Samsung TV UN75NU7100/Power Board BN44-00874C

[EazyBone]

I can't get the old spare board to stop popping. Not sure what's wrong. But I have compared the cold side leds parts, and something is off on the board that's flashing. No idea what. The mosfets on the flashing one read 3megaohms and climbs to 50m ohms

The mosfets on the, probably good but popping board reads 4.6mohms steady (led cold side)

[valvashon]

On my Samsung board I had a bad dual diode unit that was between the similarly numbered MOSFET's- you might check that if it exists on your board. The first couple of numbers of our PS boards are the same but they are quite different boards.

https://www.badcaps.net/forum/troubl...rd-blows-fuses

[Larrob19]

Well that sounds like some good news. Good luck in your search. I'll be watching closely .

[EazyBone]

So I figured out the old bad board. Original what blew was the other mosfets up top in the picture. The main caps were shorted because those mosfets were shorted. Replaced and tv fires right up. Now that I have a working good board, maybe we can help the OP and me figure out the old board with the blinking leds. I'd assume it's probably a similar issue?

What can I do with good board to help test the led areas for us both?

Edit. I call everything that looks like that a mosfet lol don't know if that's true.

[EazyBone]

So the only discrepancy I have found so far is.

When I check the voltage on pins 10 and 11 on the bad board I get 1.8 volts. When I check it on the good board against 0.005 volts or nothing.

So far the other voltages to the LEDs seem correct except for these two pins. I'm kind of just probing around maybe you can check what you get on 10 and 11 using the chassis ground and check the voltage on that jp949 hole the probe is in in the picture. Seems these are connected

I'm doing the tests with the PSU out of the TV as a standalone.

Also I am tracing the line, can't figure out where it goes. Any help?

[EazyBone]

So when plugged into the tv, those same spots read 190v ground chassis on good board. And fluctuates voltages when plugged in on bad board. No idea what that means. I'm not able to help ya any further if no one else can point me in a direction. I can't learn if I don't know what to look up or how to find it and I've searched pretty through for a solution. Sorry

But at least we have same problem and it seems like it's the power board for you.

When I keep all ribbons connected to the Tv and only disconnect the PSU from the LEDs (with the bad board) I still was able to get a startup sound, which sounds like you are not getting. So who really knows.

Tried to help.

[nomoresonys]

With fluctuating voltages you might want to check over capacitors and voltage regulating diodes.

[Larrob19]

I checked my board and I get 281v at pin 5 and 10 and nothing at the other pins and nothing at jp949. The other pins are millivolts.

[Diah]

rework yours MOSFET , not any part new are new..

[EazyBone]

I checked my board and I get 281v at pin 5 and 10 and nothing at the other pins and nothing at jp949. The other pins are millivolts.

Is that connected to lights or on bench

[Larrob19]

Bench

[Larrob19]

Is this of any help.

[nomoresonys]

Wonder if it might be a bad led driver IC on the powerboard. Suppose if one of you has a working model on the bench you can test the pins of the working tv led driver IC against the non-working tv. May need the datasheet.

[EazyBone]

Yea, I do have working one. I don't know where the IC is, definitely something I can test if pointed in the direction

[nomoresonys]

I can't see a clear sharp image of none of these boards, maybe check out Bobby here he knows what hes doing: https://www.youtube.com/watch?v=xjVt14h_af4

[Larrob19]

I viewed the video but nothing seems to help in my situation.

[nomoresonys]

As per the video, IF you plug in the powerboard by itself, NOTHING else hooked up and you don't have around 400 volts on the big filter caps, you have a pfc/power factor correction issue. You need to at least fix that issue. Honestly in your situation, I think a replacement board is your best bet.

[nomoresonys]

It's a good sized tv, if you are happy with the picture and everything it could be worth a replacement board. It is a samsung and they have fallen off in reliability but who knows, if you don't push the backlights too hard you may get some more use from it. Myself I wouldn't buy a new samsung or invest much in repairing one, just WAY too many panel faults in last decade or so.

[Larrob19]

Yes I think your right about the PFC. I plugged it in to check the voltage on the 3 big caps and it's showing about 60v. Also after checking the two Mosfets that I changed originally 1 was burnt again. I think it's time to dig a hole and bury it in the back yard.