Saturday, November 24, 2012

Philips TV 21PT128A/71R: Irregular picture size & shape problem

A TV repair problem that I had recently encountered is with a Philips 21PT128A/71R which exhibited irregular picture size and shape.
TV troubles like this usually indicates a problem with filter capacitors so I visually checked electrolytic capacitors on the main PCB.
One electrolytic capacitor on board location C2453 looked suspicious with its slightly bulging top. Checking the part using a capacitance meter, it read 3 microfarad instead of its indicated value of 680uF/35V.
 I replaced the capacitor with an available part on hand with a value of 1000uF/50V which restored normal size and shape to the picture.
The capacitor is a filter for the +25V scan-derived supply from the flyback transformer.

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