Bypass disable SOS - Panasonic

[itelite]

I have a purely evil TH-50PX60U that is giving 6 blinks.

I have already replaced SC and SS. I have tried removing SD and SU one by one with no change. Just 6 blinks.

Occasionally the tv will turn on and run for about 10 minutes before shutting down with 6 blinks. I have no explanation for this.

I would love to bypass SOS6 and hopefully stop the shutdown. Even if something explodes, at least it will give an indication of where the problem is.

The SOS6 line will go to 2.7v before the tv shuts down and then it of course goes to zero.

I have cut the SOS6 line (8 blinks), tried grounding (8 blinks), tried feeding 2.7v, 3.3v , and 5v into it. All of these get 6 blinks.

Can someone explain how these SOS lines work, and if it is possible to fake the signal required to tell everything to keep running.

[freakaftr8]

Re: Bypass disable SOS - Panasonic

You may be able to fake the signal by monitoring pin 3 of Ic 9003 on D board as the TV is working and keep watching the voltage when the tv shuts down I believe there should be 5v.

If TV shuts down and voltage goes low on that pin you may be able to inject 5 V into that can to keep it alive. There is a reason for this to be happening and it may be caused by a shorted COF on the C buffer

[itelite]

Re: Bypass disable SOS - Panasonic

appreciate it. i will give a try.

for what it's worth, when it is running, there is no visible indication anything being wrong.

I also unplugged the FFC cables from the d board as a troubleshooting step, with no change from the 6 blinks.

[freakaftr8]

Re: Bypass disable SOS - Panasonic

Ok. The D board sends the 5v through the SC to the C buffers and back to the D board. Stupid but that's how it works.

[tom66]

Re: Bypass disable SOS - Panasonic

SOS6 is generated by the VMID / ER voltage balance.
I would check the VMID voltage on the poly caps in the energy recovery circuit
Follow the schematic and it'll show you where SOS6 is generated...

[itelite]

Re: Bypass disable SOS - Panasonic

Excellent. Will check those caps, as well as get some voltage measurements form the circuit.

I spent most of yesterday in the schematic to no avail ha.

For the record, issue is exactly the same across 2 different SC boards, and 2 different SS boards. So that is why i haven't dug too deep into the circuits on those boards.

I suppose one of the main things i am wondering is what exactly does a valid SOS signal look like? This is just going high(?) 2.7v until the set powers off, but when disconnected or held low a then get a 8 blink code. That is to say, when looking on an a scope i dont see any discernible signaling pattern, but i dont know if i really should.

[R_J]

Re: Bypass disable SOS - Panasonic

If you have the same problem with two different SC & SS boards, It could be the D board that is faulty, There is a zener diode (D9019) that could be intermitint, or C9051 Try lifting them and see if the fault is still there.
Check the voltage on R9110

[itelite]

Re: Bypass disable SOS - Panasonic

Wondering if the schematic i have is not correct. Board is TNPA3820 AC 1 d

The numbers on the board do not match the schematic numbers at all. For instance IC9003 is shown as existing on the schematic. Where as i have things like IC300 and IC400 on this board.

Matches perfect to the board layout of the D board in the board layout image in the service manual.

[R_J]

Re: Bypass disable SOS - Panasonic

I believe it is ic003 on the board, drop the `9' The zener diode D9019 would be D019

[itelite]

Re: Bypass disable SOS - Panasonic

Yes, dropping the 9 makes sense.

lifting the ZD and cap made no difference. Capacitor is not shorted. r9110 reads 100 ohm as expected. R9172 read 39k as expected