Samsung Power Supply Board BN44-00874F

[nomoresonys]

Maybe check youtube, if you look hard enough, you can find some good videos that tell you what to check and what drives what etc. A picture is worth a thousand words and a video is worth a million words imo.

[nomoresonys]

So if everything else checks out then the pfc IC must have been damaged, which is likely to to happen in a case like this where that particular shit that blew up on your board and pretty much everything else has been tested. Guess you should look hard at that, thoroughly test it if you can.

[nomoresonys]

I noticed you were doing some testing with the board live, can you test the voltage of the collector/source pin of that pfc transistor?

[nomoresonys]

So if it's back in check the resistance and compare it to CM814.

[nomoresonys]

If you still had it out you could have tested the resistance of the holes it goes in. Guess you can test that with it in there.

[Nicktronic]

Did you replace CM810?

No, I pulled it and tested it. Was like 93uF (it's 100uf rated). I suppose I could test it with DC supply and put 50VDC on it (it's a 63vdc cap)

[nomoresonys]

Did you replace CM810?

[Nicktronic]

I'm at a loss....everything I've checked seems ok, but I'm having trouble following the circuit to understand exactly where the 10VDC (that should be 14-29) is sourced from. It appears to start tapped off that big transformer and through a diode, but how is the TXFMR producing V without any switching happening. Does anybody have a schematic close to BN44-00874F?? Can anybody confirm that this board should be fully on when on the bench (like other samsung power supply boards), or do I need to install it?

[Nicktronic]

Well test QP802CS, should prolly test the same as QP801CS, the numbers on them are the same, yes?

Rechecked, they are good and the same.

[Nicktronic]

Seems like we covered most of the potential faults, if it's not a bad solder, resistor, cap, guess that leaves the pfc IC. Guess you can check it for a short. I believe there's only one ground, maybe check, with tv unplugged, neg probe on neg leg of filter cap/hot ground, positive probe on each pin of IC, make sure only one pin has continuity as in only one will show 0 ohms or beep in continuity/diode mode if meter has that feature, same as testing a fuse.

Checks out ok, no shorts

[Nicktronic]

Well, if this is a frequent malfunction, check the other components that are in the Repair list...

Yes lotas, this is exactly what I did to start the repair. But I'm still having this issue. I will check again though...

[nomoresonys]

It would be easy enough to change out all the parts listed at the bottom of that parts kit. Those 4 blue caps and the 2 transistors, one of which you already changed out.

[nomoresonys]

Well test QP802CS, should prolly test the same as QP801CS, the numbers on them are the same, yes?

[nomoresonys]

With power applied on the bench, CM814 and CM815 have 10VDC, equal to the VCC of ICM801S, but CM810 reads 0VDC. Not sure what role it exactly plays, but there should be something right? Sure would love a schematic! 😬

What ohm reading are you getting on that cap?

[lotas]

Well, if this is a frequent malfunction, check the other components that are in the Repair list...

[nomoresonys]

Seems like we covered most of the potential faults, if it's not a bad solder, resistor, cap, guess that leaves the pfc IC. Guess you can check it for a short. I believe there's only one ground, maybe check, with tv unplugged, neg probe on neg leg of filter cap/hot ground, positive probe on each pin of IC, make sure only one pin has continuity as in only one will show 0 ohms or beep in continuity/diode mode if meter has that feature, same as testing a fuse.

[nomoresonys]

I would switch it out. Sometimes it's just easier, specially if you don't have an accurate cap tester.

[Nicktronic]

With power applied on the bench, CM814 and CM815 have 10VDC, equal to the VCC of ICM801S, but CM810 reads 0VDC. Not sure what role it exactly plays, but there should be something right? Sure would love a schematic! 😬

[Nicktronic]

If you have not, check DP802 and 803 Diodes on underside of board by the big caps. Also double check all those resistors, make sure none are open or drifted.

They test good.

Which resistors? I've checked all the through ones and think they're ok.

[Nicktronic]

I wonder if CP810 is ok.

Good