25-2017 at 05:14 PM.
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  #26  
Old 08-29-2017, 05:56 AM
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Originally Posted by Jon A. View Post
What's this particular white cap for though? All I know is that they should be replaced on sight. It's the only one in the set.
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Originally Posted by Electronic M View Post
It basically shorts out any differential RF noise on the line. You could probably clip it out and not miss it...I've done that, but prefer to replace them so as to keep the original design.
It's been a couple of weeks now so I should be able to mention this without jinxing myself:

I don't yet have a replacement for the above mentioned capacitor but I wanted it out of there, plus I wanted to get a closer look at it so I clipped a lead and fired up the set without issue. Now that I knew I could go without it, I clipped it out completely. I didn't see a brand on it before, but it was NYTRONICS. I know it doesn't really matter who made these paper-in-oil abominations, but apparently that company was caught buying "scrap" from a military-spec manufacturer.

But wait, there's more...

I had been chasing an intermittent brightness problem in this set for months. Putting in new power supply and horizontal B+ caps got rid of a lot of issues, but the brightness problem persisted. Ever since I clipped out that across-the-line cap brightness has been rock solid. I never, ever thought it would be the source of the trouble, I just didn't see how. I thought they would open or short and that would be the end of it. Before I did that the problem would resurface in no more than a week whenever I tried some sort of maintenance to correct it. Most of the time it would resurface immediately. Apparently that cap was sensitive to just about everything that would touch it, electrical noise, vibrations, sudden changes in ambient temperature and who knows what else. One time it was behaving quite well for a couple of days, then when I opened the sliding door to the deck, letting in a rush of cold air, brightness dropped dramatically.
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  #27  
Old 08-29-2017, 10:42 AM
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I suppose it is possible for it to be intermittently leaky and consume enough power to drag input voltage to the set down and reduce brightness, but that somehow feels like a big stretch.

If the brightness problem persists it may be good to swap the output transistors, or at least monitor HV and gun voltages, preferably with a repeatable test pattern on screen, before and after to find out which line is changing. I mention video output transistors because on a 70's Zenith hybrid I had problems with loosing color from one gun. It was in brief intervals, and seemed to be part random, part temp and vibration sensitive....Would change as it warmed up would correct with cabinet slaps, would become insensitive to cabinet slaps but be sensitive to tuner action, would be sensitive to sound, etc. Damn thing would never have the problem when I could meter it, till it was practically permanently stuck with a dead color (took 2-3 years of living with that intermittent to get there), once I could watch all gun voltages and track the effected line diagnosis was easy.
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