TNPA4250 Board Repair

[tom66]

Re: TNPA4250 Board Repair

It should be sufficient to do a quick test yes.
You should use 10X probe, set scope to 10X mode and 50V/div, maximum memory (56Mpt), timebase 20ms/div. Centre trace and capture one shot.

[canadaboy25]

Re: TNPA4250 Board Repair

Well I hooked everything back up and put my scope on the test point. When I turned the TV on the wave on the scope was completely flat but rising slowly. Ater a second or two the TV started making the faint humming noise that you can hear if you put your ear close to the back of any other TV or monitor so I don't think that sound is out of the ordinary. As soon as it started humming the scope showed a signal which I have attached. The signal stayed up for about half a second but then the TV switched off and gave me the blinks.

If I unplug the data cable from the SC board the TV will stay powered up just like it always has. When it is running the signal from that test point is exactly the same as the signal I got from the half second the TV was runing with the cable pluged in. So it would seem that the data cable isn't having any effect on the signal.

The three files I have attached are all of the save waveform but I have just zoomed in more on each one.

[canadaboy25]

Re: TNPA4250 Board Repair

I there's something I did wrong I can repeat it because I'm not very experienced with scoping.

[tom66]

Re: TNPA4250 Board Repair

Is that with 10X probe, and scope at 10X? If so, you have no VSUS portion of the wave. And there is also no negative portion (-VAD or -VSET2.) This would indicate perhaps low VSUS, or a problem with the driver circuit for that portion. (IGBTs, gate driver, etc.) Can you try probing the gate of one of the HIGH side VSUS IGBTs (the drain should connect to the VSUS) and see if there is any waveform present.

For record, should look vaguely like in this post:
https://www.badcaps.net/forum/showpo...6&postcount=15

Note that's from a 2008 panel which is pretty similar to the 2007 panel. Drive waveform is slightly simpler.

[canadaboy25]

Re: TNPA4250 Board Repair

Sorry for the slow reply.

I performed the tests again and it ended up that in my previous tests the scope was set to 1x instead of 10x due to me unplugging and moving it which wiped my settings. I have a 10:1 probe which is, acording to the manual, a 10x probe.

With that data cable plugged in I only get a tiny signal for a split second, simmilar to the waveform I previously posted. With the data cable unplugged I get the attached waveform. Each image is zoomed in more than the previous.

My apologies for the faulty measurements.

[canadaboy25]

Re: TNPA4250 Board Repair

Both the SU and SD boards are connected while I was testing if that matters.

[tom66]

Re: TNPA4250 Board Repair

So just to check, that is the SUS output, to SU/SD boards? Looks ok for sus but there's no -VAD or VSET ramp. Have you got -VAD/VSET voltages at relevant testpoints? Also, your sus looks a little low - about 150V - what's Vsus rated for this panel?

[canadaboy25]

Re: TNPA4250 Board Repair

So just to check, that is the SUS output, to SU/SD boards? Looks ok for sus but there's no -VAD or VSET ramp. Have you got -VAD/VSET voltages at relevant testpoints? Also, your sus looks a little low - about 150V - what's Vsus rated for this panel?

All of the waveforms that I have tested came from the SC output, or TPSC1, on the SC board.

I have attached the correct voltages from the manual and a picture of the voltage label on my panel.

The -VAD at TPVAD tested -139.1 volts. VSET at TPVSET tested 320.4 volts. I tested the VSUS at TPVSUS on the SC board and it read 212.8 volts which is basically spot on with the label for the voltages on the panel.

[canadaboy25]

Re: TNPA4250 Board Repair

VSCN still only has around 9 volts

[tom66]

Re: TNPA4250 Board Repair

OK, does vscn rise when buffers are removed?

[canadaboy25]

Re: TNPA4250 Board Repair

Unplugging the SU and SD boards has no effect on the voltage. However when the data cable is plugged in the voltage slowly rises and reaches around 43 volts by time the TV shuts off.

[canadaboy25]

Re: TNPA4250 Board Repair

Would there be any way to trick the TV into staying on long enough to test the voltage?

[canadaboy25]

Re: TNPA4250 Board Repair

Any Ideas?

[tw2005]

Re: TNPA4250 Board Repair

TPVAD -139.1 volts. -140V ± 1V

TPVSET 320.4 volts 365V ± 7V Vset SOS DET 289V or less so this should not be the trip

TPVSUS 212.8 volts matches panel

VSCN around 9 volts Vad + 148V ±1V = -139.1 + 148 = 8.9 volts, manual states "When Vad=-140V, Voltage of Vscn is 8V ±1V."

vad,vset,vscn,vfo, 5v(sc1), 5v(sc3) all form part of sc_sos2 or 7 blink.

hard to work out and understand but that's what i see at the moment looking atthe training guide of a pz700 and this pz77U manual

[tom66]

Re: TNPA4250 Board Repair

It's potentially risky, but you could try shorting the SOS7 test point to ground. This would disable the error feedback. But if something goes wrong, it could be fatal to the board, so be careful if you do this.

[tw2005]

Re: TNPA4250 Board Repair

It's potentially risky, but you could try shorting the SOS7 test point to ground. This would disable the error feedback. But if something goes wrong, it could be fatal to the board, so be careful if you do this.

yeah, but where there's , the problem will be near

honestly if trying this, solder one end on the sos7 tp and earth the other holding it by hand at least you can release it and tv will shutdown.

tried this 3 times on a hunce. twice it worked and helped, third time, ah, burnt the board and vaporised a track. stupid thing was i had the wire all i needed to do was release it for the shutdown, instead i starting screaming for someone to cut the power.

A dumb moment of panic which i laugh at .

[tw2005]

Re: TNPA4250 Board Repair

The other thing is maybe find the diodes these signals pass through for each section they monitor and find the one which has a high on the anode side since all the cathodes are tied. may be able to at least find the section producing the high for shutdown and trace it??

[Neelix]

Re: TNPA4250 Board Repair

yeah, but where there's , the problem will be near

honestly if trying this, solder one end on the sos7 tp and earth the other holding it by hand at least you can release it and tv will shutdown.

tried this 3 times on a hunce. twice it worked and helped, third time, ah, burnt the board and vaporised a track. stupid thing was i had the wire all i needed to do was release it for the shutdown, instead i starting screaming for someone to cut the power.

A dumb moment of panic which i laugh at .

Reminds me of the time I was working on a PA system and the amplifer circuit caught fire. There was flames coming from the board. I was shouting for somebody to bring the fire extinguisher, when all I really had to do was switch the power off at the electrical socket. As you can imagine, the board was toasted

[canadaboy25]

Re: TNPA4250 Board Repair

TPVAD -139.1 volts. -140V ± 1V

TPVSET 320.4 volts 365V ± 7V Vset SOS DET 289V or less so this should not be the trip

TPVSUS 212.8 volts matches panel

VSCN around 9 volts Vad + 148V ±1V = -139.1 + 148 = 8.9 volts, manual states "When Vad=-140V, Voltage of Vscn is 8V ±1V."

vad,vset,vscn,vfo, 5v(sc1), 5v(sc3) all form part of sc_sos2 or 7 blink.

hard to work out and understand but that's what i see at the moment looking atthe training guide of a pz700 and this pz77U manual

Ahh yes I suppose your right. I read that but I really didn't think about it too much. So it would seem that all of my voltages are correct..

[canadaboy25]

Re: TNPA4250 Board Repair

It's potentially risky, but you could try shorting the SOS7 test point to ground. This would disable the error feedback. But if something goes wrong, it could be fatal to the board, so be careful if you do this.

Ill try this out. The worst that can happen is I wreck a wrecked board!