My recently restored Zenith roundie has developed its first problem. The vertical is acting up. The vertical is non-linear, won't stop rolling and briefly collapses to a line for a fraction of a second. Everything else seems to be alright with the set. I replaced the vertical output tube during the restoration and the set has been working perfectly up until now.

Having restored many antique radios, I was anticipating some kind of near term failure as is common when a forty plus year old piece of electronics is back in regular service. The vertical circuit does not look too complicated. One thing comes to mind, however, there is a black beauty cap rated at 0.015 uf, 1000V that I did not change. I had no replacement for it and since the set worked fine, I left it in. It is located in the feedback loop from the vertical output tube to the oscillator. The way the set is acting makes me very suspicious of this cap. This set does not seem to use hardly any of these caps, I'm surprised there are any at all. Is this a likely culprit? Any advice from experienced roundie restorers would be appreciated.

Up until now, this set has been absolutely wonderful.

Well, whatever was failing has gone completely. I have no vertical sweep at all now, just a misconverged horizontal line. I guess it is time to measure some voltages in the vertical circuits. I sure wish this had not happened. I was looking forward to enjoying this set for a while.

(For informational and educational purposes) Zenith roundies used a dual disc (3 lead) capacitor in their vertical circuits that would play hell with linearity, but I've never seen one cause loss of vertical.

Hi;

I recall back in late 1964 our family bought our first color television. It was a Zenith roundie and I believe the chassis was a 25MC33. It was an exceptionally reliable set for the most part, but I do recall sometime during the first few months we had the TV the vertical did exactly as you described. It would roll vertically and then collapse to a horizontal line and then snap back to full screen with a verical roll. This cycle would happen quite fast! I also recall hearing it "snap" everytime the picture would shrink to the line and then pop back.

I remember how amazed I was when the repair man came to the house, tipped the set over on it's side, removed the access panel on the bottom, pulled out his meter, and within 10 minutes had clipped out a defective capacitor, soldered in a new one, put the bottom back on the set and was out the door. It worked great from that day onward. Lucky for us the set was still under the manufacturers warranty.

I hope your set has a similar fairly simple problem to diagnose and repair.

Good luck with it.

Bob.

Check the vertical output transformer for a primary to convergence winding short. I have had a few fail in the last few years just like your description. It seems the insulation fails and the high voltage from the vertical output plate punches through. I have found if you cut the convergence winding out of the circuit the vertical circuit will operate but there will be no dynamic convergence. The other device with three wires is the vertical integrator and they can fail as well and cause a flat line with no vertical sweep. Sorry to hear your set is in trouble so soon and please be careful with your CRT don’t burn a line in it.
Steve

I'm being very careful with the CRT as I just had it rebuilt. I hope it is not the vertical output transformer as I expect finding a replacement might be difficult. There was a slight odor coming from the set as the vertical was failing. I plan to open it up tonight to try and figure out what's going on. I really like this set, the color quality is amazing. I never knew early color sets could look so good. My set appears to have never had any under chassis work done. With the exception of horizontal sweep tubes, tuner tubes and a few others, the set looks to be original.

why on earth would you leave a black beauty in the set when you are using it for a daily watcher. doesnt make sence to me. it would be fruitless to make any checks untill you get that bad black beauty out of there. steve

also check your service switch. but get that black ugly outta there. or you might as well put one across the ac line input and burn your house down in the meantime. steve

why on earth would you leave a black beauty in the set when you are using it for a daily watcher. doesnt make sence to me. it would be fruitless to make any checks untill you get that bad black beauty out of there. steve

I only left it in because I did not have a replacement and I've never had a set that used these before. It was not a wax paper cap so I left it alone. Most of the stuff I work on is from the Forties and I always replace the paper caps. I thought this set was new enough that it would not be a problem.

I am going to order a replacement from Just Radios so I will not have to wonder about it. I can't wait to get into the set and find out what went wrong. I sincerely hope it is not the vertical output transformer.

I only left it in because I did not have a replacement and I've never had a set that used these before. It was not a wax paper cap so I left it alone.

It is a wax paper cap encased in a plastic shroud. Guarenteed to be bad now.

As a quick test, use a few caps in series to get the cap rated at 0.015 uf, 1000V. The formula for ding series caps is C= 1/((1/c1)+(1/c2)+(1/c3)+etc), similar to parallel resistors. Best to use caps narly the same capacitence, so the voltage drop across them is close to even. The smaller cap will see higher voltage. A pair of 0.03 caps, or 3 0.047 caps would do it.

---

you said you just had the crt rebuilt well one on your guns is not making contact at the cathode and it is causing more strain on the verticle output transformer if another cathode does not make good contact it will fry your output vertical transformer. sorry i couldt help it that cap may be your only problem. everybody that is a newbie in roundies needs a good joke on them.

---

In most cases problems like this can be traced down quickly 1st check all the power supplies and then get out the oscilloscope and trace signals.

Just guessing, look for a electrolytic cap in the vertical circuit. IIRC It is a can cap. 40 uf @450 v or something close to that. Also check the vertical lin control. I have seen the lin control burn up before.
Good luck
Ed

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.

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?

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.

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.

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

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.

Moyers had the vertical output transformer:banana: 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.

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.

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.

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.

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?

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.

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,

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.

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,

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,

Thanks for looking. I will try Moyers again. They really came through for me last time. I have not been able to work on it yet. I have been busy learning to ride a motorcycle.