We had a newish 2004 Panasonic TC21PM50A (GP-3 chassis) come in under warranty with the fault description "dead". Apart from the dealer receipt, no other information was supplied.

It was soon apparent that the switchmode power supply was more or less working and supplying 140V at the cathode of D854 (TPA10).

But the 14V rail was running at 38V from the cathode of D855 (at standby it should be only 7.5V). This had destroyed the smoothing electros C862, C880 and C2380, all of which are rated at 16V.

This also meant there was over 100V across Q850 and R850 (47Ω). These were replaced but this didn’t account for why the low voltage rail was so high.

Even though the 140V was correct, I felt that somehow the feedback wasn’t quite right and so IC802, the 140V optocoupler IC driver was changed, as was IC851, the switchable 8V and 5V IC regulator.

But nothing significant happened until D860, the PC123 optocoupler, was found to be leaky on both sides. Replacing this brought the voltage down to 14V (7.5V standby).

However, the 8V line TPA8 to the microprocessor (IC601) on pin 39 was still 0V and this was due to a short inside the IC itself. Replacing the IC fixed this and the set came on.

There was now sound but no picture. There was a white raster with a black bar beneath it, one-third of the way up the screen. Replacing the EEPROM (IC1103) finally resolved this last issue.

Methinks this was a bit more than a warranty claim – I suspect lightning had a lot to do with it!

Items Covered This Month Panasonic TC21PM50A (GP-3 chassis LG CF-25H30N (MC-74A chassis) LG LCD RT-13LA60 NEC MT840G Yamaha RX360 amplifier Onkyo TXD5676 amplifier Blaupunkt CS82-103VT FM 542.60 chassis Panasonic Tau Giga TX80-P300A (Euro 7A chassis) Sony KV-L34SN11 (G3F chassis) Philips 29PT8419/79R (EM1L chassis)