TV repair question - Videokarma.org TV - Video

TranStar · #1 03-11-2016, 04:03 AM

I have a RCA 21t9275 "Super" TV that I bought for $75 and when I plugged it in at the store the cord got extremely hot, so I immediately unplugged it. Upon further inspection I found the yoke (see pictures) just hanging loose on the neck of the crt, apparently the grommet or plastic piece that attaches to it had dry rotted. Also I found that some of the tubes in this set were not the correct type. Does anyone have have a picture of what the yoke is supposed to look like and why exactly did the tv overheat (to date I've replaced about 90% of the capacitors in this but I think they were dried out)

Olorin67 · #2 03-11-2016, 06:49 AM

For the cord to get real hot you'd have to have a real bad short somewhere. If the wrong tubes were in some sockets you could have had a short to ground, that could do it. If this set has a power transformer you will want to make sure that's not burned out before investing too much time fixing the set.

dieseljeep · #3 03-11-2016, 10:34 AM

Quote:

Originally Posted by Olorin67

For the cord to get real hot you'd have to have a real bad short somewhere. If the wrong tubes were in some sockets you could have had a short to ground, that could do it. If this set has a power transformer you will want to make sure that's not burned out before investing too much time fixing the set.

The 5U4 doesn't look too healthy.
Remove the 5U4 and just plug in the chassis. If it still draws excessive current, the transformer is history. The primary could've been damaged by lightning. There was a lot of those sets around, but most technicians didn't hang on to them. The yoke is RCA made and the cover is special to them, so you have to locate an RCA yoke.

zeno · #4 03-11-2016, 03:27 PM

If that 5U4 is white on top like it looks its JUNK &
probably the main problem.

Next for the yoke. Get some yoke wedges from almost any
modern color TV. Wedge it in place. Next get a yoke cover off an old yoke that has the 2 centering rings & the same neck size. Not
perfect but it wont be moved around so things should stay
put for a while. Both easy to come by....

The tubes with different numbers are probably good subs but
you may want to change them back sooner or later. For now
use the tube layout to be SURE they are in right !!!
Good luck

73 Zeno

Dubis7 · #5 03-11-2016, 03:52 PM

Pretty sure Bob Anderson has developed a way to fabricate new yokes. If you had a design to go off of, maybe it could be replicated?

It was something with polystyrene and a special adhesive. Should result in a reliable reproduction.

user181 · #6 03-11-2016, 04:35 PM

Quote:

Originally Posted by Dubis7

Pretty sure Bob Anderson has developed a way to fabricate new yokes. If you had a design to go off of, maybe it could be replicated?

It was something with polystyrene and a special adhesive. Should result in a reliable reproduction.

Would this be a possible candidate for 3D printing? Or would the environment be too hot?

dieseljeep · #7 03-12-2016, 09:08 AM

Quote:

Originally Posted by user181

Would this be a possible candidate for 3D printing? Or would the environment be too hot?

IIRC, the yoke was special to RCA, as well. It uses center-tapped horizontal windings. I don't think any 110 degree yoke would work properly, just the original.
I also used plastic food containers, close to the right diameter for the cover. Spray paint it black.

TranStar · #8 03-13-2016, 01:21 PM

update: the crt in this set doesn't seem to plug into the molex connector correctly and the text on the neck does not say 21cep4 so i think somebody also threw a random picture tube in this set, does anybody know where i can get a 21cep4

tom.j.fla · #9 03-13-2016, 02:02 PM

Hello, The tube that you have in your set maybe a good sub as in the day shops had to use tubes they could get or had on hand. If you do not have a tube sub book you can find two and the 1968 RCA tube manual in the free downloads file at www.smcelectronics.com go to parts & accessories menu then go to downloads scan down to vacuum tube info and find the e-books there. All the best,Tom

TranStar · #10 03-18-2016, 04:31 PM

UPDATE: i got a new 21CEP4 for this set as well as a new 5U4GB.All i think i have to do now is finish re capping this set and get a few more tubes and it will be good to go. on a side note, does anybody know of a cleaner you can use on tinted glass that wont leave streaks

zeno · #11 03-19-2016, 12:29 PM

Quote:

Originally Posted by TranStar

UPDATE: i got a new 21CEP4 for this set as well as a new 5U4GB.All i think i have to do now is finish re capping this set and get a few more tubes and it will be good to go. on a side note, does anybody know of a cleaner you can use on tinted glass that wont leave streaks

We used pure ammonia & water about 5 pt water 1 pt ammonia.
Also REAL TSP works good.
Dont add soap !

Electronic M · #12 03-19-2016, 01:50 PM

Quote:

Originally Posted by TranStar

UPDATE: i got a new 21CEP4 for this set as well as a new 5U4GB.All i think i have to do now is finish re capping this set and get a few more tubes and it will be good to go. on a side note, does anybody know of a cleaner you can use on tinted glass that wont leave streaks

Don't clean the black aquadag off the funnel/bell of the CRT behind the screen...That serves an important electrical purpose and needs to be present.

TranStar · #13 03-20-2016, 11:23 AM

on another note, does anybody know where i can find new .00082uf and 1600v or higher capcitors. the originals of that value in this set are the el menco type and those are ticking time bombs

TranStar · #14 03-25-2016, 04:28 PM

UPDATE: I plugged the tv in for the first time after being recapped and the cord did not overheat this time. although does anybody have a picture or diagram of what wires go to what connection on the crt, mine has an eight pin molex connector yet on the crt it has 7 pins in a way that one pin is left out in the circuitry i just don't know which pin

dieseljeep · #15 03-26-2016, 11:30 AM

Quote:

Originally Posted by TranStar

UPDATE: I plugged the tv in for the first time after being recapped and the cord did not overheat this time. although does anybody have a picture or diagram of what wires go to what connection on the crt, mine has an eight pin molex connector yet on the crt it has 7 pins in a way that one pin is left out in the circuitry i just don't know which pin

It looks like the chassis has that funky nylon type CRT socket. It should have a keyway. The keyway designates pins 1&8 on the CRT.
Is the plastic key and base missing from the CRT? There should continuity between two adjacent pins. That designates pins 1&8, the heater.