I recently obtained an Philips 20PT1553-00 TV set. The picture is
usually relatively dark. I have to turn the brightness and the contrast
fully up to obtain a viewable picture. The effect of the
brightness-control is nearly non-existent. Sometimes (very seldom) the
whole picture brightens up and the brightness-control works. This lasts
usually bwetween 5 and 30 seconds. After that, the picture turns dark
again.

Has anybody experienced something like this before? Does anybody know
what could be wrong?

Thanks

Eberhard