Samsung Power Supply Board BN44-00874F

[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]

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.

[nomoresonys]

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

[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 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]

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.

[Nicktronic]

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

4.2kohms in both

[Nicktronic]

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?

QP801CS (new) - 167vdc
QP802CS (new) - 167vdc

QM801CS - 125vdc
QM802CS - 8vdc

[Davi.p]

What a disaster of discussion, plenty errors, you did not noticed the low value shunt resistor hidden under QP802, that is ALWAYS present in such circuits, it have to be open , check from source legs to Negative and you find it open...cmon..

[nomoresonys]

Reported that verbal abuse. Wonder if this site will ever do anything more than just delete the remarks??

[Davi.p]

Is it important to help someone and remark the errors or mime to be an expert and set the user always or often in the wrong way? Bah.,..

[Nicktronic]

What a disaster of discussion, plenty errors, you did not noticed the low value shunt resistor hidden under QP802, that is ALWAYS present in such circuits, it have to be open , check from source legs to Negative and you find it open...cmon..

QP801CS - source to neg - 0.24 ohms
QP802CS - source to neg - 0.24 ohms

QM802CS - source to neg - 0.22 ohms

[Davi.p]

when you shot the picture of board? Under i see glue still all around QP802, but i see scratched glue around QP801, furthermore 801 & 802 are in a separate circuit not as usual, so i expect another low value resistor on the source of QP801, i don't see well with the glue.. another thing is that you have no stby voltage, but i see not where you say you've tested all big diodes on heatsink (DM85x..)... to be clear, the standby voltage is 7,5v and rises to 12.5 when activated.. where do you measure the output? under, with maybe a little film of glue ? or on the pins? you can measure on the center pin of the 4 TO220 diodes, components side (eye to slipping probe!)

[nomoresonys]

when you shot the picture of board? Under i see glue still all around QP802, but i see scratched glue around QP801, furthermore 801 & 802 are in a separate circuit not as usual, so i expect another low value resistor on the source of QP801, i don't see well with the glue.. another thing is that you have no stby voltage, but i see not where you say you've tested all big diodes on heatsink (DM85x..)... to be clear, the standby voltage is 7,5v and rises to 12.5 when activated.. where do you measure the output? under, with maybe a little film of glue ? or on the pins? you can measure on the center pin of the 4 TO220 diodes, components side (eye to slipping probe!)

So where is this imaginary resistor ??

[Nicktronic]

when you shot the picture of board? Under i see glue still all around QP802, but i see scratched glue around QP801, furthermore 801 & 802 are in a separate circuit not as usual, so i expect another low value resistor on the source of QP801, i don't see well with the glue.. another thing is that you have no stby voltage, but i see not where you say you've tested all big diodes on heatsink (DM85x..)... to be clear, the standby voltage is 7,5v and rises to 12.5 when activated.. where do you measure the output? under, with maybe a little film of glue ? or on the pins? you can measure on the center pin of the 4 TO220 diodes, components side (eye to slipping probe!)

Just to be clear you are talking about QP801/802 and not QM801/802?
I've attached cleaned up pictures.

I tested all diodes and MOSFETs on the board and all are good, still no standby voltage.

[Davi.p]

Nicktronic you first said you tested QP802.. how did you tested? if it were shorted as usual D to S it couldn't not having broke also that shunt resistor under it..

[Nicktronic]

Nicktronic you first said you tested QP802.. how did you tested? if it were shorted as usual D to S it couldn't not having broke also that shunt resistor under it..

Yes, it was shorted D to S. Where is the shunt resistor? Is it on the underside of the board, or under the heatsink?

[Davi.p]

it is under the legs of the mosfet

[Nicktronic]

it is under the legs of the mosfet

I can't see a resistor under the legs, only jumpers.

[Davi.p]

very difficult to see through the glue, for me you have to check all these components under here: