Samsung LN40D550 Dim Right Half

[neilc6]

I fixed a TV with this issue before that had a blown fuse and bad caps on a slave inverter board. Think this is a different setup with a balancer board.

Power supply looks clean with no bulged caps.

Balancer board input voltages
1 High (FET) pink - Not sure how to measure (expected voltage?)
2 NC
3 Low (FET) white - same as pin 1
4-7 NC
8 GND 0V
9 OVP 0V
10 CNT_PRT 12.1V DC
11 VCC 12.8V DC
12 LD 11.36V DC

[budm]

Re: Samsung LN40D550 Dim Right Half

What is the P/N of the power supply board? BN44-????
The board connected to the lamps is not Balancer, it is Inverter board, but instead of using 24VDC and the related power MOSFETs mounted on the inverter board to drive the inverter transformer, the drive circuit for the primary windings of the inverter transformer is on the power supply board through that HIGH/LOW pins.

[ReeceyBurger123]

Re: Samsung LN40D550 Dim Right Half

Ive had the uk model of this fail in the same way, Lcd panel was toast backlight fine.

[budm]

Re: Samsung LN40D550 Dim Right Half

I guess he can disconnect the cable to the TCON and see if the screen will glow evenly or not.

[neilc6]

Re: Samsung LN40D550 Dim Right Half

Sticker on the power supply board says CN08BN440440440ASE38BBMI062.

I disconnected the TCON and it doesn't power up when I do that. I read you can cause damage disconnecting the TCON with it powered up.

From the back, the backlight is dimmer on the dark half. Brightness controls don't do anything.

[budm]

Re: Samsung LN40D550 Dim Right Half

So it is BN44- 00440A.
Disconnecting the TCON from the main board will not cause the damage, if the TCON has an error signal to feed the main board, then the TV will not start up, some TVs do not use the error signal from the the TCON so the TV will still come on but without showing images on the screen.

[neilc6]

Re: Samsung LN40D550 Dim Right Half

Ok disconnected TCON with tv running and right side is still dim. Anything else to try?

Edit add: I searched that PS board number BN44-00440A in this forum and there are a few threads showing potentially bad caps on the PS. I will research a bit more and report my resolution.

[budm]

Re: Samsung LN40D550 Dim Right Half

CI1826, check its capacitance.
Also verify that you have close to 400VDC between the two legs of the main filter (the large 450VDC caps laying on the side).

[neilc6]

Re: Samsung LN40D550 Dim Right Half

Looks like my board is like this thread https://www.badcaps.net/forum/showth...ht=BN44-00440A

I measure 160VDC across each of the big caps same as the OP in the other thread.

I pulled off CP811, put it in my ESR tester and it detects as a 0 ohm resistor. I will order the part and report back.

Is CI1826 a usual suspect also?

[budm]

Re: Samsung LN40D550 Dim Right Half

If all you get is 160vdc on the main filter caps then the PFC Voltage booster is not working so the inverter circuit is not getting the full Voltage to produce full output.
As you can see in that thread, we found bad cap that has leakage resistance of around 300 Ohms, so you need to read that thread and test the suspect cap.

[neilc6]

Re: Samsung LN40D550 Dim Right Half

Just replaced CP811 with a 220pf/3kV and backlight is at full brightness. Thanks budm and browserjoe who did all the legwork in the other thread pinpointing the failed part.

[segasonicfan]

Re: Samsung LN40D550 Dim Right Half

nice! a cool fix to try in future projects. congrats!

[budm]

Re: Samsung LN40D550 Dim Right Half

Thanks for the follow-up of the repair.

[funnel]

Re: Samsung LN40D550 Dim Right Half

Just replaced CP811 with a 220pf/3kV and the right half of my screen returned to full brightness.

Some more details regarding my situation:

1. Right half of my LN40D550 TV went dim immediately without warning.
2. I turned power off and then back on and heard a 'pop' sound.
3. TV continued to function with right half of screen dim.
4. I opened TV and observed CP811 had a crack on its casing (I imagine this crack occurred when I heard the 'pop' sound).
4. I touched CP811 and then decided to turn back on TV one last time before replacing CP811.
5. After TV was turned back on, smoke starting coming out of transformer TM801S.
6. I replaced CP811 which fixed the problem with the dim right half of the screen and it also stopped smoke from coming out of TM801S.

I figured I would share this additional information in case it will help someone.