First Post-Restoration Glitch

[compucat]

I have had a chance to look into the vertical problem and it is indeed the vertical output transformer. One of the convergence secondaries appears to be shorted somewhere. When in the circuit, there is no vert. sweep, the two 2200 ohm resistors feeding 410V from the power supply start smoking and the transformer gets hot and emits an odor where this secondary winding connects. When I disconnect the winding, I have restored vertical sweep and everything is stable. I am going to replace the vertical transformer, the two power supply resistors and those 1000V caps as a preventative.

I think after this, it will be alright for a while.

[wa2ise]

Originally Posted by compucat

I have had a chance to look into the vertical problem and it is indeed the vertical output transformer. One of the convergence secondaries appears to be shorted somewhere. When in the circuit, there is no vert. sweep, the two 2200 ohm resistors feeding 410V from the power supply start smoking and the transformer gets hot and emits an odor where this secondary winding connects. When I disconnect the winding, I have restored vertical sweep and everything is stable. I am going to replace the vertical transformer, the two power supply resistors and those 1000V caps as a preventative.

I would think that the problem is that whatever the convergence secondaries drives has a short. Sounds like the vertical output transformer works fine when you disconnected that secondary. I'm thinking that the convergence secondary is part of the vertical output transformer, Yes?

[3Guncolor]

Sorry to hear it seems to be your vertical output transformer. It appears the insulation breaks down inside the transformer and if you look at the circuit the convergence winding is nearly at ground. The plate voltage punches through the insulation and it’s all over. I have cut apart a few of mine that have failed and that is what happened. New transformer and all is good again. I think this part is going to prove to be a week spot on early Zenith color if the set was stored in a poor environment.

[compucat]

Is this transformer a readily available part? I'm hoping I can get it from Moyer's or someplace like that. 3Guncolor it sounds like you are familiar with this failure. Where did you get your replacements?

Also, I'm quite sure it is the transformer as nothing seems out of order with the convergence panel.

[3Guncolor]

I had a few parts chassis and I found one on E-bay. I don’t know if Moyers has one but I would try them first. They found a vertical transformer for a 1971 Zenith 25” that failed just like yours about a month ago for me. I think most of the vertical transformers on the roundies around the time yours was made are very close in construction so don’t give up hope. The good news is you can still run the set without dynamic convergence. I had one that ran for over a year like that situation until I got around to fixing it correctly. Please let us know if Moyers can help you. I hope this is not going to be a weak spot for early Zenith color because I know we changed very few of them in the day at the shop I worked at so there can’t be a lot of new old stock out there. Good Luck,
Steve

[bgadow]

A sad little story: in the very early 90s I found myself with 1)lots of extra storage space, 2)lots of cheap/free sixties color sets that everyone was getting rid of & 3) a little knowledge. I had read somewhere that yokes were bonded to crt's (think later model solid state stuff). I had several good running sets with intermittent vertical problems. I thought it was a yoke problem and, further, I figured this meant the set needed a new crt and so was doomed, so I parted them out. In particular there was a 21" rectangular Sylvania console with the prettiest picture and I destroyed it because it "flatlined". Live and learn.

[compucat]

Moyers had the vertical output transformer It is a Thordarson replacement for the original Zenith part and only cost $18.00. I also ordered the two power supply resistors that burned up and I'm going to replace that black beauty I left in originally even though that was not the cause of the failure. I hope to have the old Zenith going again in about a week.

[3Guncolor]

Can't ask for better then that. Glad to hear Moyers was able to help you. I'm not aware of any major weak spots on your set.

[reeferman]

That 40 mike cap will cause the vertical to pull up from the bottom.
And to 3 gun color, thanks for saying vertical integrator in reply to my earlier answer. I couldn't think of it's name to save my life.

[compucat]

Woo Hoo - She's working again. The new vertical output transformer did it. Everything is back the way it was. I had to redo the static convergence as I bumped the crt neck components working on the set but after that, everything looks great again. I must have run the set for about six hours over the course of yesterday and no problems. In some ways I'm afraid to use it much in case something else goes. My wife seems to like the set but is skeptical that it will run for more than a month between repairs.

[compucat]

After more than a year of reliable performance the Zenith is having the same problems as before. I hoped the vertical output transformer I installed last year would last for years, it looks like I might have to replace it again. Any other Zenith roundie owners have this problem with repeated failures? I have not opened the set yet but the symptoms are exactly the same. So far all I have done to this set in the past year is touch up the greyscale. What is it about tube tv sets and vertical problems?

[3Guncolor]

Don't give up yet it may not be the same problem. I have had the same transformer problem several times on Zenith tube sets. But I have a Zenith roundie in my office at work and it has been running for years without any vertical problems. I'm hoping it's not the transformer if it is we need to find out why they seem to be failing. I have replaced the transformer several times on one set I have. I think something was causing the retrace pulse to be too high blowing through the insulation between the windings. It seems to be a weak spot for Zenith's.

[Findm-Keepm]

What's the part number for the original transformer? The Thordarson replacement? I may have one in my stash...and I'm only 30 miles or so away.

Lemme know!

Cheers,

[compucat]

Originally Posted by Findm-Keepm

What's the part number for the original transformer? The Thordarson replacement? I may have one in my stash...and I'm only 30 miles or so away.

Lemme know!

Cheers,

It is a Thordarson part #26S61. The original Zenith part number is 95-2139. If you have one that would be great. I miss the old Zenith already.

[Findm-Keepm]

Nope, I don't have it - lowest I go in Zenith 95- series is a 95-2137, and I have but one Thordarson Vertical output, a 26S75 "Universal Vertical Output" - kinda smallish.

Sorry I couldn't help - best of luck in finding a replacement.

Cheers,