Samsun LN32B550K1F with BN44-00261A burnt out IC

[lucidbarrier]

Hi everyone
I just recently acquired a nice little Samsung LN32B550K1F 32" LCD TV that wouldn't power on.

Looking at the power supply/inverter board BN44-00261A , it appears that the component at location UM801S is completely destroyed.

It seems that similar inverter/power boards have that same IC pop on it. Shop Jimmy has a video about installing a kit for a BN44-00264B. I was able to locate a schematic and it appears that component is a STR-W6252 , althought I have no idea what it does. I thought it was a MOSFET but it has too many legs.

The only thing I was able to find about this IC was in another thread:
https://www.badcaps.net/forum/showpo...86&postcount=6

Ah, we had a power board like this on badcaps before, giving similar problems.

Try checking ZD803 and ZD804 for shorts.

If they are OK, replace UM801S (STR-W6252) and CM808.

I cannot seem to find a CM808. There is a component right next to UM801S which looks like a ceramic cap? CM806. ZD803 and ZD804, are those zener diodes? Can those be tested in circuit?

The board for this TV is $60-$90 otherwise I would just swap the board.

[diif]

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

STR-W6252 is a MOSFET and PWM controller in a single package.
I quickly test most components in circuit and if there is and dubious readings I remove and test again.
Yes they are zener diodes.
What's the cap the other side of the heatsink ?

[lucidbarrier]

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

STR-W6252 is a MOSFET and PWM controller in a single package.
I quickly test most components in circuit and if there is and dubious readings I remove and test again.
Yes they are zener diodes.
What's the cap the other side of the heatsink ?

It's the CM808 that I couldn't find. It's a Sam Young too. It looks like the 2 Zener Diodes are there too. Can I test the ZDs in circuit? I think diodes are continuous in one direction but not in the other?

Edit: The other caps "look" ok, but if I do get the parts for this thing, those NXB caps are going too.

Thanks for the help!

[diif]

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

You're welcome.
I remember doing the same board or similar a while back.
Diodes test with diode mode on your multimeter, leads one way then the other.
There are a couple of threads on here with that board, maybe worth checking to see which caps they replaced.

[lucidbarrier]

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

So I ordered a replacement power board on Ebay and it took ages to get here. It is the same part number but a different revision. The cable going from the power board to the main board on my TV is has two rows of wires in going to the connectors. The replacement board only has a single row. I reused the existing connectors from my TV. I checked both boards and they have the same pin out at the connector.

I installed the board, and the red standby light is lit up. When I press power on the remote, the standby led in the front blinks and I hear a chime from the speakers as it boots up. No picture, no backlight, only a red glow from the led on the main board. I took a flashlight and shined it on the screen and nothing. I pressed the menu button and there are no graphics or words anywhere.

So I took out my meter and probed the power connector.

Connector ---------Label --------- Reading ------ TV on/off
-----------------------------------------------------------------
Pin 3 --------- STBY 5.3V -------- 5.12v off / 5.09 on
Pin 7,8 --------- 13V (S) --------- 12.7v ----- ON
Pin 23 --------- INV ON/OFF ------ 0.00v
Pin 13,14,15,16 --- 5.3v ---------- 5.07v ----- ON
Pin 19,21,22 ------- 13v(m) ------ 12.7v ----- ON
Pin 27 --------- DET 5V ---------- .386v ----- ON
-----------------------------------------------------------------

The one that pops out at me is the Pin 23 which I assume is Inverter on/off.
So if I have this right, the power supply energizes the main board, the main board sends a reference signal back to the PSU to power the inverter that powers up the backlights?

Is there a way to force the backlights on? This board has the inverter integrated with the power supply. As I was looking over the replacement board, I noticed that the IC in 801S has a burn spot underneath as if it had previously failed but that has been replaced.

[R_J]

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

If you disconnect the cable going to the main board and plug in the tv, do the backlights come on?

[lucidbarrier]

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

If you disconnect the cable going to the main board and plug in the tv, do the backlights come on?

It acts like a dead set. No standby light, no chimes, just a black screen. I measured the standby voltage to see if I might have popped a fuse, but the standby voltage is still there. I plugged the connector to the main board back in and the standby light comes back on.

[budm]

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

I do not see Pin1 (ON/OFF (PS-ON).

[lucidbarrier]

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

I do not see Pin1 (ON/OFF (PS-ON).

I guess I forgot that one

Pin 1 = 1.163v (tv on) and 0v (tv Off)

[lucidbarrier]

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

So if I put a jumper across the 5.3V rail across to INV ON and PS ON, will the backlights come on?

[budm]

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

When forcing on the BL-ON or PS-ON, you must remove the wires going back to the main board first because you can damage the switched Transistors on the main board. You should also use resistor (470 Ohms ~1000 Ohms, one resistor per each forced on pin)) to connect between the standby 5V and the pin you are trying to force on in case you slip or jump the wrong pins.

[R_J]

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

This power supply does use 10k pull up resistors from 5 volts for power on/off & inverter on/off so with the main board plug disconected, measure the voltage at CNM802 pin (1) and pin (23) to see if it is being pulled up
You measured 13 volts on cnm802 pins 7,8,19,21,22 which seems to indicate that part of power supply is on.

[lucidbarrier]

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

When forcing on the BL-ON or PS-ON, you must remove the wires going back to the main board first because you can damage the switched Transistors on the main board. You should also use resistor (470 Ohms ~1000 Ohms, one resistor per each forced on pin)) to connect between the standby 5V and the pin you are trying to force on in case you slip or jump the wrong pins.

I'm not sure I was doing that right. I put a 1k ohm between STANDBY and PS ON and a 1K between a 5.3v rail and INV on, but there's no power going to the infrared module/power button if the main logic board is disconnected.

So I plugged it back in. Pulled the cover off the T-CONN and checked the continuity of the fuse. It was good. There seems to be voltages present on the pads next to the LVDS cable exiting the main board to the T-CONN. So I pulled one of the ribbon cables from the T-CONN going to the LCD and left the other side plugged in.

I turned the set on, again chimes but no video, no visible backlights. But this time when I shined a flashlight on the screen, there was a visible divide between the two sides of the screen right down the middle. Half the screen was black, and half a slightly greyish tint. Ever so slight, I almost missed it. I plugged in the ribbon cable and removed the cable on the other side of the T-CONN and the same thing but on opposite sides now.

I've included a picture but I don't know if you can see it, it's really faint. There are no visible wires going to the LCD panel from the inverter. I'm not really sure how the backlights get power.

[budm]

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

No need to use resistor, if the power supply/inverter board is good, the backlights should come on when you power up the power supply board without the cable to the main board is in place, it already has pull-up resistors for self testing the power supply/inverter board.

[lucidbarrier]

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

I was taking the boards off to take pictures and I flipped the main board over and there's a whole mess of corrosion on the back.

[budm]

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

No clean flux.
http://www.circuitnet.com/experts/56589.html
So did you run the self test of that power supply/inverter board to see if the backlights come on and stay on the minute you plug the power cord into the outlet?

[lucidbarrier]

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

No clean flux.
http://www.circuitnet.com/experts/56589.html
So did you run the self test of that power supply/inverter board to see if the backlights come on and stay on the minute you plug the power cord into the outlet?

Ok maybe I wasn't understanding this before but i think I got it now. I disconnected the cable right at the main board and stuck the resistor in there.

When I jump a 1k Ohm resistor across Pin 1 (PS ON) and Pin 3 (standby 5.3v)
and plug the power cable into the power supply, I get these readings:

Pin 1 = 1.5v
Pin 3 = 5v

Pin 23 = 5v (INV ON/OFF)

The screen is completely black. So the Inverter should be on at this point since there is 5v there right?

[budm]

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

No need for any resistors, the board already has built-in resistors for doing the self test, all you have to do is to disconnected the cable from the power supply board to the main board then plug the power cord into the outlet. if the power supply board is good then the backlights should come on and stay on, that is.

[lucidbarrier]

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

No need for any resistors, the board already has built-in resistors for doing the self test, all you have to do is to disconnected the cable from the power supply board to the main board then plug the power cord into the outlet. if the power supply board is good then the backlights should come on and stay on, that is.

Well, I unplugged the resistor and plugged the power cord back in. Either way, no backlights and it's completely black. Not even a flicker for one second.

Pin 1 = .8v
Pin 3 = 5v
Pin 23 = 5v

So either it's the inverter or the backlight bulbs are burnt out?

[budm]

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.