Samsung Power Supply Board BN44-00874F

[Nicktronic]

Hey everyone,

This power supply board is hard to find but there are repair kits available. This board had a blown fuse, FP801S, blown PFC MOSFET, QP802CS and ceramic cap, CP809. I replaced them with parts I already had and tested the rest of the parts that would've come in the repair kit and they were fine. I powered the board up on the bench expecting, in typical Samsung power supply board fashion, to see all my output voltages but, nothing. 0 volts on CNL801, CNM801 and CNT801. The only thing I have is 170vdc on the filter caps. No standby voltage either.

Anybody have a schematic for this board? I'm struggling to troubleshoot without it. Also I'm open to advice on where to focus.

Thanks!

[nomoresonys]

Whoa, the soldering of those replaced parts is a mess, that could be the problem.

[Nicktronic]

Yeah, I didn't clean the board up for her photoshoot, but I assure you the solder joints are solid.

[nomoresonys]

I see, I would probably suspect the IC nearby QP802CS, the one with 14 legs there and maybe check the resistors by your mosfet, and maybe QP804 and the ones near it. See if you can grab a datasheet for that IC.

[nomoresonys]

I guess first order is getting the standby working.

[nomoresonys]

Go ahead and check all the transistors, thats all that start with Q for a short if you haven't already. For those that may be looking on and need to know. Put meter in beep mode, thats the one with the diode on some meters and check each of the three legs for a short, so one probe on leg 1 the other on leg 2 then 3, then go from 2 to 3, if you get a constant beep its shorted. If meter has no beep mode, you can test in ohm mode, if you get close to 0 ohms while doing the same test its shorted.

[nomoresonys]

To be clear, you replaced the parts with the correct part and after trying tv again, none of the parts are reading bad again, fuse didn't blow etc?

[nomoresonys]

Not exactly sure, but CP801S and CP802S may need to be checked.

[nomoresonys]

Maybe do a quick ohm check of CM185, CM810 and CM814.

[Nicktronic]

I see, I would probably suspect the IC nearby QP802CS, the one with 14 legs there and maybe check the resistors by your mosfet, and maybe QP804 and the ones near it. See if you can grab a datasheet for that IC.

The IC is ICP801S, UCC28064A G4, datasheet attached.

The resistors beside QP801CS appear to be 0.25ohm each, but when measured out of circuit, both are dead short(0.01ohms each)

QP804 seems ok and the resistors around it are good.

[Nicktronic]

Go ahead and check all the transistors, thats all that start with Q for a short if you haven't already. For those that may be looking on and need to know. Put meter in beep mode, thats the one with the diode on some meters and check each of the three legs for a short, so one probe on leg 1 the other on leg 2 then 3, then go from 2 to 3, if you get a constant beep its shorted. If meter has no beep mode, you can test in ohm mode, if you get close to 0 ohms while doing the same test its shorted.

All the FETS are good, no shorts. Should I check all the transistors on the underside of the board too?

[Nicktronic]

To be clear, you replaced the parts with the correct part and after trying tv again, none of the parts are reading bad again, fuse didn't blow etc?

Correct

[Nicktronic]

Not exactly sure, but CP801S and CP802S may need to be checked.

They are 1uF each and measure 2.1uF in parallel. Seems ok.

[Nicktronic]

Maybe do a quick ohm check of CM185, CM810 and CM814.

They all measure good.

[nomoresonys]

The IC is ICP801S, UCC28064A G4, datasheet attached.

The resistors beside QP801CS appear to be 0.25ohm each, but when measured out of circuit, both are dead short(0.01ohms each)

QP804 seems ok and the resistors around it are good.

Check the markings on those resistors, if it's a 0 ohm resistor then its ok.

[nomoresonys]

All the FETS are good, no shorts. Should I check all the transistors on the underside of the board too?

Sure, couldn't hurt to check them.

[Nicktronic]

Is it fair to say ICM801CS (FA6B22N, cannot find a datasheet) should be driving QM801CS and QM802CS when the board is in standby? It's switching the 170vdc of the filter caps, to ultimately provide an unboosted VDC on the output connector (7ish volts)?

In the current state with the board on the bench and plugged in, on ICM801CS pins:

1 - 68-69VDC
2 - 0vdc
3 - 0vdc
4 - 7.2VDC
5 - 0vdc
6 - 0vdc
7 - 0vdc
8 - 0vdc
9 - 0vdc
10 - 10VDC
11 - 0vdc
12 - GND
13 - 0vdc
14 - 8VDC
15 - 8VDC
16 - 10VDC

https://products.fujielectric.com/en...etail/FA6B22N/

This link is the most info I could find for this IC.

Thoughts?

[Nicktronic]

Check the markings on those resistors, if it's a 0 ohm resistor then its ok.

Markings indicate 0.25 ohms, and two in parallel, so 0.125ohms

[Nicktronic]

Sure, couldn't hurt to check them.

I did, and couldn't find anything...

[lotas]

FA6B22N can be replaced with FA6B20N, not much information...