Panasonic TC-P50GT50, Won't turn on.

[JayArr_BC]

Hi All

It's officially Panasonic week here at JRElectronics LOL I've received five in a row, one repaired and four left. I don't normally even repair TVs but it's bad PR to turn away the work, I'm the last shop left in town. Besides, I like Panasonic and I like plasmas, I wish more people would buy higher quality stuff and have it repaired when it breaks.

This one won't turn on, no lights at all and no flash of screen.

Measuring 5V STBY it's only 4.5V so I moved up to the PFC circuit and it's only 169V. Those PFC caps are rated at 450V I would have thought I'd get 385-400V there. Does anyone agree?

Would it be a good guess that if I fixed the PFC so that it's 400V I'd get 5V back on the STBY and the set would work?

Any help appreciated, I've downloaded the manual but Panasonic used a Hitachi power supply "P" board in this one so there is no schematic, just a block diagram.

JayArr

[R_J]

Re: Panasonic TC-P50GT50, Won't turn on.

The standby is usually seperate and does not depend on the pfc circuit, The pfc circuit is turned on when the tv gets turned on.
4.5 volts is not that far off the 5 volts and liklely not the cause of the problem.

[JayArr_BC]

Re: Panasonic TC-P50GT50, Won't turn on.

Bummer. The STBY circuit is fed straight off the PFC circuits on this one and the block diagram indicates the PFC works in stby so long as it detects AC. I was hoping it would be that easy.

I've also noticed that I don't get a relay click. There's a 15 ohn 5W resistor accross the relay contacts for stby but it's not clicking, I tested the relay itself and it works and the contacts only have .02 ohms resistance so I'm wondering why it's not turning on.

[R_J]

Re: Panasonic TC-P50GT50, Won't turn on.

The standby circuit usually is fed by 160 volts, There is no need to run the pfc circuit to operate the standby, it would be a waste of energy.
The a/c runs through the resistor because in standby only a small current is needed, when the tv is powered on, the relay shorts the resistor so more current can be supplied when the pfc and Vs,Va +15v etc are turned on.
You need to see if there is a power on signal from the main board when the power button is pressed.
My guess on this tv would be a bad main board.
Check P6
Pin6= EV5V (standby)
Pin1= Panel_main_on (turns power supply on)

[JayArr_BC]

Re: Panasonic TC-P50GT50, Won't turn on.

Thanks R_J

I had a chance to get back at this set again last night. Your instinct was correct, there is no signal from the main board when I press the power button.

I followed the stby power in from the power supply and it goes to IC5000 which is an AN34044AA IC that has several regulated outputs. When I follow the Panel_mains_on signal from pin 1 it leads back to the large BGA IC, IC8000 which would be the main microprocessor.

So my guess is that IC5000 is not working and so IC8000 has no supply voltage and the baord is dead. I've found a supplier in CHina and purchased a couple of the AN340044AA ICs and I'll give it a try when they come in. There are listings on eBay for repair services so there is definitely a way to repair these, I just have to find it.

BTW, my other set (TC-55CX650U) that is flashing only one blink uses a similar AN34043AA IC on it's A board so I'm ordering two of them as well, it would be nice to find that these A boards are easily repairable with multi-output low droput regulators selling for $2.

JayArr