I love my roundie but it sure is high maintenance. - Videokarma.org TV - Video

compucat · #1 10-25-2010, 11:51 AM

I recently replaced an electrolytic cap that went bad and got the old Zenith 25MC33 working again. Just the other day the vertical hold went way off and when I adjusted it back in the height had pulled in from the top and bottom about a quarter of the screen. I have noticed a blue glow in the vertical output tube. Can a gassy tube cause this? I turned the set off and on again and the picture returned to normal for a while. Also, it now occasionally comes on like the brightness control is way up, not all the way or with retrace lines. If I turn it off for a minute and then on again it is normal. It still has a lot of original Zenith tubes still in it.

kx250rider · #2 10-25-2010, 01:24 PM

A couple of thoughts... It sounds like a complete re-cap might save you a lot of headaches later. At least all the rest of the electrolytics, and any of the brown shiny Sprague paper caps. As far as the blue glow, that can be caused by air leaking into the tube, or too much current load across the tube (more likely the latter). That Zenith is a good chassis, but it's still 45 years old, and that technology, while the best at the time, did require a fair amount of babying.

Charles

miniman82 · #3 10-25-2010, 11:45 PM

A set I'm working on now has some seriously drifted resistors that pull into spec once the set has been in operation for a while. Might be worth poking around with some cold spray on your set, to see if maybe the same thing is happening to you? Also second the recap.

andy · #4 10-26-2010, 12:41 AM

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miniman82 · #5 10-26-2010, 01:18 AM

Totally agree, though my CTC-9 displayed a fine picture before I even replaced the 'lytics. Some sets just have lower quality parts in them, that's all.

oldtvman · #6 10-26-2010, 09:01 AM

Back in the day those were the kind of problems that kept shops busy. Color sets of the time required more attention than the sets of today. It was a great time.

Phil Nelson · #7 10-26-2010, 10:41 AM

If it ran 45 years with original electrolytics and mostly original tubes, I'd call that pretty low maintenance.

I'd replace the electrolytics and then see where you stand. They are so frequently bad that I don't bother trying to diagnose problems until they have been replaced.

Just my $0.02.

Phil Nelson

compucat · #8 10-26-2010, 11:07 AM

Quote:

Originally Posted by oldtvman

Back in the day those were the kind of problems that kept shops busy. Color sets of the time required more attention than the sets of today. It was a great time.

I agree that it was a great time. My tube type black and white sets are generally more trouble free than the tube color set simply because of the tube and parts count. Of the non electrolytic caps, which ones are in the league of paper caps and should be replaced? I know the black beauties and any bumblebee caps must go. The Zenith has many that look like orange drops but they are either brown of maroon colored. Are these to be replaced too? I hope not as there are a million of them.

compucat · #9 10-26-2010, 11:10 AM

Quote:

Originally Posted by Phil Nelson

If it ran 45 years with original electrolytics and mostly original tubes, I'd call that pretty low maintenance.

Phil Nelson

It has spent probably at least a decade out of service. It was lonely and unloved when I bought it from Harry Poster about four years ago. Since restoring it in 2007 I have tried not to put too many hours on it although I do use it frequently for no more than about an hour or two at a time. My black and white tube TVs and my tube radios I run the heck out of them.

Phil Nelson · #10 10-26-2010, 11:54 AM

I view the "maroon drops" as a sort of in-between category. My RCA roundies still have a lot of originals, but I have replaced some, too. I would replace the electrolytics and then approach the maroon guys on a case-by-case basis. A more risk-averse person would shotgun all of 'em, I suppose.

The consequences of losing an electrolytic can be dire, depending on which one goes poof. With those, I show no mercy.

Phil

oldtvman · #11 10-26-2010, 04:29 PM

Quote:

Originally Posted by Phil Nelson

If it ran 45 years with original electrolytics and mostly original tubes, I'd call that pretty low maintenance.

I'd replace the electrolytics and then see where you stand. They are so frequently bad that I don't bother trying to diagnose problems until they have been replaced.

Just my $0.02.

Phil Nelson

Phil, I remember ctc series eating flybacks in the day, others had different problems, the Admirals also ate flybacks, but most problems boiled to dirty controls bad switches dirty tuners all of which could cause weird problems sometimes if you weren't familiar with servicing that peticular brand. Most people would set there and watch color pictures that were severely out of adjustment probably because they were never instructed how to set the controls up properly.

Findm-Keepm · #12 10-28-2010, 06:24 PM

Quote:

Originally Posted by Phil Nelson

I view the "maroon drops" as a sort of in-between category. My RCA roundies still have a lot of originals, but I have replaced some, too. I would replace the electrolytics and then approach the maroon guys on a case-by-case basis. A more risk-averse person would shotgun all of 'em, I suppose.

The consequences of losing an electrolytic can be dire, depending on which one goes poof. With those, I show no mercy.

Phil

The maroon caps were Arco-Elmenco (the "EM" that's printed on them). Arco made some very good caps -with the quality of the orange drops. I've replaced only one - a mouse had peed on the circuit board and corroded the lead. Arco is still in business, making specialty caps and silver micas. They got the Sangamo fabs for silver mica caps years ago and have been cranking them out ever since.

The Zenith sets of this vintage had the wonderful blue ceramic discs. Not so wonderful in the temperature coefficient - the tempco on some is N2200 - pretty drifty. I recapped a 20Y1C38 chassis - typical Zenith - replaced e-lytics, including the vertical cap up under the chassis - it's in a clamp near the front of the chassis. And I replaced all but one of the blue ceramics. I left the big white ceramic 1000V Elmenco cap in place - it's still there. Rock solid set, and still going in the parlor of an older guy I used to work with.
Zenith finally started replacing the spare blue ceramic caps stock with Erie and RMC caps - I've got some NOS blue ones and Erie ones - dunno when they started the transistion.

Steve, if you go the way of a complete recap, gimme a shout-out via PM. I've got some of the caps and you are right down 58 from me.

Cheers,

ctc17 · #13 10-28-2010, 10:06 PM

Guess what....I got a 25MC32! Good crt but the damper red plates and no HV.
I also have a 25MC36 rectangy and it has been super reliable.

I can t wait to get this thing running. Its such a cool looking set.

holmesuser01 · #14 10-29-2010, 09:47 AM

I got my first roundie, a CTC-10C, in 1974. So, it was 14 years old. CRT was broken, and a few tubes missing. I also got a CTC-11 chassis from the same guy. Also, missing a few tubes.

Installed a used CRT, an FBP, and tubes, and it came to life. It ran good, not great. In 1984, I installed a brand new FBP CRT. I had no idea that there was a difference in the FBP and the CYP that it came with. I used the set daily for almost 10 years.

In 1995, I replaced several OEM tubes, and some of the electrolytics, and it plays on.

I imagine that it is too late to find a 21CYP22 tube for this set, so it runs OK with the FBP and no modifications.

I dont run it much anymore, but, I do run it now and then. It's connected to the satellite, and the picture is still good with good linearity and color. The tuner needs some attention, so when I pull the chassis, I'll check it over.

It's the only CTC-10 that I have ever worked on. It seems to be built better than the later stuff like the 12's and on up.

I've worked on one Zenith roundie. It had something going on that would kill the damper after a few hours of playing. I was just beginning to work on tube stuff at the time, and it baffled me. I had it sitting in the showroom in my shop for years.

I know people that had roundies back in the day, and it was a normal occurrence to see the TV repair shop truck in their driveway. That said, I have an aunt that had a RCA CTC-16X that ran from 1964 to 1978 and never had the back removed for any reason. She replaced it because the colors weren't perfect anymore, and she wanted a new Magnavox in a pretty cabinet. She had the Maggie serviced alot, that I remember.

Those were the days.

Bruce

compucat · #15 10-29-2010, 11:08 AM

Quote:

Originally Posted by Findm-Keepm

Steve, if you go the way of a complete recap, gimme a shout-out via PM. I've got some of the caps and you are right down 58 from me.

Cheers,

I probably will go with a complete recap. This set is in regular service and has been for the last three years. I know you are not too far from me. You sent me a rod antenna for a 1970s GE 12" black and white a long time ago and that set is still in regular use.