LG 50pq3000

[bill25]

After a power outage, my lg plasma tv fails to start. When i try to start up the TV, clicking sound comes from psu and the Red light desapears. After a minute the red light is back on. No sound no image nothing.I checked all voltages on the secondary of power suplly and only 5 volts stby is correct. I checked some parts like power mosfets, diodes, zeners. fuses, resistor, etc.On the first side of psu 300v on big caps is on. If you can help i would appreciated. Thanks!

[R_J]

Re: LG 50pq3000

use the "Search" feature in this forum and enter your model number, there are lots of threads that might be helpful.

[bill25]

Re: LG 50pq3000

I checked all the posts already. Nothing helpful

[R_J]

Re: LG 50pq3000

Try disconnecting VS supply from the Y-sus and Z-sus and see if the voltage comes up on the power supply side. If there is a short on either board the power supply will go into over current shutdown.

[bill25]

Re: LG 50pq3000

I tested the psu with the motherboard only and the problem its the same no voltages.I changed the motherboard with another and nothing happens I suspect the psu because of the AC power outage for a few second. I am electronic tech. here in my country but my knowledge its not good with plasma tv's. I understand the logic of all the bords but i dont have the experience, because i fixed plasma's only 2 or 3 times. Thanks.

[Biruslapio]

Re: LG 50pq3000

The power supply should auto start on AC power only, with all other cables disconnected from it (YSUS and motherboard), VS, VA and all other voltages should come up, if they don't, power supply is faulty.

[bill25]

Re: LG 50pq3000

Ac voltages 220v , bridge +300v DC on the first part of psu its ok. Second Part cables to motherboard only 5 volt stby is stable and cables VS, VA to YSUS have no volts. I believe PSU without the mainboard is not start to fix all the other voltages. I understand from the begining that the problem is the PSU and check almost all important parts on it, with no luck. So is someone who have the same problem with me or any idea how to fix it?
Thanks.

[Biruslapio]

Re: LG 50pq3000

You should have 5V on AUTO_GND pin on the connector that goes to mainboard, with all cables disconnected except AC.

No relays clicking?

Post a photo of your power supply front and back sides.

[R_J]

Re: LG 50pq3000

Check that the fuse F801 is ok

[bill25]

Re: LG 50pq3000

Biruslapio please check symptom on my first post. 5 volt is on, relay clicking, Red light desapear, no sound no image, and after a minute Red light is back again.Without mainboard relays not clicking.

RJ all fuses are OK.

[R_J]

Re: LG 50pq3000

You should be able to check the power supply on the bench with just ac mains connected. You can use a 1k resistor between STBY5V and RL_ON, this should give you at least the 12V. If this works you can turn on the VS with another resistor between STBY5V and VS_ON, this should give you the VS voltage, but wiyhout a load it might come up and drop back down.

[ReeceyBurger123]

Re: LG 50pq3000

Watch my video, sounds like the MB has BGA solder issues and is failing intermittently. Force a power up first to check.

[bill25]

Re: LG 50pq3000

The mainboard is changed with another one with no effect. I try tomorow to start the psu with the resistors and see what happens. Thanks for your advices.

[bill25]

Re: LG 50pq3000

The results from the bypass with resistors is the same. No dc power on the mainboard and VA, VS connectors. I believe that the big IC with 28 pins is not working properly

[bill25]

Re: LG 50pq3000

[dick_barton]

Re: LG 50pq3000

It looks like, but hard to read the number off your photo precisely, that it's an MC80F0704 micro

https://datasheetspdf.com/pdf-file/6...OR/MC80F0704/1

[bill25]

Re: LG 50pq3000

Its the mc80f0708-09fd.

[dick_barton]

Re: LG 50pq3000

What voltage do you have on Pin 5. Does it match what's given in the data sheet?

[bill25]

Re: LG 50pq3000

I think is 5.1 volt after a fast search for voltages on the IC but i will check tomorrow for sure.

[R_J]

Re: LG 50pq3000

Check if the main DC voltage on F801 changes from the 300 volts to around 385 volts when you connect STBY5V and RL_ON with the 1k. You can use one of the heat sinks in the primary for hot ground. Also do you here the relay click when you do this test?
Thanks for the picture, I was looking at a different power supply before.