Samsung UN55EH6050F power supply short

[ggil44]

Hello, I have a Samsung UN55EH6050F TV that suddenly quit and upon inspection, I found the fuse in the power supply was blown. I removed the board and I replace the fuse and plugged in the power supply board by itself and immediately, the fuse blew again. The power supply board is BN44-00499A / PD55AVI_CHS. I used a capacitor checker and found all but the 450v 100uf capacitor to check out good. I removed the 450v cap and rechecked it, and it checked good out of the board, so I re-soldered it back into the board. I then checked the diodes, which seemed to check good. I carefully inspected the board, but I can't isolate the problem and there are no burn't components or bulging caps or any visual indication to guide me to the faulty component. Any help you can offer would be greatly appreciated. I would include a picture, but it looks no different from the stock BN-00499A / PD55AVI_CHS power supply board.
Thank you in advance for your help,

[lotas]

Re: Samsung UN55EH6050F power supply short

It looks like your fault.
https://www.badcaps.net/forum/showthread.php?t=82862

[ggil44]

Re: Samsung UN55EH6050F power supply short

Your right, it IS my fault. I bought the TV.

Thanks for the reference link.

[R_J]

Re: Samsung UN55EH6050F power supply short

Check if VX801S is shorted.

[ggil44]

Re: Samsung UN55EH6050F power supply short

Hello R J, I checked VX801S both in and out of circuit and got a 900 meg ohm reading so I don't think that is the culprit or as "lotas" would say, fault.
Thanks for the suggestion though.
Regards,

[ggil44]

Re: Samsung UN55EH6050F power supply short

From the link I got from Lotas, I checked QL801 and QL802, after uncovering them from the white silicone covering their identifiers and found them to be shorted just like in the link he gave me. Now I am waiting for the replacement mosfets to replace the bad ones.
Thanks again Lotas!

[Davi.p]

Re: Samsung UN55EH6050F power supply short

You bought the tv?? It is different model! VX is a varistor i think, it must sign OL..
QL801/2 what signs?

[ggil44]

Re: Samsung UN55EH6050F power supply short

Hello Davi P. I'm not sure that I follow your post. The TV is a Different model, but the power supplies appear to be the same and have the same board numbers as the UN50EH5300F, which is BN44-00499A.

Regards,

[Davi.p]

Re: Samsung UN55EH6050F power supply short

"Your right, it IS my fault. I bought the TV. " ... what do you mean?

[ggil44]

Re: Samsung UN55EH6050F power supply short

Hello Davi.P, OK, I was just bantering with lotas because in my original post I had said "...guide me to the faulty component. Lotas picked up on that and said "It looks like your fault." He is right since it is my TV and there are "faulty" components, it is my (problem), "fault" that I need to fix. I was just joking around with lotas. Hope that clears it up.
Regards,

[ggil44]

Re: Samsung UN55EH6050F power supply short

OK, I finally got the 2 mosfets (QL801 and QL802) and checked them a soldered them into the board, held my breath and plugged in the board. It immediately blew the fuse again so evidently the mosfets were the casualty not the cause. I ended up taking the same route as neilc6 and getting another power board and the TV works fine but I would still like to know what is causing the short in the old power board. Any other suggestions?
Thanks,

[Davi.p]

Re: Samsung UN55EH6050F power supply short

VX801 is the varistor, it must mark open, not 900Mohm, remove it and test the board again

[ggil44]

Re: Samsung UN55EH6050F power supply short

Hello Davi.p, I did remove the varistor and tested it out of circuit. I found it to test open as you suggested.
Regards,

[R_J]

Re: Samsung UN55EH6050F power supply short

OK, I finally got the 2 mosfets (QL801 and QL802) and checked them a soldered them into the board, held my breath and plugged in the board. It immediately blew the fuse again so evidently the mosfets were the casualty not the cause. I ended up taking the same route as neilc6 and getting another power board and the TV works fine but I would still like to know what is causing the short in the old power board. Any other suggestions?
Thanks,

If the mosfets were shorted, it is very likely the gate drive diodes or resistors are defective or maybe even the gate drive transformer may be open.
When the mosfet shorts drain to gate, it will supply the full 165v to the gate and destroying the gate drive circuit

[ggil44]

Re: Samsung UN55EH6050F power supply short

Thanks R_J. The mosfets were indeed shorted so I will check the "gate drive diodes & resistors" and also the transformer. I appreciate the help.

Regards,

[ggil44]

Re: Samsung UN55EH6050F power supply short

With all the festivities surrounding Christmas, I have decided not to search for the failed components on the power board. I did get a working board and the TV is working fine.
Thank you all for your good suggestions and help. Wishing you all a happy Christmas season.