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Originally Posted by Whirled One
One thing I have noticed, though, is that this set has about the most pronounced "turn-off spot" I've ever seen on any TV. When you switch the set off, you get a *bright*, tightly-focused pin-point of light that takes several seconds to even *start* to defocus or dim out, and takes perhaps 30 seconds to fully disappear. You can even see a visible "halo" around the spot that looks sort of like when you have the intensity control turned up too high on an oscilloscope. I don't see any actual phosphor burn-in, but this can't possibly be good for the CRT... Is there a typical cause/solution for this, say a bleeder resistor in the HV section?
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Don't know about that specific set, but what I've seen done in newer sets that apply the brightness control to grid 1 of the CRT, and video on the cathode, is to tie a big bypass cap between the brightness line on that grid 1 and B+. The cap acquires a charge while the set is on. and when the set is turned off, the B+ quickly collapses to near 0V. The brightness circuit has a fairly high resistance, and that bypass cap slowly bleeds off, forcing grid 1 very negative. To cut off beam current, and no bright spot on the screen. The cathode gets cold and stops emitting before the bypass cap discharges.