Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

[raftman]

Greetings! I picked up this tv with a 14-blink no power condition. After some research I decided to replace the SS board and rework the SN board, using the repair kit from ShopJimmy).

Now the TV powers on (good), both green LEDs are on for both the SN and SS boards (yay), but the image quality isn't right (bad). Picture attached. You'll see colored, snowy pixels. I ran the self test mode and everything it reported was 'OK'. I can run any test patterns and access the service mode if that will help. I had to adjust many parameters - like R-cut, B-cut, G-cut, R-drv, B-drv, G-drv, etc because at factory values the blue pop-up windows were completely washed out white. At least now I can read the text for testing purposes.

I've seen a few other threads having similar issues with Panasonic TV's and people suggested replacing and checking different components. I am electrically competent but don't have experience repairing TVs. I'm sure eventually I'll find shorts and replace the right component(s), but why reinvent the wheel when someone here probably knows right away where to look.

The shopjimmy SN repair kit included transistors Q401, Q402, Q421, Q422, D401, D421, and 4 resistors that sit next to the transistors. All have been replaced. I reworked a second time to be sure these components were down correctly.

What I'm asking for help with here:
1) What voltages should I check?
2) Which components should I check?
3) Why, in the service manual schematics, are components labeled Q16401 when on the PCB they are labeled Q401? What's with the extra 16?
4) I've seen reference to checking/replacing Q441, Q531, IC502, D481. Suggestions for sourcing these parts if I decide to replace?

Thanks - getting this tv over the bump to 1080p glory would make me most appreciative!

[tw2005]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

Greetings! I picked up this tv with a 14-blink no power condition. After some research I decided to replace the SS board and rework the SN board, using the repair kit from ShopJimmy).

Now the TV powers on (good), both green LEDs are on for both the SN and SS boards (yay), but the image quality isn't right (bad). Picture attached. You'll see colored, snowy pixels. I ran the self test mode and everything it reported was 'OK'. I can run any test patterns and access the service mode if that will help. I had to adjust many parameters - like R-cut, B-cut, G-cut, R-drv, B-drv, G-drv, etc because at factory values the blue pop-up windows were completely washed out white. At least now I can read the text for testing purposes.

I've seen a few other threads having similar issues with Panasonic TV's and people suggested replacing and checking different components. I am electrically competent but don't have experience repairing TVs. I'm sure eventually I'll find shorts and replace the right component(s), but why reinvent the wheel when someone here probably knows right away where to look.

The shopjimmy SN repair kit included transistors Q401, Q402, Q421, Q422, D401, D421, and 4 resistors that sit next to the transistors. All have been replaced. I reworked a second time to be sure these components were down correctly.

What I'm asking for help with here:
1) What voltages should I check?
2) Which components should I check?
3) Why, in the service manual schematics, are components labeled Q16401 when on the PCB they are labeled Q401? What's with the extra 16?
4) I've seen reference to checking/replacing Q441, Q531, IC502, D481. Suggestions for sourcing these parts if I decide to replace?

Thanks - getting this tv over the bump to 1080p glory would make me most appreciative!

1) What voltages should I check? Vsus (across p2 or sn2)
2) Which components should I check? I don't know, was the SS bad or not?
3) Why, in the service manual schematics, are components labeled Q16401 when on the PCB they are labeled Q401? What's with the extra 16? 16 is the board identifier, look at it , it will have CRn 16000 on it somewhere
4) I've seen reference to checking/replacing Q441, Q531, IC502, D481. Suggestions for sourcing these parts if I decide to replace? ebay, utsource

[raftman]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

1) What voltages should I check? Vsus (across p2 or sn2)
ok - can do tomorrow.

2) Which components should I check? I don't know, was the SS bad or not?
SS board currently in TV is fresh from SJ. The old SS board did not illuminate the green LED. Per another post somewhere and the service manual I replaced both SN (only replaced components listed in OP) and SS simultaneously. Short answer I don't know if the old SS board is bad or not - I believe it is. I don't want to put it back in because if it is bad, I don't want to re-fry the new components in the SN board.

3) Why, in the service manual schematics, are components labeled Q16401 when on the PCB they are labeled Q401? What's with the extra 16? 16 is the board identifier, look at it , it will have CRn 16000 on it somewhere
Thanks, never seen that before in a BOM

4) I've seen reference to checking/replacing Q441, Q531, IC502, D481. Suggestions for sourcing these parts if I decide to replace? ebay, utsource
Thanks, did not know about utsource. I was hoping digikey would stock, but they do not show anything for those part #'s

[raftman]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

Vsus measures at 213V at P2 with a DC meter. That seems reasonable correct? Some of the components I mentioned I believe control the negative voltage discharging of panel. I can borrow a scope if necessary.

There is a resistor labeled 'tpvad'. The voltage across this resistor, R838, is 188V DC. I think this node is doing something AC since measuring wrt ground gives changing values on dc meter. Schematic says Vad should be 205V +-5, so maybe low if I'm measuring correctly?

I'm tracking down the test point for Vscn, according to the schematic should be 147V.

I'll report that when I find it. If pics of the board will help I'm happy to provide. Thanks.

[tw2005]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

Vsus LO 215V
Vsus HI 220V

Lo & HI are selected via the service menu. Might be worth trying to adjust up on the P board although it's factory set or try selecting HI in the menu, you 'll need the service manual instructions I don't know off the top of my head.

We have seen maldischarge issues with some of these after repair and a couple of volts has made a difference. Just don't know the threads at this stage to have a look.

not sure if this is the issue or not , it's weird display you have for sure. I have not any issues really except with a bad repair job on a SS board and I've only fix one of this series 50U30A and that was simple 4 transistors and no adjustments required

[tw2005]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

188V for VAD is a bit away from the 200-210V quoted

VSCN is shown and will be labelled on the board, usually it's one of those through hole resistors that stick up from the board, should be labelled TPSN1

[raftman]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

I had already tired both VSUS settings in service mode and the high mode did not look much better.

I borrowed a scope and took measurements at TPSN1 and and TPVAD (probe points shown in attached images). On the schematic there are notes by TPSN1: "Reference Voltage Vscn:147 +- 3V" and by TPVAD: "Reference Voltage VAD: 205 +-5V.

I do not think these test points are the reference voltages, as they have some transient activity (scope images coming, need to get them off of the scope). The schematics in the service manual have fonts so small they are nearly unreadable! Is there a readable version available somewhere?

I'm going to try:
1) Find the DC reference voltages Vscn and VAD and probe them.
2) Find out what these transient signals should look like. What should I see at TPSN1 and TPVAD?

[raftman]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

On TPSN1 there are series of pulses that repeat at 60Hz. I'm measuring TPSN1 with respect to ground (using the P2 connector). The pulses change between about 3 levels (-50V, 200V, 300V, approximately). The series of pulses lasts about 8ms, then the -50V remains until the next period begins.

Could anyone tell me what I should be seeing here? I've read a little bit about how the pixels are reset and cleared, but I have no idea if this waveform is bad or not.

Or maybe that IS the problem - TPSN1 should be a DC voltage Vscn, and obviously it is not on my tv.

I'll post my plot from TPVAD shortly.

[raftman]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

TPVAD has similar looking pulses. I'm attaching a zoomed in image. Does someone have reference waveforms or could someone describe what they should look like?

BTW - Vsus is clean at ~215V.

[tw2005]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

I can't help with the waveforms. But I believe from my experience those reference voltages should be within spec as shown and I have found them to be when using a multimeter.

I am wondering since both those pairs of IGBTs you replaced are part of the VAD cct and that is low if that's the area causing this issue.

You said you're 100% sure these are soldered in ok, we have had the odd failed repair reported where people have not soldered these in well enough(the tab) but you do sound like you've got a good idea of what's right.

Not sure, apart from rechecking those and the gate resistors, maybe one of the driver ICs or the small 5 pin npn pnp transistors is bad.

I'm guessing though

[tom66]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

TPVAD has similar looking pulses. I'm attaching a zoomed in image. Does someone have reference waveforms or could someone describe what they should look like?

BTW - Vsus is clean at ~215V.

Looks like your set-up ramp is truncated. The flat portion with the end spike should be a slow ramp up to Vsus. Same for follow flat portion. Low Set-Up will cause a distorted, underdischarged image.

[raftman]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

You said you're 100% sure these are soldered in ok, we have had the odd failed repair reported where people have not soldered these in well enough(the tab) but you do sound like you've got a good idea of what's right.

Not sure, apart from rechecking those and the gate resistors, maybe one of the driver ICs or the small 5 pin npn pnp transistors is bad.

I'm guessing though

I used a heating gun and added flux to the pad before reheating. When they were hot I brought in some solder to the tab (the bottom pad) and watched some solder get sucked underneath the part. I think the soldering connections are good. Soldering problem was my first thought too. I'll try next to check the driver IC after reviewing some other threads that might be helpful.

Looks like your set-up ramp is truncated. The flat portion with the end spike should be a slow ramp up to Vsus. Same for follow flat portion. Low Set-Up will cause a distorted, underdischarged image.

I annotated my original plot since the voltage scales weren't well labeled. Could you point out the ramp you are referring to? The waveform begins at a negative voltage (maybe -50V, I don't remember exactly) and then pops up to ~210V (Vsus I assume). Then there's a steep ramp up to over 300V, followed by a shallower ramp before a jump up to ~430V. Then it drops to Vsus before starting a negative ramp down to -50V again. If you can draw on the picture that would be very helpful.

If it's a timing issue maybe a bad cap is shortening the ramp. I'll have closer looks at the schematics.

BTW, this will be a background project for me this week so it might take a couple of days to get an update - but I am actively working on it and appreciate your time and helpful responses.

[tom66]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

You're probing the Vscan output which is about 150V above the Vfg output (it's exactly Vscn above it.) So, subtract 150V from that. Your wave will start at -200V, and should go up to Vsus in a single ramp. These Panasonic sets do not have a Vset ramp that is greater than Vsus, they keep the whole set-up portion below Vsus.

The flat sections are the problem, as you've highlighted. Panasonic appear to use the SUS IGBTs to finish off the waveform - that part is working. But the FET/IGBTs that do the ramp up portion are not working for some reason.

Basically, output can be in three major states: -Vad (-190~-200V), GND, or Vsus (~210V) or it can be ramping between them. Note that it's a coincidence that Vad ~= Vsus on this panel; other panels are different.

Some images from a 2008 plasma panel. Similar, but yours will have less reset portions to get lower black level (MLL):
https://www.badcaps.net/forum/attach...6&d=1413756676

[raftman]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

You're probing the Vscan output which is about 150V above the Vfg output (it's exactly Vscn above it.) So, subtract 150V from that. Your wave will start at -200V, and should go up to Vsus in a single ramp. These Panasonic sets do not have a Vset ramp that is greater than Vsus, they keep the whole set-up portion below Vsus.

The flat sections are the problem, as you've highlighted. Panasonic appear to use the SUS IGBTs to finish off the waveform - that part is working. But the FET/IGBTs that do the ramp up portion are not working for some reason.

Basically, output can be in three major states: -Vad (-190~-200V), GND, or Vsus (~210V) or it can be ramping between them. Note that it's a coincidence that Vad ~= Vsus on this panel; other panels are different.

Some images from a 2008 plasma panel. Similar, but yours will have less reset portions to get lower black level (MLL):
https://www.badcaps.net/forum/attach...6&d=1413756676

thank you - I will study the schematic a bit and test a few relevant components. My original compliant still stands - the schematics in the service manual have unreadable REFDES and net names! Are better, readable versions available?

[tw2005]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

thank you - I will study the schematic a bit and test a few relevant components. My original compliant still stands - the schematics in the service manual have unreadable REFDES and net names! Are better, readable versions available?

no, not for free anyway. not sure if this is some form of locking the doc or not.
2011 docs on are like this and it gets worse, P boards start dissapearing too.

I do have a 50GT30A Brazil manual which will be similar design and components just thatthe 42 has the buffers included

[raftman]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

no, not for free anyway. not sure if this is some form of locking the doc or not.
2011 docs on are like this and it gets worse, P boards start dissapearing too.

I do have a 50GT30A Brazil manual which will be similar design and components just thatthe 42 has the buffers included

I suppose that's fair for them to protect their schematics. That is really detailed IP. Are you offering the 50GT30A manual or do those schematics have the same issue? If it has the same structure and I can read the net names it might help me. Basically I just want to find the connections from my probing point to VAD, GND, and VSUS and see which devices to check. I could do it with what I have now but it will take some time. I should be able to spend some time on this tonight. I might not update for a few days - but will come back either way with a result eventually. Thanks!

[tw2005]

Re: Panasonic 42" TC-P42S30 *almost* fixed. 14 blinks -> snowy image bad color

I suppose that's fair for them to protect their schematics. That is really detailed IP. Are you offering the 50GT30A manual or do those schematics have the same issue? If it has the same structure and I can read the net names it might help me. Basically I just want to find the connections from my probing point to VAD, GND, and VSUS and see which devices to check. I could do it with what I have now but it will take some time. I should be able to spend some time on this tonight. I might not update for a few days - but will come back either way with a result eventually. Thanks!

.