BN44-00338A Samsung PSU

[johnboy1313]

I found an LN26C450E1D in the trash. It has the BN44-00338A PSU in it. It was completely dead when I got it. No standby light, no standby voltage. The main fuse was blown, CP814 was completely burnt, and QP8015 was shorted. I replaced all three and now I get the solid red standby light, 5V at A5V, and 167V at the main cap. Ive found threads with the same PSU with very similar symptoms, but they all have 390V when powered up suggesting that their PFC block was working. I don't think mine is. When I hit the power button, PS_ON tries to go high for a split second but then drops back to 0V. I tried forcing the PSU on with a resistor with no success.

RP802 reads .1 ohms. I believe it's supposed to be a .12 ohm resistor, but my meter will only read to one decimal point in the ohms setting.

DP802 checks good.

I checked the pins at ICP801 and got the following...

Pin 1 INV - 1.6V
Pin 2 MOT - 0V
Pin 3 COMP - 0V
Pin 4 CS - 0V
Pin 5 ZCD - 0V
Pin 6 GND - 0V
Pin 7 OUT - 0V
Pin 8 VCC - 11.5V

I'm not sure if the IC is bad, or just not getting the signal from something else to turn on. Like I said, aside from 5V at pin A5V, there is no sign of life.

I've attached the schematic for the PSU. Thanks!

[johnboy1313]

Re: BN44-00338A Samsung PSU

Pictures

[CapLeaker]

Re: BN44-00338A Samsung PSU

Look hard at the gate drive circuit of the 10n60 and probably the PFC IC is toasted too.

[johnboy1313]

Re: BN44-00338A Samsung PSU

I already changed the 10n60. I misidentified it in my original post as QP8015, it is actually QP801S. I just found a FAN7530 PFC IC on another Samsung PSU that had a bad inverter transformer. I swapped it onto this board and that seems to have been the problem. I'm not sure what caused it, but in the end, I've got a ceramic cap, a 10n60 mosfet, a fuse, and that IC into it. Thanks for the tip CapLeaker.

[budm]

Re: BN44-00338A Samsung PSU

It is always best to replace the IC that drives the MOSFET at the same time, you are lucky that the IC Gate drive output pin was not stuck on HIGH which will damage the new MOSFET.

[CapLeaker]

Re: BN44-00338A Samsung PSU

Glad you got her going!

[tom66]

Re: BN44-00338A Samsung PSU

When the FET fails often the drain-gate junction will short too. This will lead to a large current being shoved into the gate driver of the PFC IC. I've had ICs fail by shorting to supply - this would obviously be bad as the FET would be stuck on (leading to a loud bang when powering it up!)