Glowing colors on screen

[SavannahLion]

Not really arcade related but thought I should ask.

About ten err... maybe fifteen years ago... maybe even longer  My mother purchased a large screen Zenith CRT TV. Over the first five years of its life, the TV saw several repairs such as full replacement of the main PCB and a tube replacement (probably). When the tube was replaced (or whatever) an interesting symptom cropped up. After watching the TV for any extended length of time and switching it off, three color smears would be apparent on the screen. A blue, red and I think a green smear at different locations. When we asked the repair tech, we were told it was due to "hyper-active" phosphors inside. At first, the smears would take an hour, sometimes two, to fade away. The repair tech told us the problem would go away after a few months or years.

It's been easily ten years since the discussion with the repair tech. I was visiting my mom a few months ago and noticed that the TV still had the color smears, albeit about half the size I remember and they faded away in less than thirty minutes. The smears have never noticeably affected the TV while it was powered on, only after it was turned off.

Then I realized that of all the tubes I've ever come across in the wild, I have never seen this problem exhibited on any other tube.

So was the repair tech right? Is this really due to "hyper-active" phosphors, or was I fed a line of ---That which is odiferous and causeth plants to grow--- and we've had a defective screen all these years?

[Pac-Fan]

I say smurf poop, but I don't know much about the internal workings of a tube, but in order for there to be any illumination, there has to be power. 

Does it do it with the set completely unplugged from the wall or just when it's "soft powered" off?

Sounds like a faulty chasis feeding it power even with no signal present like by not discharging the tube correctly when powered down and having overpowerd caps still feeding electrons into the tube when turned off.

[qrz]

had been a zenith asc for many years . so, am very curious as to the model # involved.......?
if high voltage remains on the anode (no bleeder res) , there could be enough electrons present to excite the phosphor for a brief period.
 the crt replacement was likely a grade b (rebuilt). the only part changed is the gun ass'y. 
in their set , there may have been a slight defect in the shadow mask or other internal crt mounts - hard to say ...

in most zeniths , the hv discharges to a min level upon pwr down....
 ALWAYS a good idea to manually discharge crts --BINGO! Either that, or I was attempting to say "before" but it was too many letters to type-- handling. no "surprises" 

qrz

[SavannahLion]

Does it do it with the set completely unplugged from the wall or just when it's "soft powered" off?

Regardless.

had been a zenith asc for many years . so, am very curious as to the model # involved.......?

It'll be a while, but I'll check the model next time I visit and take a snap shot of the screen after power down.

[SavannahLion]

Apparently, I don't give my mother enough credit. According to my mother the TV is a 1991 Zenith CC2766S.