Advice needed with a Monster of a Zenith

[Unimatic1140]

Well I give up guys. There is a wave in my picture and I'm having trouble determining if its being caused by a 60 cycle heater-cathode leakage within a tube or a 120 cycle filter capacitor problem or something completely else. When I first turn the set on the wave isn't visible, but then after a minute or two the wave starts appearing at the bottom of the screen then slowly travels all the way up to the top of the screen. The wave is much more vivid at the bottom when it first appears and it's hardly noticeable by the time it reaches the top of the screen. Before the wave hits the top of the screen a new wave has already started at the bottom, but I'm not sure if this is because there are two separate waves on the screen at once or if its one big wave and I'm seeing the middle of it. I turned the width of the picture all the way down so I could see the edge of the raster and it appears that there is no pulling or weaving on the sides of the picture what so ever. I also tried pulling one of the IF tubes out to kill the video temporarily to see if I still have the wave, but without any text or picture on the screen I cannot tell if its there or not. I've tried swapping most of the vacuum tubes with the originals and since I have two 19AP4 picture tubes, both of which show the wave, I was able to rule out the picture tube as the culprit. So now I'm completely stumped. Any advice on what this could be or how I might go about troubleshooting this problem would certainly be appreciated. Thanks again everyone.

[Eric H]

Did you try jumping in another cap on the B+ line and see if it goes away?


I have an Olympic that has the same symptom and an extra 100 mf on the B+ line reduces the hum bar considerably. Not sure if one of my new caps is bad or what.

Eric

[Rob]

An electrolytic cap that has excessive leakage current will do this to a circuit even when a good electrolytic is placed across it in parallel. In such cases you must remove the culprit electrolytic from the circuiit. This is why the lazy serviceman's trick of just wiring new electrolytics on the terminals of the original chassis mounted cans doesn't always work so well.

Rob

[Unimatic1140]

Thanks Guys you were right on target. I finally figured out that one of the 11 brand new electrolytic caps was not working properly. Anyway, I changed it out and I got rid of that wave, YAY! The picture now looks wonderful.

I was putting too much confidence in brand new parts. That certainly was a good lesson. When I get it all back together I will post some final pictures.