My Panasonic CT-20S12S keeps slowly getting brighter and brighter, and I keep having to take off the back and turn down the SCREEN control.

What's going on here?

  • 3
    Same as with your other question, main transformer faulty.
    – Janka
    Jan 21, 2018 at 19:44
  • 4
    @Janka That should be an answer, not a comment. Please post it as such so the question can be marked as answered. (Also, this question is useful in its own right, despite having the same answer, because it's a different question.)
    – wizzwizz4
    Jan 21, 2018 at 20:05
  • 1
    @Janka As for my other question, I should have been more specific. It's not large bowing, just small imperfections with edges (just normal geometry problems).
    – user7645
    Jan 21, 2018 at 20:13
  • the more dense the image is warped the brighter it gets as the electron ray spends more time in such region then it should. That is geometry problem. Also wrong darkening timing of the Vertical triangular generator can be a cause of this. If the brightness is changing on whole image that usually signal problem with high voltage multiplier/trafo but usually with fault like that the image goes darker instead. Usual solution is to add few screws to the transformer secondary coil (but in your case remove which I am not convinced is the case).
    – Spektre
    Jan 22, 2018 at 8:33

1 Answer 1


It sound like to me a power supply issue. You mentioned about imperfections on the edges. I had a very similar issue with a CRT computer screen. In my case it was a filter capacitor and a full wave bridge rectifier that went bad. 2 diodes were fried by a power surge and some AC was making it to the filter capacitor. When both were changed the screen was good as new.

It started as small ripple effects on the edges with changes in brightness which eventually became more like light and dark horizontal bars. When servicing most electronics check power supplies as they feed all the circuits .

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