42LN5300 no stand by light.

[hanswr]

After taking a hard self confidence hit in my last attempt to repair a TV here I come again trying to feel productive during these unemployed and uncertain times.

I have a 42 inch LG Led TV model 42LN5300.

Symptoms:
- No red stand by light.
- No image, no sound.
- Won't turn on at all.

Please see attached images. I have added the voltage readings I get in the P201 connector.

By reading an unsuccessful attempt of a repair from another user, one of the things you asked to check was the voltage on Q201 the voltage there is 35v on left and right leg.

Thank you in advanced for any help provided on what to test next. I would like to repair this TV spending the less $ possible. I know there are tons of power and main boards on eBay but I cannot afford that at the moment.

[tvtimmy]

Re: 42LN5300 no stand by light.

I believe it's the mainboard. I think you can sub any LN model mainboard (32"-50").

[nomoresonys]

Re: 42LN5300 no stand by light.

Easy test to try, with tv UNPLUGGED, test all the diodes on powerboard, meter set to diode mode, with a probe on each leg of diode, should get a reading around .3xx to around .7xx in one direction then reverse the probes should read 1 or OL if you get voltage in both directions or none at all investigate it further, if any read off de-solder or clip a leg and retest out of circuit, sometimes you will get an off reading because of other things on the circuit.

[dick_barton]

Re: 42LN5300 no stand by light.

Disconnect the mainboard from the power supply and using a 1K resistor, jump PWR_ On to the 3.5V pin and then check your other voltages?

Edit
Is R103 burnt or is it black marker pen and is D105 broken?

[dick_barton]

Re: 42LN5300 no stand by light.

If that brings up your power supply then you could also use another 1K resistor from 3.5V to DRV_ON to bring up the backlights

[hanswr]

Re: 42LN5300 no stand by light.

I believe it's the mainboard. I think you can sub any LN model mainboard (32"-50").

The problem is in fact related to the main board, thank you!. I did not know you could substitute from another LN model despite being different size.

I replaced the main board from an old 32" LN model and the TV works, all voltages reading are there in the correct ranges as printed on the board.

Disconnect the mainboard from the power supply and using a 1K resistor, jump PWR_ On to the 3.5V pin and then check your other voltages?

Edit
Is R103 burnt or is it black marker pen and is D105 broken?

Thank you for this suggestion! It will certainly come handy when testing other power boards.

R103 and D105 are good, just bad picture quality, I apologize.

Is this main board problem something that can be repaired?

[yokoono]

Re: 42LN5300 no stand by light.

Try a reflow to the processor.