Samsung UN40F5500 - PSU not working

[anupkg1985]

Re: Samsung UN40F5500 - PSU not working

CS802 is likely ok, CS805 does seem to be a bit low, I would thing it should be above 20v, I would try replacing CS805 47µf/50v
The voltage across CP812 should be around 15v

Its only 9.8v stable voltage on CP812. Also no change after changing CS805. I changed it with 100uf 50v.

[R_J]

Re: Samsung UN40F5500 - PSU not working

I guess 9.8v might be enough vcc for the pfc ic to work, I would also check the voltages on QS801, the collector will be the same as on CS805, the base should be 15.6Vb and the emitter should be about 15v

The power supply does turn on without the main connected, however there is a protection circuit that might be turning the board off, This line is the FAIL_OUT_CT_S line, which could be triggered by the FLAG_CT_S line from the backlight circuit.
You could try turning off the backlights by grounding the BL_ON pin on CNM803, pin6 to see if that stabilizes the voltage

QM852 collector (VCC_IC_P) it needs to be at least 14 volts, so it's emitter needs to be at least 15v as it supplies ICM801's vcc

[anupkg1985]

Re: Samsung UN40F5500 - PSU not working

I'm getting the same voltages as you mentioned 15.3Vb on Base and 15v on Emitter of QS801. I'll check by grounding BL_ON pin to see if there are stable voltages.

[anupkg1985]

Re: Samsung UN40F5500 - PSU not working

I tried grounding the BLU pin however that didn't make any difference. I did observed the voltage on emitter on QS801 is 15v however it drops to 9v on resistor RS802 and it continues as 9v on the line till IC QM852.

[anupkg1985]

Re: Samsung UN40F5500 - PSU not working

I removed ICP801 SEM3050 from the board and now don't see any voltage fluctuation on the main caps. However it's only 172v due to absence of pfc IC also the VCC pin voltage for this IC measure 9.2V when it's on board and now it's 15V on the same pin without IC. Could this IC be at fault? Is there any way to test it?

[dskall]

Re: Samsung UN40F5500 - PSU not working

Did you replace the cap. for the VCC startup circuit? And RS802 has correct resistance?
A supposed replacement for sem3050 gives 10.5v as minimum start up voltage.

[anupkg1985]

Re: Samsung UN40F5500 - PSU not working

Did you replace the cap. for the VCC startup circuit?

Yes I replaced it however no change, voltage was still 9V.

[Diah]

Re: Samsung UN40F5500 - PSU not working

Yes I replaced it however no change, voltage was still 9V.

if you put the power boards in the tv back .. mainboards disconnected from it , just leave the BL socket connected... just tell which voltage you have on the PCB socket which it goes to MB.. and did the BL come on and remain on?

[anupkg1985]

Re: Samsung UN40F5500 - PSU not working

if you put the power boards in the tv back .. mainboards disconnected from it , just leave the BL socket connected... just tell which voltage you have on the PCB socket which it goes to MB.. and did the BL come on and remain on?

Voltages are pretty much same as I mentioned in post#1, irrespective of mainboard connected or not. One of the led strip is not working when tested with LED tester so there is not difference if backlight connected or not. The voltage on main cap is not stable and jumps from 220v to 300v.

[Diah]

Re: Samsung UN40F5500 - PSU not working

Voltages are pretty much same as I mentioned in post#1, irrespective of mainboard connected or not. One of the led strip is not working when tested with LED tester so there is not difference if backlight connected or not. The voltage on main cap is not stable and jumps from 220v to 300v.

i read the first post... but you do know the smasung PCB had pull R which turn on the PFC high to turn on BL if MB not connected.. if BL socket wasnt connected the circuit will be open. PFC not stable.. so you need in case you dont want to repair yours BL LED right now... your work on the PCB will be correct only if you turn it on as stand alone. and see if the issue remain.

[anupkg1985]

Re: Samsung UN40F5500 - PSU not working

Good new, PSU is back online and there are all the voltages present as expected. As mentioned in post #24, RS802 was at fault. It is marked as 10R0 which 10 ohm but when measured it was turned out to be 600 ohms. Just replacing this one solved the issue.
Thanks all who replied on the thread!!

[nomoresonys]

Re: Samsung UN40F5500 - PSU not working

Good work, lots of times people don't want to check all resistors and diodes BUT in many cases, as in this one, it pays off, if you found the bad resistor early, bam done, no chasing ic's, caps, Q's and all that.