Samsung Power Supply Board BN44-00874F

[Nicktronic]

Hi, I will get to this, just been really busy!

[Davi.p]

Search in secondary side for a TL431 or equivalent in sot23 and replace it, 5,5v is too low, before it check the main stage ic primary side with its datasheet, if vcc is as usual around 16v then is so..

[Nicktronic]

what you use to remove the insulating glue? primary side of the two transformers tested? CM801s , CM802s, DM807 Tested? what voltage on cathode of DM807?

I used isopropyl, a brush and a plastic spudger. All components tested good. Cathode of DM807 on power up was 5.45VDC slowly discharging at a rate of 0.01vdc/second

[Davi.p]

what you use to remove the insulating glue? primary side of the two transformers tested? CM801s , CM802s, DM807 Tested? what voltage on cathode of DM807?

[Nicktronic]

All the SMD resistors test fine as far as I can tell.

[nomoresonys]

You don't see a resistor there because there isn't one.

[Davi.p]

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

[Nicktronic]

it is under the legs of the mosfet

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

[Davi.p]

it is under the legs of the mosfet

[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]

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]

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.

[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 ??

[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!)

[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]

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.,..

[nomoresonys]

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

[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..

[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

[Nicktronic]

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

4.2kohms in both