LG 50PK550-UD.AUSALHR (No picture, No Sound)

[SdlewisSr]

Hi everyone

I have an LG 50PK550-UD.AUSALHR that has standby, but does not power up (no picture, no sound). When plugged in the power supply clicks 4 (2 then 1 then 1) times. D1 on the contol board is not blinking.
In standby mode the power supply (PSU PN: EAY60968801) on P813 (to main board) there are the following three voltages.
P813 (to main board)
Pin#
1 (17v):
2 (GND):
3 (5.1v): .463 volts
4 (5.1v ERROR DET): .463 volts
5 (GND):
6 (GND):
7 (STBY): 3.44 volts
8 (AC DET/RL_ON):
9 (AUTO_GND/M_ON):

When power button is pressed there are 2 clicks and these are the voltages on the PSU. (D1 on the contol board is not blinking.)

P813 (to main board)
Pin#
1 (17V): 17.15 volts
2 (GND):
3 (5.1V): 5.12 volts
4 (5.1V ERROR DET): 5.12 volts
5 (GND):
6 (GND):
7 (STBY): 5.08 volts
8 (AC DET/RL_ON): 2.43 volts
9 (AUTO_GND/M_ON): 3.28 volts

P812 (to YSUS)
Pin#
1 (VS): 202 volts (Panel says it should be 203 volts)
2 (VS): 202 volts (Panel says it should be 203 volts)
3 (NC):
4 (GND):
5 (GND):
6 (VA): 60 volts (Panel says it should be 60 volts)
7 (VA): 60 volts (Panel says it should be 60 volts)
8 (GND):
9 (M5V): 5.08 volts
10 (M5V): 5.08 volts

P811 (to ZSUS)
Pin#
1 (VS): 202 volts (Panel says it should be 203 volts)
2 (VS): 202 volts (Panel says it should be 203 volts)
3 (NC):
4 (GND):
5 (GND):
6 (NC):
7 (NC):
8 (GND):
9 (M5V): 5.1 volts
10 (M5V): 5.1 volts

Since D1 on the control board does not blink and the PSU voltages seem fine, I suspect the control board is the problem. Does anyone have any suggestions how to isolate the control board to see if it is causing the problem.

Thanks in advance for any help

[tvtimmy]

Re: LG 50PK550-UD.AUSALHR (No picture, No Sound)

Unplug LDVS cable at the control board and put a wire in the holes circled in red. Turn on tv and check for the test patterns. If you see them your mainboard is bad.t

[SdlewisSr]

Re: LG 50PK550-UD.AUSALHR (No picture, No Sound)

I disconnected the LVDS cable at the control board and put a wire in the holes and there was no change nor was there any test pattern.

[SdlewisSr]

Re: LG 50PK550-UD.AUSALHR (No picture, No Sound)

I checked the voltages on the control board and I have 18 volts and M5V coming into P1 and leaving on P2 (no voltages on the rest of P2's pins).
I have the correct voltages on IC103, IC22, IC23, IC53, FL1, FL2, FL5, X1, C57, C61, L1, L2, IC61, C76, IC51, C72, and C86. These are all on the front. I did not check those on the back of the control board (IC103, IC23, IC52).
Since D1 on the control board does not flash/blink, I still suspect the control board. However, I did not want to replace the control board until I check the YSUS board and ZSUS board. Since the voltage drop across the Z-Bias (R275) on the ZSUS board was only 14.8 volts and the panel says it should be 108 volts, I took the ZSUS board out of the TV and it powered up with sound, but no picture. When I hooked the cable to the TV I got sound from the TV show that was on. D1 on the control board still did not flash/blink.
I put the ZSUS board back into the TV, but did not connect the ZSUB board to it, the TV still powered up the same way it did without the ZSUS board.
Next I connected the ZSUB board back to the ZSUS board. When I powered it back up it still powered up with sound the way it did without the ZSUS and ZSUB boards. Go figure...
I still do not have a picture.
I disconnected the YSUS board from the PSU and still had sound but no picture.
I reconnected the YSUS board to the PSU and disconnected the YDRIVE Upper and Lower boards from the panel and still had sound, but no picture.
I reconnected the YDRIVE Upper and Lower boards to the panel and disconnected the YDRIVE Upper from the YSUS board and still had sound, but no picture.
I reconnected the YDRIVE Upper board to the YSUS board and disconnected the YDRIVE Lower board from the YSUS board and still had sound, but no picture.
I reconnected the YDRIVE Lower board to the YSUS board and still had sound, but no picture.
Now I am back to square one. Since D1 on the control board still does not flash/blink and there are no other voltages on P2 leading to the ZSUS board, except the 18 volts and M5V, I suspect it is the control board.
Does this make sense to anyone else?

[R_J]

Re: LG 50PK550-UD.AUSALHR (No picture, No Sound)

I have a training manual for a 50PK950 if you think it will help?
I am uploading it here. It looks to be very similar so it might help.

[SdlewisSr]

Re: LG 50PK550-UD.AUSALHR (No picture, No Sound)

Thanks!! R_J
I will take all the help I can get.
I looked for the one for this model and could not find it.

[NSchober]

Re: LG 50PK550-UD.AUSALHR (No picture, No Sound)

I have a service manual for LG 50PK550 from manualslib.com. I dont know if it covers LG 50PK550-UD.

[SdlewisSr]

Re: LG 50PK550-UD.AUSALHR (No picture, No Sound)

Thanks NSchober,
I have it also and it appears to only cover the -AA and not the -UD. The only schematics are of the main board and none of the control board. I ordered a control board and will see if it fixes the problem.

[SdlewisSr]

Re: LG 50PK550-UD.AUSALHR (No picture, No Sound)

Thanks everyone for your input. I replaced the control board and it's working just fine.