TNPA4250 Board Repair

[canadaboy25]

Re: TNPA4250 Board Repair

Well I soldered a wire to SOS7 and shorted it to ground but the TV just shut off sooner that it did before. I tested the voltage between SOS7 and ground and there was around 2.8 volts if that means anything...

[tom66]

Re: TNPA4250 Board Repair

If you remove that, is it all as before?

[canadaboy25]

Re: TNPA4250 Board Repair

Yes it's exactly the same as before.

[canadaboy25]

Re: TNPA4250 Board Repair

The little power indicator on the SC board is off when the wire is shorted.

[tom66]

Re: TNPA4250 Board Repair

That's odd, I'm wondering if the control board expects it to go high then low (it does on a working board.) Perhaps try grounding it when it powers on but just before it cuts out.

The light indicates the ER circuit is operating, by the way, which generally means the panel is being sustained (made to light up)

[canadaboy25]

Re: TNPA4250 Board Repair

Well I've been poking around and found the problem, I didn't have the power plugged into the SC board... my bad (no wonder the indicator light wasn't lighting up)

I plugged the board in and shorted the test point to ground and the TV stayed on.

Am I supposed to retest the SC output with my oscilloscope now?

[tw2005]

Re: TNPA4250 Board Repair

Well I've been poking around and found the problem, I didn't have the power plugged into the SC board... my bad (no wonder the indicator light wasn't lighting up)

I plugged the board in and shorted the test point to ground and the TV stayed on.

Am I supposed to retest the SC output with my oscilloscope now?

For me, remove the shorted sos7, obviously with no sc2 connected it would trip 7, retest if stays on and picture good I'd leave it at that provided no other adjustments have been made unless you want to double check what the voltages are set too but if you never changed them then i would expect it to be good

[tom66]

Re: TNPA4250 Board Repair

Yes, test SC output, any picture on screen, even if poor?

[canadaboy25]

Re: TNPA4250 Board Repair

I will test the output today.

From what I can tell there was nothing on the screen at all.

[canadaboy25]

Re: TNPA4250 Board Repair

Well while I had the panel lifted looking at the screen I heard a snap like a high voltage spark and the TV shut off.

Now it won't stay on even with the test point shorted.

[tom66]

Re: TNPA4250 Board Repair

I think that's the risk you get when you disable an error detect, something could go pop.

[canadaboy25]

Re: TNPA4250 Board Repair

The board does still stay on when I unplug the data cable so it there any way that I can still test it?

I had the ground lead of my oscilloscope connected to the heatsink on the SC board and the tip of the probe may have (I'm not completely sure) made contact with one of the via's on the SU board. The reason I suspect this is because there was a slight blackish soot mark (like the one made from a large spark) near the via (the probe was also close to here).

I don't think that the SU board is the problem because the symptoms do not change when it is removed.

I also don't think that something just went pop from being overloaded for too long because I had previously had the board powered up for much longer with no issues that the time when it got zapped.

Stupid mistake on my part but I hope that there is still something that I can do.

[canadaboy25]

Re: TNPA4250 Board Repair

It may also be worth noting that the TV now blinks 5 times when it shuts off.

[canadaboy25]

Re: TNPA4250 Board Repair

I have followed the troubleshooting guide on your website and I have narrowed the fault down to the 5v supply on the power board. (It said replace the P board but I'm not about to do that)

So basically i ruined the 5v rail. How would I go about testing the power board?

[canadaboy25]

Re: TNPA4250 Board Repair

Sorry I was wrong. I went and took the power board off and took off a bunch of parts and tested them and everything was testing fine. I eventually put the board back in and tried it again and it turns out I counted the blinks wrong.

It is blinking 6 times which means SC energy recovery circuit. I have no idea what that is but it is still on the SC board.

[tom66]

Re: TNPA4250 Board Repair

Does the green LED ever glow?

[canadaboy25]

Re: TNPA4250 Board Repair

Yes, the green indicator on the board lights up when I turn it on.

[tom66]

Re: TNPA4250 Board Repair

Does it go out before the relay clicks and you get SOS6?

[canadaboy25]

Re: TNPA4250 Board Repair

The green light stays on after it flashes. It stays on even after I unplug the TV and only shuts off once all the power stored up in the capacitors and stuff drains out.

[canadaboy25]

Re: TNPA4250 Board Repair

The green indicator light is lit up on the board on the other side of the TV too.