Run capacitor replacement
 

Okay, my daily watcher has been acting up lately and I think the run cap is on its way out. I pulled the back of the set and felt it; very warm, bordering on hot. It's a 3.5 microfarad, 440VAC oval can. I've been checking around and the closest oval can run cap I can find is 4 microfarads. I'm just wondering if one of these would be a suitable replacement.

Dumont set?

Or a Zenith Duramodule set? They used a ferroresonant supply with the cap. I my have one or two old-stock.

For the Zenith colors IIRC they are all the same.
Probably the same on other brands too.
Symptoms are if opened pulsating pix. Shorted
fast breaker pop.

73 Zeno:smoke:
LFOD !

The capacitor used with a CV transformer forms a resonant circuit with the winding driving it. The value is critical to proper operation, so I would really suggest finding a 3.5 uF if at all possible.

Oh, I didn't know the type of TV mattered. It's my 1976 Electrohome C31 chassis console.

Seems to be a popular value for ceiling fan box-style capacitors, but oval cans are practically non-existent.
Yup it pulsates a bit, mostly noticeable when looking closely at letterbox presentations. Often times it will pitch a fit and brightness will go down and back up repeatedly. Sometimes the picture will tear a bit. It was well-behaved for most of last night though.

:scratch2: A separate winding and a two amp fuse for a couple of pilot lights ? Strange ....

Allows for instant on - the winding for the CRT filament can be powered while the set is off. The lamps would need a separate winding.

I have an old stock Zenith - it comes with a mounting clamp as well.

Cool! So these don't go bad from sitting like electrolytics?

Ahh, so that's why there's a separate winding. This set has an "Instavu" switch on the back. I have it turned off though.

Nah - They are hermetically-sealed and oil filled (hence the "no PCBs" label), and are not affected by aging as much as an electrolytic. These types of caps are in most every home air conditioning system - the one in my Rheem gaspack right now is a Zenith cap - put there while troubleshooting a no fan start problem (Cooling coil would freeze up). I swapped in the Zenith cap to replace a 4uF cap, but the problem turned out to be bad solder joints at a molex connector on the system control board. I was hot, so a quick resolder and then I buttoned it up once it was going - the Zenith cap left in the unit.

Right on, and it will be good to know the Zenith part number in case the replacement ever goes bad. After all, this set is ran several hours a day.

PM sent.

Those Zenith Chromacolor II can capacitors (22-7126-01) are available from TEDSS.com. The only place I've been able to find them. It looks like Zenith contracted those out to York air conditioning. TEDSS says they're slightly dented. The two I ordered had tiny dents like there were a bunch stored loose in a big box, not crushed or anything.
http://www.tedss.com/2020038517

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.

Those lines are not caused by the VRT resonant cap...All that cap does is regulate the AC output voltage on from the power transformer...The rectifier and filter cans would catch any noise the VRT cap could make.

Vertical lines are usually a horizontal problem, video problem, or bad filtering effecting one of those stages.

The Zenith is probably loaded with bad caps, including the VRT cap. Its picture is dreadful. I saw a video of the restoration of a similar one, also full of bad caps.

I suppose the next thing I'll do to the Electrohome is replace the two big filter caps just forward of the VRT.

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.

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/

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.

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.

Nah, this is another cap, under the chassis:

My bad, lost context.

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.

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.

"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.

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.

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.

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.