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Old 03-05-2011, 10:05 PM
mt999999 mt999999 is offline
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Exclamation RCA-Victor 21-T-8428 TV - Help!

Hello all... I'm new here and I am hoping someone could help me. I found an antique RCA 21T8428 television in my cellar and I decided to plug it in... bad idea. I got sound to come out (I plugged up an analog cable line through an adapter) and tried to tune in a picture. A few minuets later it smelled awful and white smoke was pouring out what I believe was the power supply box. There was audiable poping and cracking, but it was still running. All the tubes were lit. I forgot to mention I had to wire on a new cord... perhaps my Grandma cut the plug for a reason. I want to know if I destroyed the power supply, or if it was already broke, or if that isn't it? Perhaps I should have replaced some caps first... thanks for the help!
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Old 03-06-2011, 01:57 PM
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Jeffhs Jeffhs is offline
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The cord was cut off on this TV set for a good reason--there are one or more short circuits or other very major problems somewhere in the chassis.

It is never a good idea to plug a very old TV or radio, stereo console, etc. into AC power and turn it on before replacing, at very least, the electrolytic filter capacitors in the power supply, the first step in a procedure followed in television/radio restoration known as "recapping". If the TV you found has a power transformer, shorted filter capacitors can damage or destroy it and/or the low-voltage rectifier tube if the power supply is not fused, or if the fuse has been bypassed or replaced with one larger than the original. If you see white smoke coming from "the power supply box", which I am guessing means the high voltage cage, your TV's flyback transformer may be shorted and will have to be replaced, although there is a fuse in the high-voltage cage that is supposed to protect the flyback in the event of major shorts, say in the horizontal-output tube.

Any number of components in the set could have burned out or been destroyed when it started smoking. If you pulled the plug as soon as you saw the smoke, there may not be too much damage, but I wouldn't count on it; the longer the set was on the greater the damage will be. If you saw clouds of white smoke coming from what you refer to as the PS box (again, I'm guessing--I don't know if you mean the HV cage or the area in which the TV's power transformer, if used, is located), there is a very major short in the set; needless to say, this TV must not be used again until it is recapped, at least in the low-voltage power supply. Again, damage of varying degrees may have occurred in other parts of the set as well. You are very fortunate that the set did not catch fire.
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Last edited by Jeffhs; 03-06-2011 at 02:12 PM.
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Old 03-06-2011, 02:38 PM
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Eric H Eric H is offline
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It probably was a Filter Cap venting, probably not too much damage.

Depending on whether this is a Transformer set or a Voltage Doubler Power Supply it could just need new Caps, worst case is a burned transformer but usually takes out the 5U4 first.

If it uses a 5U4 Rectifier tube(s) you could remove it and power it up again briefly, if the heaters light and nothing smokes then the transformer is probably OK.
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Old 03-06-2011, 04:35 PM
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Mt9999 you did the best thing ! It was fun to watch - as long as you stood back, and in very short order you found the problem..... You know when I learned tv repair whenever a flyback was about to smoke up our instructor turned off the lights and we all gathered around and watched the show!!! You didn't do anything wrong, and the set will live again. Now even if you don't know much about electronics, you know there was a problem with that thing that smoked..... Welcome and have fun !
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Old 03-08-2011, 07:02 PM
mt999999 mt999999 is offline
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Thanks everyone for the help... I hope it is only "minor damage" done. I should have thought more into it, this is the first time I've worked with vintage televisions. I've worked a little with AA5's, but no power supplies in those. I have not yet given up hope, I will still tear it apart and replace the paper caps, and see what happens. Any more suggestions? I'd also like to add that I poped a cap while adjusting the horizontal control, but I am positive this has nothing to do with it smoking, that was when I first plugged it in, and It only smelled a little, no smoke.

I'd also like to say that it has been in the basement since the mid 60's, not powered on since the 70's, and we have had multiple floods of the cellar. I'd imagine the components would be up high enough to not be damaged, but water might be shorting it out... but the loud speaker which is lower than that still works fine. I was told to run a hair-dryer on it, but I want to ask you guys first. Thanks again!

And the smoke wasn't billowing, but I know I wasn't imagining it. It was light and thin, and I pulled the cord ASAP. It almost sounded like water drops hitting a hot stove, sizziling. The box I was calling the power supply is probably the high voltage cage, please excuse the ignorance in names. It had a high voltage warning to the service man and a warning about the picture tube.
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Old 03-08-2011, 10:07 PM
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I guess we've all done the same thing. About 10 years ago I man gave me a similiar RCA which had been stored in an unheated building for about 10 years. He told me it worked fine so as soon as I got it home I plugged it in. Same results: smoke, accompanied in my case by angry sounds from the power supply. A filter cap had let go. No real harm done, though. After a recap it worked nearly as good as new.
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Old 03-08-2011, 10:11 PM
Dude111 Dude111 is offline
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Welcome ashore my friend
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Old 03-09-2011, 08:47 PM
mt999999 mt999999 is offline
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I'd also like to ask if anyone knew where to find capacitor replacements, like paper electrolytic. I have tons of the tiny ceramic ones (again with the names) but not electrolytic replacements. I'd love to have a manual too, thanks again.
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Old 03-09-2011, 09:34 PM
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bandersen bandersen is offline
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JustRadios, Allied Electronics, Digi-Key and Mouser all have a good selection of both plastic film and electrolytic capacitors. Just search to web for those names and you'll find their websites.

This set is covered in Sams Set 398, folder 2. I don't have a copy, but many someone else does ?
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Old 03-10-2011, 12:11 PM
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Quote:
Originally Posted by mt999999 View Post
Thanks everyone for the help... I hope it is only "minor damage" done. I should have thought more into it, this is the first time I've worked with vintage televisions. I've worked a little with AA5's, but no power supplies in those.
There are power supplies in AA5s but they are much smaller than those in TVs, since in an AA5 radio there are no very high voltages (in the thousands of volts) as there would be on a television CRT (the highest voltage I've ever seen in AA5s is perhaps 250-300 volts maximum for the B+). Another clue that AA5 power supplies are nowhere near as powerful as TV ones is the fact that many small radios have an equally small rectifier tube; most of the time it's a 35W4 in AC-DC sets, but transformer-powered radios use more robust rectifiers such as 5Y3, 6X5, et al. Zenith radios of the '30s were notorious for power supply troubles (often burned out power transformers) caused by heater-cathode shorts in the 6X5 rectifiers. I believe the company eventually issued a service bulletin addressing this problem, advising technicians to replace 6X5s in these radios with tubes having wider spacing between the heater and cathode to minimize the chance of shorts.

BTW, if the smoke you saw in your RCA TV was white and not billowing out of the HV cage, I would agree with others here who have said that the problem may be no more serious than an old and defective (likely shorted or close to it) filter capacitor venting. Replace that one and any other old caps in that set (as a matter of routine in very old sets such as yours) and it should be OK, as long as you didn't leave it on for any extended length of time after you noticed the problem.

Good luck. I think you will be pleased with the results once you get this set working, as these older sets were built much, much more solidly and had much more conservatively rated components than today's sets, many if not most of which are built in such a way as to push the components right up to their limits. It is little wonder many of these TVs fail after only a short time (read a year or less), as the cheaper off-brand ones. If I were going to purchase a new FP TV today, I'd probably go with either an RCA (because I already have an RCA 19" analog set that has given me trouble-free service since it was new 11 years ago, and still works amazingly well today) or a set in Panasonic's Viera line. I would avoid most other sets with brand names I never heard of like the plague, as one often has no way of knowing who actually built them, let alone the reputation (or lack of it) that company has for quality.
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Last edited by Jeffhs; 03-10-2011 at 12:27 PM.
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Old 03-10-2011, 02:45 PM
mt999999 mt999999 is offline
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Thanks again all! I will have to check those sites for capacitors for the electrolytics in the power supply. I also heard I need to replace pretty much every other paper cap to get a good picture like it was new. I will assume that the ceramics are still good. I would like to know where to get a color code chart for them, assuming there was a standardized one over the years, in case anyone has a link or something.

I also know the other old AA5's have small power supplies, but I thought the ones in the 50's and 60's were designed without to make them cheaper. I heard they were grounded to the chassis or something and this is why they are dangerous. I have been shocked by an old Westinghouse AA5 from 1954 a few times.

"Many early examples of the 'All-American Five' posed a shock hazard to their owners. Lacking a mains transformer, the chassis of the AA5 radio was directly connected to one side of the mains electric supply." I'm might be wrong, but I am just quoting Wikipedia.

I would love to use this set in the cellar in my sitting area on a regular basis if I can get it working. I have faith in myself now, and I guess that's what counts. I do agree atleast the picture tube in those flatscreens goes after a year or two. Waste of money.
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Old 03-11-2011, 09:10 PM
mt999999 mt999999 is offline
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Quote:
Originally Posted by Eric H View Post
It probably was a Filter Cap venting, probably not too much damage.

Depending on whether this is a Transformer set or a Voltage Doubler Power Supply it could just need new Caps, worst case is a burned transformer but usually takes out the 5U4 first.

If it uses a 5U4 Rectifier tube(s) you could remove it and power it up again briefly, if the heaters light and nothing smokes then the transformer is probably OK.
I have the back off and it is infront of me. It has a 5U4-GB low rectifier tube and the high voltage rect. is labled 1X2B.

What do you suggest I do?
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Old 03-11-2011, 09:32 PM
mt999999 mt999999 is offline
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The box I was calling the power supply box has warnings about a fragile glass picture tube all over it. I opened it up and I guess the tube inside is the picture tube. There is a sort of capacitor with an odd orange plastic-like ring around it. Some of it appeared to have melted and driped onto the metal cage below. The horizontal output tube is connected to the capacitor-thing inside, as well as the large tube in the center. The picture tube as well as the capacitor-thing are in a metal cage-box (power supply box -- as I was calling it). Can someone give me some insight on this? This is the box that appeared to be smoking. I'd also like to add that the picture on the screen was blinking while the set was smoking. Is this a whole different problem? Thanks!
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Old 03-11-2011, 09:34 PM
mt999999 mt999999 is offline
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Quote:
Originally Posted by mt999999 View Post
The box I was calling the power supply box has warnings about a fragile glass picture tube all over it. I opened it up and I guess the tube inside is the picture tube. There is a sort of capacitor with an odd orange plastic-like ring around it. Some of it appeared to have melted and driped onto the metal cage below. The horizontal output tube is connected to the capacitor-thing inside, as well as the large tube in the center. The picture tube as well as the capacitor-thing are in a metal cage-box (power supply box -- as I was calling it). Can someone give me some insight on this? This is the box that appeared to be smoking. I'd also like to add that the picture on the screen was blinking while the set was smoking. Is this a whole different problem? Thanks!
Also, If you guys want pictures, I can figure something out.
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Old 03-11-2011, 09:46 PM
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Quote:
Originally Posted by mt999999 View Post
The box I was calling the power supply box has warnings about a fragile glass picture tube all over it. I opened it up and I guess the tube inside is the picture tube. There is a sort of capacitor with an odd orange plastic-like ring around it. Some of it appeared to have melted and driped onto the metal cage below. The horizontal output tube is connected to the capacitor-thing inside, as well as the large tube in the center. The picture tube as well as the capacitor-thing are in a metal cage-box (power supply box -- as I was calling it). Can someone give me some insight on this? This is the box that appeared to be smoking. I'd also like to add that the picture on the screen was blinking while the set was smoking. Is this a whole different problem? Thanks!
The box is most likely the horizontal / high voltage circuit. It drives the horizontal portion of the picture and generates the 1,000s of volts for the picture tube.

That thing with the ring is most likely the flyback transformer. It generates the high voltages. They have a wax coating that can melt and drip over time.

I just happened to have put up a video on YouTube tonight where I go over a late 40s TV and point out what each part does. here's the link: http://www.youtube.com/watch?v=u1r8Us8FsYQ
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