Samsung 50" plasma PS50Q97 with a dead main board

[dokma]

Hello forum!

This is my fourth post so I will try to start on the right foot by doing it properly right off the bat. I bought this plasma faulty to play around with. The main board is completely burnt. When I unplug everything but the power supply and the main board and I plug in the power chord I get plenty of smoke from the main board.

Now, the model of the TV is a bit of a detective work. I couldn't find the model of the TV anywhere on the back cover or inside so I deduced it from the main board codes. SO I THINK this is PS50Q97.

Now, since the board is toasted, I decided to buy a new main board. The reason I am posting this is because I would like NOT to toast the new board when I plug it in. So, the bottom line is, how do I make sure I do not toast the board I plan on getting from EBay? The reason I ask this is because I presume it is not impossible that something else is faulty on the TV and that, once I plug everything up again, that other thing might kill the new board.

TV MODEL DEDUCED: PS50Q97
Main board codes: BN40-00112A BN94-01177D

Replacement board: https://www.ebay.co.uk/itm/164241011...m=164241011686

[tvtimmy]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Run the test patterns on the set. If they show up, the rest of the tv is good. Post a picture of your control board and I will show you how to test it.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

So to clarify, once I receive the new main board I need to plug everything up, plug the mains and run the test patterns? There is no danger of the main board getting fried again just from the act of plugging everything up and connecting to the mains?

I will post the pictures tomorrow.

p.s. The main board is on the way.

[tvtimmy]

Re: Samsung 50" plasma PS50Q97 with a dead main board

You can run the test patterns now. I don't know how to do it on these old Samsungs though.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

You can run the test patterns now. I don't know how to do it on these old Samsungs though.

Without the main board? I've never ran test patterns or read anything about it. I'll go search the forum on how that is done. So running test patterns without the main board is perfectly possible?

[tvtimmy]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Yes. It uses the logic control board to generate the patterns.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Ok, so I've got the main board. I've plugged everything up, connected the mains and poof. I get visible flames on the main board under the elevated metal shield. I hope my broken TV didn't burn out a working main board. This is exactly what I was worried about...

Is there any way I can be certain the main board itself was faulty instead of me owning a mainboard frying TV?

Due to lack of consideration I forgot to plug the cables goin to the main board one by one so now I do not know what would happen if I connected only the power supply with the main board.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Finally back from vacation!

I have found the test patterns instructions for this set and as I was about to implement them my PSU started clicking off! So now I have a new fault on my hands. I jumped PS_ON to ground while having all the cables disconnected to see if the relay will stay on but nope. Still clicking off. So now I have to fix the PSU before I can get to the test patterns. Today I'll check the common stuff with cold solder joints, transistors and diodes.

I couldn't produce any images of this set that were worth of uploading so I found a good one by another poster and I am attaching it here.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

So, some new measurements here. I checked the 3 leg rectifier diodes in diode mode and I get a beep and a 0 reading when I check between the outer pins as marked on the image. From what I understand about SMPS designs those two pins should come from different rails on the transformer output and should not be shorted. Otherwise it could've been just a normal, fast diode. Can you tell me if I'm correct in concluding that those rectifier diodes are shorted?

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

No, they are two anodes in parallel, in every TV circuit I've seen them being used those pins are always shorted by the trails on the PCB.
The correct way to determine if there's a short is to measure between the middle and leftmost or rightmost pin.

Do you have VS and VA when the clicking occours?

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Ok, I will measure the VA and VS if possible. The click off comes very shortly after the click on. Note that this PSU was functional just recently but I somehow managed to get it broken in the process of trying to run the test patterns.

Is it of any use to try and force the relay on to see where the short (if it is a short) is or is it too dangerous?

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Oh, by the way, is this set perhaps one of those where the PSU goes off by design if not all of the boards are plugged in? I tested the PSU by only having the mains connected to it and jumping PS_ON to ground but it clicks off...

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Are there are other _ON pins? Like VS_ON but at 0V, maybe that can trigger this relay clicking.

Even if the PSU is bad, what exactly failed at the main board?

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Are there are other _ON pins? Like VS_ON but at 0V, maybe that can trigger this relay clicking.

Even if the PSU is bad, what exactly failed at the main board?

I think there is VS_ON. I will check it today after work. Main board got shorted. Then I bought a replacement one and that one burnt out before my eyes with visible flames. So the PSU was working at that point. Then I went to try the test patterns but now the PSU is clicking off.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

How does my 5.3V rail jump to 19V on power on???

So finally I got about to measuring things properly. These are the voltages I took from CN807 when the PSU is plugged into the mains and nothing else:

STBY : 5.11
VS-ON : 0
NC : 0
PS-ON : 4.19
RTN : 0
5.3V : 1.74
RTN : 0
RTN : 0
5.3V : 1.74
5.3V : 1.74

The 5.3V test point also gives 1.74V

Now the interesting part is the measurement I got when jumping PS-ON to RTN and taking the measurement at the moment I plug into the mains.

My 5.3V test point jumps to 19V and then slowly drops off after the relay clicks off. How does my 5.3V rail get 19V on it? No wonder the mainboard I plugged into this TV burned out. I hope nothing else got fried from this.

New pictures attached.

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

The mainboard doesn't receive the 5.3V signal, that's for the logic board, only 5V/18V/12V.

Trace that 5.3V on the power supply to see what's wrong with it.

I'll be uploading a service manual which is useful in this case, pages 71 and 72 show all the connectors and their pinouts.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

The mainboard doesn't receive the 5.3V signal, that's for the logic board, only 5V/18V/12V.

Trace that 5.3V on the power supply to see what's wrong with it.

I'll be uploading a service manual which is useful in this case, pages 71 and 72 show all the connectors and their pinouts.

By tracing you mean going down the rail and checking all the components or is there more to it?

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

https://www.amazon.co.uk/CLICKING-Sa.../dp/B00H97REEM

Found a repair kit that also list the defective parts for "psu clicking", that may be your fault. And I have a schematic for this PSU too, page 4, good for troubleshooting this 19V in the 5.3V rail problem.

You logic board is probably the one who lit on fire if this 19V spike was happening at power up.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

https://www.amazon.co.uk/CLICKING-Sa.../dp/B00H97REEM

Found a repair kit that also list the defective parts for "psu clicking", that may be your fault. And I have a schematic for this PSU too, page 4, good for troubleshooting this 19V in the 5.3V rail problem.

You logic board is probably the one who lit on fire if this 19V spike was happening at power up.

I think I'm using the terminology incorrectly. How do you call the board that is connected to the PSU via CN807? I referred to that board as main board.

The schematic you provided is really helpful. I'm betting on ICX802 going short and passing the transformer output current directly into the 5.3V rail. That probably also means that all the caps after ICX802 that are rated at 10V got fried. Will check if ICX802 gives same input and output voltages.

ICX802 is a 5 legged step down, switching regulator that was supposed to provide the 5.3V rail.

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Logic board is the one connected to CN807, it connects to Y and X-Main boards, main board is the one with the audio/video inputs.

DX808 is a zenner diode that may have been damaged.