Samsun LN32B550K1F with BN44-00261A burnt out IC

[lucidbarrier]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

The backlights did not even flash on for second then. If the backlights circuit is OK the good lamps and bad lamp, the backlightys will flash on for seconds then the protection circuit will kick in to give you that 3-second to black symptom.
Next thing we need to find out if you do have PFC Boosted Voltage or not by checking the DC Voltage between the two legs of the mail filter cap cp815, it should show about 380~400VDC right now in this self test mode, the backlights circuit require this boosted Voltage to operate.

Looks like 166v across the 2 leads, main board unplugged and power cord plugged in

[budm]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

OK, we need to check out the PFC circuit next. Need to check the PFC diodes and may be the DCV at the VCC pin of the PFC IC. I am going to bed now, so I will continue tomorrow.

[lucidbarrier]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

OK, we need to check out the PDC circuit next. Need to check the PFC diodes next, then msy be the DCV at the VCC pin of the PFC IC. I am going to bed now, so I will continue tomorrow.

Yes sir, thanks for the help!

[lucidbarrier]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

OK, we need to check out the PFC circuit next. Need to check the PFC diodes and may be the DCV at the VCC pin of the PFC IC. I am going to bed now, so I will continue tomorrow.

I'm not too sure which diodes are the ones I need to check but those big diodes DP804 and DP810 are not shorted, they test 0F in one direction and .488v in the other direction (in circuit).

I was looking at another thread with a similar board and I am assuming the PFC IC is the FAN7530 at UP801S?

Reference:
https://www.badcaps.net/forum/showthread.php?t=55254

So with the black lead hooked up to the neg - lead of the main filtering cap and the postitive probing the little pads of the IC chip I only saw 2 voltages.
I think that Pin 8 is the VCC. The little dot was located right over Pin 1.

Pin 8: 0.228v
Pin 1: 1.09v

[budm]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

Look at the schematic and then check the DCV with ref to primary circuit GND (Neg. leg of the main filter cap) on E, B, and C of Transistor QB801 to see what you get.
It may be in the protection shutdown mode due to bad resistors: Rb 803~808 which are part of the PFC protection circuit.., also may be bad 15V Zener ZB801

[lucidbarrier]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

Look at the schematic and then check the DCV with ref to primary circuit GND (Neg. leg of the main filter cap) on E, B, and C of Transistor QB801 to see what you get.
It may be in the protection shutdown mode due to bad resistors: Rb 803~808 which are part of the PFC protection circuit.., also may be bad 15V Zener ZB801

While I was looking for that QB801, I noticed that there have been a bunch of components replaced on this board. There are diodes and capacitors and little resistors and FETs replaced. Some of the soldering is kind of iffy. The larger things look good but some of the tiny SMD components look a bit crooked. He didn't trim the legs far enough on the STRW6252. I went ahead and sent for a return on this board. It's one thing trying to find a failed component on a virgin board but then it's another trying to fix something he might have caused repairing the board.

So the other day I went ahead and ordered this kit, which the seller blanked out the numbers on the components but it looks like a STRW6252 and a FAN7532 is in the kit, as well as some caps and a replacement fuse. I also ordered a Weller WES51 and a few tips, in case I need to replace that IC. I am going to focus on the failed original board and send the Frankenboard back to the seller.

[lucidbarrier]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

Wow that WES51 temp controlled soldering iron really makes a difference! I wish I had bought this thing years ago.

I noticed that the power IC has heatsink compound on it. What kind of heat sink compound do I need to use? All I have is Artic Silver 5 but that contains silver and this looks like the old school white stuff.

[heavymachines]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

Grease will still work just fine.

[lucidbarrier]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

Grease will still work just fine.

Thanks, I bought some GC heatsink compound today at Altex. It says perfect for power ICs so that's the main reason I got it.

[lucidbarrier]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

So today I put some compound on the power IC, soldered it in and swapped out the fuse that was open. I decided not to replace the little FAN7530 IC and to check the voltage at the main filtering cap to see where we were.

I plugged in the power cord and the backlights immediately came on and I saw about 386v at the filtering cap. So I reattached the T-Conn and main board and threw on the rear cover to test it.

And it came on with a beautiful picture! I knew this TV had a lot of potential because of similar TV's I've repaired. Do I need to worry about that little FAN7530 IC?

I want to thank you gentlemen for your help and suggestions.

[budm]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

PFC Voltage booster is working so the PFC IC is fine, glad to see the TV is working again.

[vinceroger69]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

glad you have managed too get your set working is it possible for future reference too let us know what was included in the kit and the board location numbers as it may help others with fault finding etc.

[lucidbarrier]

Re: Samsun LN32B550K1F with BN44-00261A burnt out IC

glad you have managed too get your set working is it possible for future reference too let us know what was included in the kit and the board location numbers as it may help others with fault finding etc.

The TV would power on and you could hear a chime, and the standby light blinked but there were no backlights, no picture, no image on the screen with a flash light on it.
The obvious parts that were faulty were the little power transister and the blown fuse. The power switch was visibly blown and destroyed and the fuse tested open in circuit.

Location UM801S - Power Switch Part# STRW6252
Location FS801 - Fuse T3.15AH 250V

I bought the kit from here:
https://www.ebay.com/itm/Samsung-BN4...2/142490605351

It's mostly the capacitors to recap the board along with the two parts mentioned and a FAN7530 at location UP801S on the back of the board. It's missing one cap though, I'm not sure which revision they used but there is a cap at CM852 rated at 10v 1200uF 105C and it's not in the kit. The cap they have at CM851 isn't on either board I have, and it's a 25v680uF cap. If you do need to replace the STRW6252 then you would also need to have some heat sink compound handy because its bare. I picked GC Type 44 Heat Sink Compound part# 10-8118

But I would read the other posts in this thread because Budm really broke it down how to test the power supply issue.