This is the Zenith Chromacolor II (1975) that I picked up from Doug. I love this TV and use it all the time.

In the area I have circled below, a greenish shadow has developed on the left side of the screen. It's kind of subtle, but noticeable when the TV is showing a white background.

Any ideas?

http://www.gallagher.com/photos/2008/zenith/zenith_tv_7.jpg

Thanks. Mark (aka Snade)

Do you have a degaussing coil? It may just need degaussing.

The effect is called "doming".
Doming is a phenomenon found on some CRT televisions in which parts of the shadow mask become heated. In televisions that exhibit this behavior, it tends to occur in high-contrast scenes in which there is a largely dark scene with one or more localized dark spots. As the electron beam hits the shadow mask in these areas it heats unevenly. The shadow mask warps due to the heat differences, which causes the electron gun to hit the wrong colored phosphors and incorrect colors to be displayed in the affected area.

Wasnt there a capacitor problem in these sets that caused this symtom?
-Tony

I had the same failure on a CCII set I fixed. There is a 10uf / 450v capacitor in the power supply that opens. On most sets its part of the large multi-section can on the lower chassis.

Its failure will cause the exact symptom you're facing.

Thats what i was thinking about as i remember you mentioning it before. Thanks Jordan
-Tony

After looking at the picture better, it could be that cap. At first, I was just seeing that green spot. That 10 uF cap must have been a favorite because it was used in Zenith sets from the CCII's up through the sets of the '90's. It is a high failure part, especially in the late '70's and early '80's sets. If that section of your can is bad, do yourself a favor and change the entire can. I've learned this the hard way. Too many times, I've tried to skimp and only replace the bad section only to have another section give out in a week.

I think it's the bad cap too.

case closed it is a bad cap. it will greatly improve the pix quality when you change it. steve

Thanks a lot guys. I'll change the cap.

The CC II picture is pretty amazing.

I won't disagree with the crowd, it's probably that capacitor. However it does look like you've got an electric appliance sitting on top of the left half of the TV (most of it is cropped off of the photo). Real quick, remove the appliance and see if the green goes away. Might just be a small EM field.

That "appliance" is a Zenith radio :) I dont think that would cause it as several of us have radio's and such on top of our tv's and dont have any problems. It would seem to me if it had a magnetic field it would be across the top...not down the left side.
-Tony

That "appliance" is a Zenith radio :) I dont think that would cause it as several of us have radio's and such on top of our tv's and dont have any problems. It would seem to me if it had a magnetic field it would be across the top...not down the left side.
-Tony

Right, it's a 50's Zenith tube table top radio. I actually took it off the TV yesterday and the problem remained.

I thought it might need degaussing, so I tried the turn it on for one minute, turn it off for 20 minutes, repeat a few times, but the shadow remained. Since the greenish shadow only runs the full length of the left side, I don't think it's degaussing. Expect it is the cap based on your feedback.

One other thing, when you turn on the TV, when the picture appears in a few seconds there is lots of strong contrast for several seconds (maybe 10 to 20 seconds) and then the picture becomes normal. Is this normal warm-up? Or also a sign it needs caps replaced.

Once warmed up, the picture is fantastic, except for the shadow on the left side.

Thanks. Snade

I always try to rule out the simple things :D . Ok, replace the capacitor.:thmbsp:

I know of a very late-model Zenith (model # unknown) but probably late 90's or early 2000's that does exactly that. It's in a motel I frequent when on business travel. When you turn it on there's 5-10 second "burst" of contrast, then it's normal. I've been using the set off-n-on for more than 2 years. Hasn't seemed to have gotten worse (or better). Seems harmless, whatever it is...

I'm probably wrong, but isn't that a sign the CRT is getting up there in hours? Reminds me of TVs which don't focus well for about 15-20 seconds, when they're getting soft.

I had the same failure on a CCII set I fixed. There is a 10uf / 450v capacitor in the power supply that opens. On most sets its part of the large multi-section can on the lower chassis.

Its failure will cause the exact symptom you're facing.

Jordan, thanks a lot. Could you look at the photos below and tell me exactly where to find this 10uF cap ? Thanks.

Also, if you could recommend an online source to buy the caps, that would be great.

Mark (aka Snade)

http://www.gallagher.com/photos/2008/zenith/chromacolor_II_chassis.jpg

http://www.gallagher.com/photos/2008/zenith/chromacolor_II_inside.jpg

The cap is the big round silver can next to the power transformer, located on the flat part of the chassis. The cap will be easier to replace if you remove the chassis.

You can get new caps from www.tubesandmore.com, www.radiodaze.com, or www.justradios.com. You'll probably have to go with individual sections and attach them with terminal strips.

The effect is called "doming".
Doming is a phenomenon found on some CRT televisions in which parts of the shadow mask become heated. In televisions that exhibit this behavior, it tends to occur in high-contrast scenes in which there is a largely dark scene with one or more localized dark spots. As the electron beam hits the shadow mask in these areas it heats unevenly. The shadow mask warps due to the heat differences, which causes the electron gun to hit the wrong colored phosphors and incorrect colors to be displayed in the affected area.

I agree. I have found this doming effect frequently when I do convergence adjustments with chessboard or cross hatch patterns.

http://en.wikipedia.org/wiki/Doming_%28television%29

In some cases, a new purity adjustment might fix this problem.

Eckhard

I agree. I have found this doming effect frequently when I do convergence adjustments with chessboard or cross hatch patterns.

http://en.wikipedia.org/wiki/Doming_%28television%29

In some cases, a new purity adjustment might fix this problem.

Eckhard

That set is older than I thought, it has the delta 90d tube.
Doming usually does not affect the delta's, mostly later inline tubes with slotted shadow masks.
Probably the condensor.

Here's where the cap can lives:
http://www.audiokarma.org/forums/attachment.php?attachmentid=94966&stc=1&d=1213369087
http://www.audiokarma.org/forums/attachment.php?attachmentid=94967&stc=1&d=1213369087

Its best to pull the chassis on this one. Don't forget to discharge the high voltage before you do.

In sets with automatic grayscale tracking, you may see contrast and color temperature change for the first few seconds as the filter capacitors in the tracking circuit charge up. However, 20 seconds seems kind of long, and I don't know if this set has that feature.

The blue lateral magnet is on backwards

Here's where the cap can lives:

Its best to pull the chassis on this one. Don't forget to discharge the high voltage before you do.

Jordan, thanks a lot.

Doug is going to help me, so I won't kill myself. :D

Thanks again. Snade