LG 42LG50FD-AD Intermittent NoGo

[con244]

Re: LG 42LG50FD-AD Intermittent NoGo

Well all seems good. The tv has been testing for a couple of days now and is yet to falter again. Thanks to everyone who offered help.
Cheers
Con

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

Same problem with this set.
I have 1x 5v voltage, no ps-on voltage tv came cold to me.
they had it working for 5 days and it failed.

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

Recapped the entire board.
I have voltages there now.

NC | 0
PWM-DIM | 1.361V
ON / OFF | 2.972V
PS-on | 3.182v added for budm
ACD | 0
grd
grd
5v | 5.150v
5v | 5.150v
grd
12v | 0
grd
16v - 5v | 0

I am not getting inverter power at all, there is no 24v at the power inverter fuse.

[budm]

Re: LG 42LG50FD-AD Intermittent NoGo

Where is the Voltage reading of the Power_On (PS-ON signal from main board) pin to turn the rest of the power supply? Still 0V?

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

There is no pin connector for ps-on on this board not that I can find anyway.

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

Just looked at schematic should of known it wasn't labelled on the board.
PS-on | 3.182v

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

Just made sure all caps where put in their right destinations.
This has me stumped I am not sure where to go from here.

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

with the inverter plugged pulled the PS-on reads 5.0v is this normal?

[budm]

Re: LG 42LG50FD-AD Intermittent NoGo

Recapped the entire board.
I have voltages there now.

NC | 0
PWM-DIM | 1.361V
ON / OFF | 2.972V
PS-on | 3.182v added for budm
ACD | 0
grd
grd
5v | 5.150v
5v | 5.150v
grd
12v | 0
grd
16v - 5v | 0

I am not getting inverter power at all, there is no 24v at the power inverter fuse.

So based on your readings, you have PS-ON but you still do not have the 12V, 16V, or 24v.
We need to find out if you do have PFC Boosted Voltage of around 380VDC between the two legs of the main filter cap or not, if you do then we need to find out if that boosted Voltage gets all the way to the rest of the SMPS power supply to produce the 12V, 16V, and 24V circuit or not. We need to have the correct main power supply Voltage first.
BTW, that ACD (that AC Detect) signal is 0 VDC, I expect it to be >2V for normal working but I am not sure if 0VDC = NORMAL or >2VDC = Normal.

[vinceroger69]

Re: LG 42LG50FD-AD Intermittent NoGo

what is the psu board number

[dskall]

Re: LG 42LG50FD-AD Intermittent NoGo

Budm can correct me. ACD 0 usually needs voltage on that pin or won't start up. NVM

[budm]

Re: LG 42LG50FD-AD Intermittent NoGo

I believe the ACD is part of the protection circuit that will stop the power supply from coming on if the incoming AC is not in the operating range. In SONY TV, the ACD (AC OK) = > 2V = GOOD, I do not know if LG uses active low or active high. That signal is sent to the main board and usually will shut down the PS-ON signal, but in this case the PS-ON is present. The topology may not be the same as SONY but I cannot verify 100% since we do not have the diagram of the power supply board.
So at this point he needs to at least verify that the PFC is working or not which is easy enough to check.

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

Main filter cap reads 326.1v - 328.3v

I suspect the PFC boosted voltage is not up to its correct running voltage.
I soldered some wires to main filter cap + - and alligator clipped them as I thought it was safer, hope I have done this right.

Vinceroger69 the PSU board is a Eax40157601/17

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

did another test on the Main filter Cap just to be sure.
Its reading 322.6v pretty sure its reading low just reading some other threads similar to get a grasp on what might be happening.

[Ian Paul]

Re: LG 42LG50FD-AD Intermittent NoGo

This may be the diagram for this board:-
https://electronicshelponline.blogsp...?view=snapshot

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

That's the diagram I used to make sure I hadn't used the wrong caps. I was eventually going to link us there.
Text isn't all that great when zoomed in but its a good reference.

[budm]

Re: LG 42LG50FD-AD Intermittent NoGo

Main filter cap reads 326.1v - 328.3v

I suspect the PFC boosted voltage is not up to its correct running voltage.
I soldered some wires to main filter cap + - and alligator clipped them as I thought it was safer, hope I have done this right.

Vinceroger69 the PSU board is a Eax40157601/17

So the PFC Voltage booster is not working.
1) It can be due to bad PFC diodes
2) No VCC present to run the PFC IC
3) Failed PFC IC.

[vinceroger69]

Re: LG 42LG50FD-AD Intermittent NoGo

have you got a picture of the bottom of the psu pcb maybe then we can help you locate the pfc ic so that you can check all the voltages etc

[Amraks]

Re: LG 42LG50FD-AD Intermittent NoGo

Is it safe to test the VCC line off that chip soldering a wire to the positive side of C508 and using the chassis as ground. as VCC line of that chip goes straight to the C508 + and D508. stop me if I am wrong I will not move ahead until I have confirmation.
I checked the diodes on the PFC circuit pulled out D508 as he was reading both ways in circuit tested fine out of circuit.

I am using that schematic its been handy so far.

[budm]

Re: LG 42LG50FD-AD Intermittent NoGo

You will be making Voltage measurement in the hot deadly side of the circuit. The GND ref for the hot side is the negative leg of the main filter, not the chassis.
You should at least plug the TV into the GFCI out at the minimum to protect yourself.