LG 70UH6350 Mainboard issue

[Storyteller12]

Originally Posted by dskall

So what voltages have you found?

1. 24v - 27v
2. 24v - 27
3. 24v - 27v
4. 24v - 27
5. G - 0
6. G. - 0
7. 12v - 11.77.
8. 12v - 11.77
9. G. - 0.
10. G. - 0
11. G - 0.
12. G. - 0
13. Pwr on - 2.8.
14. P-dim 2 - 0v
15. G. - 0.
16. 12v - 11.77
17. 12v - 11.77.
18. 12v - 11.77
19. 24v - 27.
20. 24v - 27
21. G. - 0.
22. G. - 0
23. DRV On - 0.
24. P-dim 1 - 2.96
25. G. - 0.
26 sclk - 0
27. Vsync - 0.
28. Sin - 0

[dskall]

You did ask for help on your mainboard. I gave you some voltages. But while we are on power board does your voltage change on Pwr on and DRV On when you press your power button?

[Storyteller12]

Originally Posted by dskall

You did ask for help on your mainboard. I gave you some voltages. But while we are on power board does your voltage change on Pwr on and DRV On when you press your power button?

Sorry I’m new to troubleshooting mainboards. Not sure where to check For those voltages you mentioned a few post back.

As for the pwr on and dvr on I’ll have to check tomorrow what they are in Standby. The ones I provided are after hitting the power button to turn on.

[dskall]

I think drv_on is your backlights. Probably should have a voltage if not in standby.

[Storyteller12]

That would make sense because the backlights don’t come on.

[dskall]

If you activate backlights I wonder if you would get a picture.

[Storyteller12]

Possibly, would it damage anything else doing that. There’s several smd caps that are shorted to ground. I just don’t want to cause more problems. But I can try….

[nomoresonys]

Try unplugging everything from the mainboard you are testing if you haven't already and see if you still have the shorts, lots of things can cause it, recently had a wire on the power to mainboard cable fried and it made many caps test short on mainboard when all boards were hooked up, need to track down the short if you have one, what procedure are you using when testing?

[Storyteller12]

Originally Posted by nomoresonys

Try unplugging everything from the mainboard you are testing if you haven't already and see if you still have the shorts, lots of things can cause it, recently had a wire on the power to mainboard cable fried and it made many caps test short on mainboard when all boards were hooked up, need to track down the short if you have one, what procedure are you using when testing?

I removed the main board from the tv. So nothing else hooked up. Then I started testing all the smd caps and found them shorted to ground along with an 8 pin ic which I removed and it tested fine out of circuit.

Haven’t started removing any bad caps yet to see if one of them failed and caused the short.

[nomoresonys]

And you still have the shorted caps with that IC removed?

[Storyteller12]

Originally Posted by nomoresonys

And you still have the shorted caps with that IC removed?

Yes, caps still shorted

[Diah]

my post#11

this is wrong way you walking on.. take out the powerboards on the table alone and just jumper STBY and Pwr on .. messures yours 24V it should 24 or little less not 27 as you wrote . any time you plug the MB with this PCB will toasted more.

[nomoresonys]

He has shorted caps on the mainboard with it unplugged from everything else.

[Storyteller12]

Originally Posted by Diah

my post#11

this is wrong way you walking on.. take out the powerboards on the table alone and just jumper STBY and Pwr on .. messures yours 24V it should 24 or little less not 27 as you wrote . any time you plug the MB with this PCB will toasted more.

I have 24v on the power supply when it’s powered on. But when I plug in the mainboard it jumps to 27v.

So it’s the main board that is the problem. Not the power supply. We have confirmed this.

Now I need to find out what is shorted on the main board causing all the smd caps to be shorted.

[Diah]

Originally Posted by Storyteller12

I have 24v on the power supply when it’s powered on. But when I plug in the mainboard it jumps to 27v. .

then good, 24V rail on MB used only for Audio amp / Tuner / and DC to DC 5V.

[Storyteller12]

Ok, we are making some progress. So what should I be testing or looking for now? Bad IC or do you think one of those smd caps is shorted causing everything else to be short

[Diah]

i dont think so.most caps will be mounted withhin chassis iif one short MB will cutoff pwr on.
each circuit i mentioned before working with 24V line. all took the feed via L . disconnect on side of this L or complete out and check 24 back to normal or not.

[Storyteller12]

Sorry, I’m not sure what you mean by Feed via L?

[Diah]

L = Coil you check which L had 27V mean its the line inter to the circuit we talked on. sure all the mentioned circuit will read 27 this why need to disconnect one by one and check if 24 back to normal

[Storyteller12]

Ok I understand now. Thanks for the clarification I will check when I get back to the office and let you know what I find.

Thanks again