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)

Update – I got a second one in with no standby light but no squealing. P-ON+21V only measured just above 1V but went up to around 12V with the main board disconnected. The supplies run at half voltage in standby mode. This pulled down voltage is an indication of a short on the main board. C3616 on the 3.3V regulator, IC3603) was what I replaced before and again this was shorted. You may likely get away with just replacing just this capacitor. The other 4.7uF caps are C3625 (IC3607 5V), C3943 (IC3901 12V), C3645 (IC3604 1.14V) and C3674 (IC3602 1.5V).

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