Philips 40PFL4908/F7 Squealing Doesn’t Turn On

When plugged in, the TV squealed and wouldn’t turn on. Squealing is a sign of a shorted output on the transformer.

The service manual for this model can be found with a quick google search.

Checking the power supply board, the fuse was not blown and none of the output diodes on the AMP+13V and P-ON+21V lines were shorted. The squealing stopped when the cable from the power supply to the main board was disconnected. Measuring the resistance of the P-ON+21V line, it was 8 ohms indicating a short on the main board.

The schematic shows the P-ON+21V is input to five regulators on the main board that have decoupling capacitors for each one. The 4.7uF 0805 ones could potentially short. You will need to remove C3943, C3645, C3616, C3674 and C3625 to determine which one is shorted. It is advised to replace all of them. Digikey part would be 1276-6722-1-ND (4.7uF 35V X5R 0805)

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