Panasonic TC-P50G10B - flashes 7 times, stuck in standby

[tom66]

Nice 50", Freesat HD/Freeview HD, full HD 1080p plasma here for repair. Panasonic G10 series - pretty new stuff! (approx 2 years old I think.)

Picked this one up today with sienoki - anyway, the fault is that it's stuck in standby with the all too common 7 red blinks issue. This is an SC, SU or SD board fault: likely SC, with a shorted FET if I'm lucky. Could be buffers too. I've had 7 blinks before and was able to isolate a FET and get the set to run well.

More info tomorrow when it's disassembled!

edit: it's TX-P50G10B because it's the European version. US version is TC-P50G10.

[allsmith]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Sounds like a nice one! I hope you get it up and running,Im sure you will!

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

OK, got it in the dorm... very big TV.

Think I have isolated SOS7 as coming from the SC board, it fires up briefly to 4V then the TV cuts off with the 7 blinks. Now trying to find a way to disable it temporarily and see if I can get a picture.

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Vad is -40V from GND_BASE; this is good.
Vscn is -185V from GND_BASE, also good.

Disabled SOS7 and then it gives me SOS6. So not erroneously detecting a fault, there's definitely something up on the SC.

SOS7 definitely spikes up to 4V on my scope for 200ms.

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Bingo... the specific fault is the VSCN. There's nothing wrong with it, but it is detecting a fault, probably undervoltage lockout. Collector of Q876 and R752 is firing the pulse into the OR-diode, which sends SOS7 to the A-board. Need to figure out why though.

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

I'm getting a spike on SOS7 that's not being generated by the SC, I think. It's not on either of the anodes of the diode OR-logic. So it's coming from somewhere else. There is a little spike but it occurs on shut down and start up only, so I think that's OK. I may be wrong.

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

IC561 is generating the shutdown pulse. It's not happy with something... Need to figure out why but it's definitely coming from there, must have missed it in the schematic.

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

MAIN_STOP0 is going high, which is buffered by the IC561; this then OR's the fault onto SOS7. Need to find out why MAIN_STOP0 is firing. Possibly a bad FET somewhere; maybe not firing as it should. Page 74 has the main stop detection circuit. Time to look at that.

[tw2005]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

did you find any shorted components?

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Not yet. There might be some tiny SMD diode shorted or open or something similar out of tolerance; but all big power FETs/IGBTs/diodes test OK.

SOS7 with the MAIN_STOP0 firing could be caused by SCRN_PROT, low isolated 5V or CHA protect (whatever that is...)

Also noticed this TV has ethernet. Smart TV features??

[tw2005]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Just had a quick look at the schematic. Design looks similar to the P42X14 I isolated the sos7 with a low VAD and adjusting the pot made no difference for VAD.Pot was good.
MIP9L02 was the ic for VAD on mine too.

What did you do to isolate sos7?

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Checked around all the SOS7 test points to isolate it. VAD and VSCN are good and adjustable. VSUS was set too low, so I adjusted it to the panel sticker (206V; was 199V.) Someone has been in here before me, there are some screws missing - I hope nothing else has been messed with.

Have now found the 16V line only hits about 3.5V or so before SOS7 falls over; some how it's being held down. It's provided by a little plug in hybrid module, which will be a bugger to find a replacement for... argh.

The 16V provides power to the 5V sub reg, which gives some of the SOS7 protection ckt power to signal CHA, SCRN_PRO, 5V UVP or OVP (not sure), and 16V OVP (possibly also UVP - it's a bit difficult to understand - I may end up simulating the circuit in LTspice.)

So it definitely does a lot of things for one error code! I guess Panasonic just expect a board swap.

[tw2005]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Geez mate ease up on all the techno stuff, I'm getting a headache with all the abbreviations.. Are you studying engineering or something?
I misunderstood you, I took isolate to mean disabled. How did you disable sos7?

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

MEng ElecEng undergrad , at the University of Leeds... arrived about a week ago.

The abbreviations I've used are the ones Panasonic used. I have no idea what most of them stand for except UVP = under-voltage protect, OVP = over-voltage protect, ckt = circuit.

Disabling SOS7 can be done by shorting the test pad to ground. I used the 10A range on my meter. SOS7 was zeroed, but then SOS6 triggers because there's another fault... I'll guess the low 16V is part of that as it provides power for a few other things. Isolating it means trying to locate the specific error causing the SOS7 shut down.

[tw2005]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

When I was young I started Elec Eng, got lazy and quit. Wish i followed it through. Now just a tech in a place that justs board swaps and no deeper level stuff.

Still interested in how you removed the SOS7.

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Disabling SOS7 can be done by shorting the test pad to ground. I used the 10A range on my meter. SOS7 was zeroed, but then SOS6 triggers because there's another fault... I'll guess the low 16V is part of that as it provides power for a few other things.

[tw2005]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Disabling SOS7 can be done by shorting the test pad to ground. I used the 10A range on my meter. SOS7 was zeroed, but then SOS6 triggers because there's another fault... I'll guess the low 16V is part of that as it provides power for a few other things.

Well that was easy compared to what I did. I went invasive and cut a track + removed a tiny double diode(don't know what to call it)

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Well that was easy compared to what I did. I went invasive and cut a track + removed a tiny double diode(don't know what to call it)

Double diode is the term. All the SOS7 has 4.7k resistors in series, I checked, it limits current due to short circuit so is OK.

[tw2005]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Vad is -40V from GND_BASE; this is good.
Vscn is -185V from GND_BASE, also good.

Disabled SOS7 and then it gives me SOS6. So not erroneously detecting a fault, there's definitely something up on the SC.

SOS7 definitely spikes up to 4V on my scope for 200ms.

Did you mean VAD = -185 & Vscn = -40V?

[tom66]

Re: Panasonic TC-P50G10B - flashes 7 times, stuck in standby

Measured relative to the case of the TV. But in reality, VSCN is relative to VAD... around 145V. It's pretty complicated to drive a plasma panel! It amazes me the newer Samsung plasmas have got it down to just 8 devices on the Y-main and three on the X-main. There's nothing to it on them. They probably won't last too long though; maybe just getting out of warranty.