UN55D6900 BN44-00428B partial led driver circuit failure

[Daveleone]

Re: UN55D6900 BN44-00428B partial led driver circuit failure

I was trying to help but those hookups for the LED's just don't make any sense. I have a UN60D6000 (Man Feb 2012) opened and it is crystal clear. There are 8 LED segments, 4 left and 4 right each measuring about 143VDC with LED tester. Each pin has a wire as depicted in the legend on the board - see attached.

How were you testing with the LED tester - between what pins? How can you test L1, L2 when L1+ (5) has no wire and L2- (3) has no wire?

And I got nowhere trying to relate all those wires to the schematic that is in the thread you referenced - there just are not enough wires on that drawing for CNL801A & B.

Maybe I am just confused

Ok, I did a bunch of testing with my LED tester and my multimeter to check continuity, and here's what I figured out. All 4 LED driver circuits are the same, and the full circuits look like this:

1) R1+ to L1-
2) R3+ to L3-
3) R5+ to L5-
4) R7+ to L7-

Here's how the circuits work...
- There are 2 LED strips in the TV, a left one and a right one.
- Each LED strip has 4 segments.
- The segments on the left strip are: L2+ to L1-, L4+ to L3-, L6+ to L5-, and L8+ to L7-
- The segments on the right strip are: R1+ to R2-, R3+ to R4-, R5+ to R6-, and R7+ to R8-
- Testing between any single segment (eg L2+ to L1-, or R1+ to R2-) with the LED tester lights up the corresponding segment of LEDs on that particular strip and drives 69v.
- Testing for continuity shows that the Left and Right strips are tied together at the following points: R2- and L2+, R4- and L4+, R6- and L6+, and R8- and L8+
- Therefore, this creates 4 full LED driver circuits. For example, R1+ -> (R2-/L2+) -> L1- (so the full circuit is R1+ to L1-)
- Connecting the positive lead of my LED tester to R1+ and the negative lead to L1- lights up the corresponding 1st segment of LEDs on both the left and right strips and drives 138v across them.

Make sense? If it's still confusing let me know and I can draw a picture of it.

[RDC55]

Re: UN55D6900 BN44-00428B partial led driver circuit failure

bump. help needed, please

I was trying to help but those hookups for the LED's just don't make any sense. I have a UN60D6000 (Man Feb 2012) opened and it is crystal clear. There are 8 LED segments, 4 left and 4 right each measuring about 143VDC with LED tester. Each pin has a wire as depicted in the legend on the board - see attached.

How were you testing with the LED tester - between what pins? How can you test L1, L2 when L1+ (5) has no wire and L2- (3) has no wire?

And I got nowhere trying to relate all those wires to the schematic that is in the thread you referenced - there just are not enough wires on that drawing for CNL801A & B.

Maybe I am just confused

[Daveleone]

Re: UN55D6900 BN44-00428B partial led driver circuit failure

I would not rule out bad LEDs

Ok, thanks! In that case I think my next test will be to swap the wires in the connector so that the suspect LED driver circuit is driving a different subset of LEDs. If the original subset of LEDs are still not lit (the new driver circuit being used now appears affected/lower voltage) then the problem is the LEDs. If the problem moves to the new subset of LEDs then the problem is the original LED driver circuit.

I will report back my findings.

[neilc6]

Re: UN55D6900 BN44-00428B partial led driver circuit failure

I would not rule out bad LEDs. Your LED tester only puts out 10-20mA and the circuit likely runs at several hundred mA. I have replaced LEDs on a few models with symptoms of bad backlights but all the LEDs tested good with a tester (LG UH series with logo flash & Sony with 6 blinks). I've done so many that I typically don't even test any more and just replace them all with new.

[Daveleone]

Re: UN55D6900 BN44-00428B partial led driver circuit failure

bump. help needed, please

[Daveleone]

Hello TV experts! I have a UN55D6900. The successfully TV turns on, and the backlights light up, and I get a picture, but there is a section that is dim. I took it apart and 1 out of 4 segments of backlight LEDs are not lighting on both sides of the TV (in other words, the same segment is out on both LED strips).

I tested the LED strips with my LED tester and all of the LEDs light properly, so I believe the problem is with the PSU/LED driver board (BN44-00428B). The voltages at CNM810 (between PSU and main board) look ok to me. The voltages at CNL801A and CNL801B look off for one of the 4 LED driver circuits. I've bolded the voltages below that seem wrong to me.

CNM810
PWM_DIM4 0.265v
PWM_DIM3 0.265v
PWM_DIM2 0.265v
PWM_DIM1 0.265v
B13V 12.75v
BLU-ON 4.71v
GND 0
GND 0
ASV 5.40v
PS-ON 3.3v
NC 0
---------------------
OD_Level 3.253v
OD_ON 3.278v
GND 0
B13V 12.75v
B13V 12.75v
Vamp 1.789v
Vamp 1.789v
GND 0
B5V 5.39v
B5V 5.39v
NC 0

CNL801A
L2+ 99.7v
L6+ 101.3v
L1- 40.8v
L5- 42.1v
L8+ 100.8v
L4+ 68.0v ???
L7- 41.6v
L3- 14.69v ???
IF1 2.97v
IF2 2.97v

CNL801B
R7+ 161.8v
R3+ 126.8v
R8- 100.8v
R4- 68.0v
R1+ 160.8v
R5+ 162.3v
R2- 99.8v
R6- 101.3v

I also checked the voltages on either side of each diode in the 4 LED driver circuits (top voltage, bottom voltage)

D9451 161.6v / 126.8v
D9351 162.0v / 126.8v
D9251 126.8v / 126.8v (I think this driver circuit is bad)
D9151 160.5v / 126.8v

I've included images of both the front and the back of the LED driver circuits on the board. Looking for help on what I should test next to pinpoint what part of the driver circuit is bad and which component(s) need to be replaced?

THANKS!!

P.S. I did find this thread, but it focused on relay clicking/lack of power on, not faulty driver circuits. There are some schematics in there though.