Hi all! I have an LG 42LG50 that, when plugged in, shows a flashing red LED on the front, then the backlight flashes for a brief moment, then the front LED turns a very dim blue. (similar to this thread: https://www.badcaps.net/forum/showthread.php?t=52947)
Here are the connector pinouts with [expected voltage when on]:
P201
(left pins)
23 N/C
21 BR1 [1.7v]
19 PWR_ON [2.8v]
17 ERROR [0v]
15
13
11 [5.1v]
09 [5.1v]
07
05 [12.3v]
03
01 [16.5v]
(right pins)
24 N/C
22 PWM_DIM [1.4v]
20 ON/OFF [3.2v]
18 ACD [5v]
16 GND
14 GND
12 5V [5.1v]
10 5V [5.1v]
08 GND
06 12V [12.3v]
04 GND
02 16.5V [16.5v]
P204
01 24v
02 24v
03 24v
04 24v
05 24v
06 0v
07 0v
08 0v
09 0v
10 0v
11 BR1 [1.7v]
12 ON/OFF [3.2v]
13 PWM_DIM [1.4v]
14 ERROR [0v]
P205
01 24v
02 24v
03 24v
04 24v
05 24v
06 0v
07 0v
08 0v
09 0v
10 0v
11 BR1 [1.7v]
12 ON/OFF [3.2v]
I've checked the voltages at the power supply during power on, during the time when the backlight flashes, and after the backlight flash. As a convention, if I've listed a single voltage, that means that voltage is stable throughout the startup process. If I list multiple voltages it means the voltage changes during the cycle, with the format Vpower on->Vbacklight flash->Vafter backlight flash. I've underlined the values I think are suspect.
P201 (top to bottom)
(left pins)
23 0v
21 0v->1.87v (but quickly drops to 0.66v)->3.3v
19 2.8v
17 0v->0v->3.3v
15 0v
13 0v
11 5.2v
09 5.2v
07 0v
05 12.5v
03 0v
01 16.1v
(right pins)
24 0v
22 0v
20 3.4v->1.7v->3.4v
18 5.0v
16 0v
12 5.2v
10 5.2v
08 0v
06 12.5v
04 0v
02 16.1v
P204 (left to right)
01 24.8v
02 24.8v
03 24.8v
04 24.8v
05 24.8v
06 0v
07 0v
08 0v
09 0v
10 0v
11 0v->1.6v (but quickly drops to 0.66v)->3.3v
12 3.3v->1.7v->3.3v
13 0v
14 0v->0v->3.3v
P205 (top to bottom)
01 24.8v
02 24.8v
03 24.8v
04 24.8v
05 24.8v
06 0v
07 0v
08 0v
09 0v
10 0v
11 0v->1.8v (but quickly drops to 0.66v)->3.3v
12 3.3v->1.7v->3.4v
My thoughts and questions...
What would you recommend as next steps in hunting down the source of the ERROR? As always, your help is greatly appreciated!
Thanks,
--Dave
Here are the connector pinouts with [expected voltage when on]:
P201
(left pins)
23 N/C
21 BR1 [1.7v]
19 PWR_ON [2.8v]
17 ERROR [0v]
15
13
11 [5.1v]
09 [5.1v]
07
05 [12.3v]
03
01 [16.5v]
(right pins)
24 N/C
22 PWM_DIM [1.4v]
20 ON/OFF [3.2v]
18 ACD [5v]
16 GND
14 GND
12 5V [5.1v]
10 5V [5.1v]
08 GND
06 12V [12.3v]
04 GND
02 16.5V [16.5v]
P204
01 24v
02 24v
03 24v
04 24v
05 24v
06 0v
07 0v
08 0v
09 0v
10 0v
11 BR1 [1.7v]
12 ON/OFF [3.2v]
13 PWM_DIM [1.4v]
14 ERROR [0v]
P205
01 24v
02 24v
03 24v
04 24v
05 24v
06 0v
07 0v
08 0v
09 0v
10 0v
11 BR1 [1.7v]
12 ON/OFF [3.2v]
I've checked the voltages at the power supply during power on, during the time when the backlight flashes, and after the backlight flash. As a convention, if I've listed a single voltage, that means that voltage is stable throughout the startup process. If I list multiple voltages it means the voltage changes during the cycle, with the format Vpower on->Vbacklight flash->Vafter backlight flash. I've underlined the values I think are suspect.
P201 (top to bottom)
(left pins)
23 0v
21 0v->1.87v (but quickly drops to 0.66v)->3.3v
19 2.8v
17 0v->0v->3.3v
15 0v
13 0v
11 5.2v
09 5.2v
07 0v
05 12.5v
03 0v
01 16.1v
(right pins)
24 0v
22 0v
20 3.4v->1.7v->3.4v
18 5.0v
16 0v
12 5.2v
10 5.2v
08 0v
06 12.5v
04 0v
02 16.1v
P204 (left to right)
01 24.8v
02 24.8v
03 24.8v
04 24.8v
05 24.8v
06 0v
07 0v
08 0v
09 0v
10 0v
11 0v->1.6v (but quickly drops to 0.66v)->3.3v
12 3.3v->1.7v->3.3v
13 0v
14 0v->0v->3.3v
P205 (top to bottom)
01 24.8v
02 24.8v
03 24.8v
04 24.8v
05 24.8v
06 0v
07 0v
08 0v
09 0v
10 0v
11 0v->1.8v (but quickly drops to 0.66v)->3.3v
12 3.3v->1.7v->3.4v
My thoughts and questions...
- Based on the stable voltages at P201 pins 2,4,10,12, and 18, and at P204/205 pins 1-5, I think the power supply is ok.
- I took apart the panel and was able to see all of the CFL tubes light up momentarily, so the CFL tubes themselves seem ok. (I've attached a 2 jpg sequence of the bulbs powering up)
- Obviously, the 3.3v on ERROR (P201 pin 17, P204 pin 14) means something went wrong.
- Why does BR1 (P201 pin 21, P204 pin 11, P205 pin 11) go to 1.7v, then drop to 0.66v, and finally become stable at 3.3v (expected stable value is 1.7v)?
- Why does PWM_DIM (P201 pin 22, P204 pin 13) remain 0v? Why does it never rise to the expected 1.4v?
- Why does ON/OFF (P201 pin 20, P204 pin 12, P205 pin 12) go to 3.4v, then drop to 1.7v, then go back to 3.4v (expected stable value is 3.4v, so maybe that's ok since it is eventually stable at 3.4v)?
- How to figure out if the problem is the main board, the t-con, the CFL driver/ballast boards, or the LCD panel itself?
What would you recommend as next steps in hunting down the source of the ERROR? As always, your help is greatly appreciated!
Thanks,
--Dave
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