red mark in center of 95cm tv

Old 04-10-00, 03:29 PM
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I have a 6 year 95cm grundig tv (model:ST95-775/9 PIP/TOP),about a year ago it was repaired due to loss of the picture,with an upgraded part from grundig. Almost immediatly we noticed that when the tv was switched off,a bright white dot appeared in the center of the screen for a second.When the tv was on, we noticed a redmark in the center of the screen,this has now progressed to a thin red line approx.1/4inch long embeded in the screen, also the tv switches itself off sometimes.Can anyone tell us what the cause could be, thanks
Old 04-10-00, 05:03 PM
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Yah, I can define it for you. You have a deflection yoke on the neck of your picture tube that was geared for 100 volts 50 cycles. Running the system at 120 volts 60 cycles, you have have a "yoke flash" .
Most technicians will tell you that this doesn't exist. But, I have been working on the sets since 1960 and have seen it happen several times. Always the problem occurs from the units from Europe (Grundig)
A defelection yoke on the neck of a picture tube is "inductive" by nature and a change in frequency of the line voltage causes a reactive quality that causes the yoke to change characteristics. Then what you get is a longer duration scan in the center of the screen which results in a burn of the phospher.

As I said, the younger technicians will deny this happens. But the older guys who have been working on these sets for twenty or thirty years will remember those "yoke flashes".

Is there a fix? No. At least none that are equitable to the owner of the set. There is no replacement part available to repair it that I am aware of. It is a problem that results between two cultures, two systems of electrical standards, etc.

What you have is a burn in your phospher on the picture tube screen. Nothing I know of will repair it. Sorry. That's as good as it gets.

Others are offered the opportunity to respond and, perhaps, offer an alternative.


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