Slight shadow on my Chromacolor II picture - ideas ? - Videokarma.org TV - Video

Snade · #1 06-09-2008, 06:40 PM

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?

Thanks. Mark (aka Snade)

radiotvnut · #2 06-09-2008, 06:56 PM

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

eberts · #3 06-09-2008, 07:04 PM

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.

Tony V · #4 06-09-2008, 10:00 PM

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

jpdylon · #5 06-09-2008, 10:43 PM

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.

Tony V · #6 06-09-2008, 11:33 PM

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

radiotvnut · #7 06-09-2008, 11:58 PM

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.

*zenithfan1* · #8 06-10-2008, 09:45 AM

I think it's the bad cap too.

rcaman · #9 06-10-2008, 10:31 AM

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

Snade · #10 06-10-2008, 10:33 AM

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

The CC II picture is pretty amazing.

kbmuri · #11 06-10-2008, 11:42 AM

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.

Tony V · #12 06-10-2008, 11:50 AM

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

Snade · #13 06-10-2008, 12:07 PM

Quote:

Originally Posted by Tony V

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

kbmuri · #14 06-10-2008, 05:49 PM

I always try to rule out the simple things

. Ok, replace the capacitor.

kbmuri · #15 06-10-2008, 05:54 PM

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...