Panasonic TC-P50G25 SC board TNPA5081AF shorting again after repair

[Yanleb]

Hi all,

After repairing my TNPA5081AF, it shorts out immediately after powering it.

I traced down the problem to the SOT23-5 Inverter IC773 (marked HA on its case, and IC16773 on the schematic). The chip receives a supply voltage of 5 volts but it receives 16 volts on its input. This is what I measure on the board, and this is also what I see on the schematic.

I think that I found the data sheet of the IC773 chip. It should be a TC7SH14F. Its max input voltage is 7 volts. This is not a surprise that the chip will short out when it receives 16 volts on its input.

Did you already had problems with this chip? What would be the correct replacement?

Thanks.

[lotas]

Yes, everything is correct, this is C0JBAB000715 IC(16)773 "TC7SH14F"

[Yanleb]

Thank you for confirming the part number. But can you explain why it is shorting out immediately? I just don't understand why there's a transistor to pull the input to 16V_F while the input is only rated at 7 volts.

The schematic matches the board. And effectively I measure 5 volts at pin 5 VCC and 16 volts at pin 2 IN_A. Does it mean that this is a design flaw? Or that Q16702 is not supposed to be turned on?

Maybe I'm wrong to assume that 16V_F is 16 volts in reference to VAD. Can someone confirm?

Another question, can someone explain me why the base of Q16701 is connected to ground?

[Biruslapio]

any _F = floating ground, which is a ground specific to plasma sustain voltages in the tv, it's the same as probing the screws that go into between SC and buffer boards.

[kasfamily]

https://www.badcaps.net/forum/troubl...-rebuild/page8