Panasonic TC-P42ST50B - 7 blinks after some time

[tom66]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

BD8658Z, yeah it's got a thermal pad. Can't find a datasheet or even spare parts. Part number indicates Rohm.

Might not be this chip - could be adjacent parts. It probably monitors: VF15V, VF5V (its output), and some kind of pre-unregulated rail, possibly 20V or so, which is used to generate VF15V. It may also monitor the HIZ signal from the A board, but this might just be an enable (makes sense because the output dies straight away after SOS7).

[tw2005]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

Well, Hopefully you'll work it out. probably a ROHM product but unlikely you'll find much on it bit like those driver ICs

[tw2005]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

4 pictures for you. Looking at this , wondering either ic725 or that optocoupler pc480 which grounds out the 5V high for shutdown( under normal condtions) and driven by ic725

[tom66]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

Very useful. Thanks! Where do you get these documents? I can't find them anywhere..

"main_stop0" is not the final SOS7 apparently, there are other "post-causes" like Vad/Vscn overvoltage that can cause a shutdown. Will need to verify these. Shouldn't be too hard to figure out the exact source - question is will parts be available?

I ordered the £16 SN board, but it would be nice to have two SN boards.

Testing TPSOS7 shows that it is definitely the final fault trigger. It goes HIGH, which causes the SUS outputs to collapse, 250ms later the A board cuts the show off and we get 7 blinks.

What's interesting is how quickly it cuts off, I think Panasonic have learned a lesson from the expensive repairs on '30 series which could kill buffer ICs. This operation should kill the power to every high-voltage component nearly immediately. Then there's only the AC-coupling across the panel itself from the SS board, but that shouldn't damage anything.

Trying to figure out how to float my scope so I can do some floating ground tests, but I want to fully isolate it. It will run off 40V DC (just through the mains input, it has a very low input threshold!) but I have no way of easily making that isolated. Could use a bench power supply, but not sure what isolation looks like under high voltage and not really willing to blow one of those up to find out.

[tom66]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

Yeah, deffo main_stop0 causing the fault as it does exactly the same thing as sos7. Goes high and immediately drive outputs collapse.

[tom66]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

OK, so I was brave (or stupid - I'll leave it up to you) and decided to float my scope. Modified a power lead to remove the earth so I could connect the scope to anything floating. This lets me probe the floating ground side with the scope.

Doing this, I was able to verify the F20V, F15V and F5V are all fine before and after the fault. F20V is unregulated, about 21V when picture is bright and 17V when it's dark, but this doesn't seem to trip the circuit and the F15V is always steady. The reason it varies is probably because the Vscn/Vad are regulated but not auxillary rails. Nothing wrong with this.

I am now of the belief that the fault is optocoupler PC16480. I have checked the PC pin of the IC16725 and that is LOW throughout the fault. This indicates that it is driving the LED of '480 which should keep main_stop0 low. However, main_stop0 does not stay low, even though the PC pin is still low. So, either the LED or the transistor inside the optocoupler has failed in a way that causes the fault when it gets warm.

I'm now digging around a few boards to see if I have an optocoupler that'll fit, and will see if this fixes it.

If this is the cause of the fault I kinda can forgive Panasonic...this will be one of those "part-per-million" type failures that still occur even with good engineering, and credit to them the circuit is designed in such a way that should the part fail it trips a fault. The actual failure may be something related to a die bond failing under temperature or a damaged LED/phototransistor die.

[tom66]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

Definitely '480. Soldering iron on it causes TV to die almost instantly but not the same for adjacent parts, so it has become heat sensitive somehow. Really odd, but fascinating failure!

[tom66]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

Replaced the opto and reinstalled the board, but for the life of me I cannot get the panel connectors back in and aligned properly - any tips from anyone who has done this? Every time I try, the bottom edge comes out slightly.

[flocko]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

I find that if you leave the board floating on the fixing screws till you get the ribbons lined up it helps, if you can see any of the gold ribbon contacts outside the connectors they are not fully home, when you are happy then crack up fixing screws

[tw2005]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

Nice, yeah at a guess I would have swapped out the opto if I had something handy. can't help with the ribbons , never touched a 50 series. I'm presumuing it's a thin model and the re's no room to get the fingers in? The GT30/VT30 are two models I'd hate to remove the buffers. Bugger it's a SN board

[tom66]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

Bingo, thanks Flocko for the tip, loosening the screws helped get the first one in, then I tightened them progressively as I got up the board. First time was pretty close, only had to adjust three ribbons. Picture is perfect now. Tried a hairdryer on the affected area for a good few minutes and no 7 blinks. Bonus: the opto was free, from a scrap Samsung Y-main board. Doesn't quite fit but it'll do the job!

Thanks everyone. Another TV saved and just in time for the girlfriend to visit tonight .

[flocko]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

just need a little movement on the board to get them to fall into place , nice fix you would have been lucky to find it, without the scope. Have a great time with your girl tonight dont spend it all watching TV, I am sure you can think of better things to get up to

[ReeceyBurger123]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

I'll try monitoring SOS7 and sustain waveforms on the scope, if there's a time delay between one and the other it might clue me into what's going bad where. I'm thinking main board right now - probably BGA solder - ugh. But maybe I can borrow the reflow oven at work.

Told you on whatsapp ages ago that these are known for bga issues mate.

[tom66]

Re: Panasonic TC-P42ST50B - 7 blinks after some time

Told you on whatsapp ages ago that these are known for bga issues mate.

In this case it seems to be fine. I'd expect Panasonic to have got their act together with BGA failures.