LG50PA5500 will not turn on

[woodman45]

Hello everyone,this is my first post and questions i have on the forum so please bear with me if i make any mistakes..
I have read all the stickies and searched in threads pertaining to my model but could not find any info on the problem I am having.

The pics i have attached are of all the boards and if they are not clear enough i will attempt to get closer better ones.

I first thought i had a psu issue & replaced the c802 cap as i had read in other threads,but that didn't solve the problem.
I tested the voltages to video board and the bottom pin read 16.96 volts,the other 2 test pins read 5.2 volts all within the spec on the board.

Then i tested Va & Vs voltages they read nothing zero.
So i then unplugged power source waited 5-10 minutes unplugged connector to video board the powered tv on & the screen flashed on for 1-2 seconds & i could hear x & y boards humming.
So then i tested the Va voltage & it read 55v then tested Vs and it read 204 volts.
Just to note that with the video board connector plugged in to psu the red led on video board is on as well as the red led on the front of the tv power panel.

So is it possible that the video board is bad and causing the problem?
Any help or direction would greatly be appreciated.

[Andrew F. Ali]

Re: LG50PA5500 will not turn on

OK so you may have determined that the PSU Bd is good. But under load it may defect. First build a 'test load' for the Vs. Simply connect two (2) 220V 100W light bulbs in series, therefore you end up with 2 ends of wires to connect to the cct. If P-813 is the connector to the Main Bd, then there are two (2) rows of pins odd and even.
A. Disconnect ALL connectors to the PSU Bd
B. Ground the Auto_Gnd (pin22). Apply the AC and measure AC Det (pin18) and 5V StBy (pins 9-12) are 5Vdc. Remove AC after test.
C. Connect a 1kOhm resistor across 5V StBy (pin 9-12) to RL_ON (pin 19). [Closes relays to produce 17Vdc and 12Vdc.]
D. Connect another 1kOhm resistor across 5V StBy (pin 9-12) to M_ON (pin 21). [Produces a M5Vdc to P-811 connector pins 9&11 output stage]
E. Connect another 1kOhm resistor across 5V StBy (pin 9-12) to VS_ON (pin 20). { Produces on P-811 Vs voltage on pins 1&2 and Va voltage on pins 6&7]
F. Connect the 'test jig' across pin 1or2 and GND.
G. Apply AC and 'test jig' will come on. Leave it on for a bit and observe the brightness of the light bulbs. If it remains stable then for sure the PSU is OK. If not PSU Bd defective.
H. If 'test jig' remains stable then Main Bd defective.
NOTE: If the connector No. is not P-813 on your PSU Bd,you can still do this test. Just apply this method to the correct pin Nos. according to your set up.

[woodman45]

Re: LG50PA5500 will not turn on

OK so you may have determined that the PSU Bd is good. But under load it may defect. First build a 'test load' for the Vs. Simply connect two (2) 220V 100W light bulbs in series, therefore you end up with 2 ends of wires to connect to the cct. If P-813 is the connector to the Main Bd, then there are two (2) rows of pins odd and even.
A. Disconnect ALL connectors to the PSU Bd
B. Ground the Auto_Gnd (pin22). Apply the AC and measure AC Det (pin18) and 5V StBy (pins 9-12) are 5Vdc. Remove AC after test.
C. Connect a 1kOhm resistor across 5V StBy (pin 9-12) to RL_ON (pin 19). [Closes relays to produce 17Vdc and 12Vdc.]
D. Connect another 1kOhm resistor across 5V StBy (pin 9-12) to M_ON (pin 21). [Produces a M5Vdc to P-811 connector pins 9&11 output stage]
E. Connect another 1kOhm resistor across 5V StBy (pin 9-12) to VS_ON (pin 20). { Produces on P-811 Vs voltage on pins 1&2 and Va voltage on pins 6&7]
F. Connect the 'test jig' across pin 1or2 and GND.
G. Apply AC and 'test jig' will come on. Leave it on for a bit and observe the brightness of the light bulbs. If it remains stable then for sure the PSU is OK. If not PSU Bd defective.
H. If 'test jig' remains stable then Main Bd defective.
NOTE: If the connector No. is not P-813 on your PSU Bd,you can still do this test. Just apply this method to the correct pin Nos. according to your set up.

Thanks for the reply,I will get all the stuff together in the next few days and post back results & any questions I may have.
Very good info & greatly appreciated.

[Terryfictv]

Re: LG50PA5500 will not turn on

Check the most common failure first !
C802 open, visually bloated - 223J 1250v on PS board EAY62609701.

[woodman45]

Re: LG50PA5500 will not turn on

Check the most common failure first !
C802 open, visually bloated - 223J 1250v on PS board EAY62609701.

Yes I had read about that being a common problem with C802 & did replace it.
I checked the new one & old one with a capacitance meter & both read 22.1 nF out of circuit.

[woodman45]

Re: LG50PA5500 will not turn on

Just an update I replaced main video board and that was the problem.