LG 42ln5300-UB won’t turn on and only has standby voltage

[budm]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

Quote:
Originally Posted by R_J View Post
The board outputs for a (42") 157.5v/ 341ma I agree he has an open led string.
You use a meter to check the voltage on the PWR-ON pin when you push the power switch.
When I test it, it just shows 0.

Are you saying if you keep the meter probe on PWR-ON pin it does not change state when you toggle TV on and OFF? How about DRV-ON, does it also change state when TV is turned on and off? Do you also get the same result doing this same test on the old boards?

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

Quote:
Originally Posted by R_J View Post
The board outputs for a (42") 157.5v/ 341ma I agree he has an open led string.
You use a meter to check the voltage on the PWR-ON pin when you push the power switch.
When I test it, it just shows 0.

Are you saying if you keep the meter probe on PWR-ON pin it does not change state when you toggle TV on and OFF? How about DRV-ON, does it also change state when TV is turned on and off? Do you also get the same result doing this same test on the old boards?

Oh I haven't tried that yet. I just turned the tv on and then put the probe on the power on, I haven't tried DRV-ON yet, what does it mean?

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

You said in an earlier post that the led voltage was 200V. The photo you posted shows that a 42 inch set has a led voltage of 157.5V.
It looks as though you have an open circuit led(s) which is why the set appears not to be powering up. The over voltage protection is probably kicking in and powering down the power supply.

I wasn't exactly sure how much, it wasn't 200v tho, I didn't meant to exaggerate but now that I'm thinking about it, I think it was around 120-150v or something, but if so how could I fix the issue, cuz I replaced the main board and the power supply board.

[budm]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

If PWR-ON is 0V then the rest of the power supplies and the PFC will not be turned on, so without PFC the then the backlight boost converter for the LED drive circuit will not be working either. You better make sure you are testing the Voltage correctly.

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

If PWR-ON is 0V then the rest of the power supplies and the PFC will not be turned on, so without PFC the then the backlight boost converter for the LED drive circuit will not be working either. You better make sure you are testing the Voltage correctly.

so what voltages am I expected to get?

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

You said in an earlier post that the led voltage was 200V. The photo you posted shows that a 42 inch set has a led voltage of 157.5V.
It looks as though you have an open circuit led(s) which is why the set appears not to be powering up. The over voltage protection is probably kicking in and powering down the power supply.

how can I fix that?

[budm]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

so what voltages am I expected to get?

It should toggle between <1 (TV OFF), and >2v (TV ON).

[dick_barton]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

how can I fix that?

Carry out the checks as asked for by the other forum helpers. This helps to provide a better diagnosis of the fault and less guess work on our part. Remeber we don't have the set in front of us.

[nomoresonys]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

carry out the checks as asked for by the other forum helpers. This helps to provide a better diagnosis of the fault and less guess work on our part. Remeber we don't have the set in front of us.

+1000

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

I just checked the LEDS, and I was getting around 157v, and then I checked the power on and off, and it was at 0v.

[dick_barton]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

Measure the dc voltages at all the pins of P201 when in standby and when you attempt to bring it out of standby.

Pin  Name    Standby  Out of standby
1   Power On  xx       xx
2   DRV_On   yy       yy
.
.
.
.
19   GND     zz       zz

Do you have 24V across C203

[nomoresonys]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

Seems like a mainboard or cable from power to mainboard issue with those key voltages missing, you can't just match mainboards by the tv model. Check that the alphanumeric digits on the white stickers of both mainboards match and don't be afraid to do the tests like Dick said.

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

Seems like a mainboard or cable from power to mainboard issue with those key voltages missing, you can't just match mainboards by the tv model. Check that the alphanumeric digits on the white stickers of both mainboards match and don't be afraid to do the tests like Dick said.

Yeah must be the cable, because I already replaced the mainboard and power supply board, but I still dont understand why I was only getting the standby voltage.

[nomoresonys]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

Easy enough to check continuity from end to end on each terminal of connector, so DID the alphanumeric string on white stickers match on both mainboards??

[nomoresonys]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

need to do tests and answer questions as they come or everything just gets all mixed up, did you check the solder joints of the connector??

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

need to do tests and answer questions as they come or everything just gets all mixed up, did you check the solder joints of the connector??

Yes, I checked it all, the numbers and made sure the boards were all right, the only thing I was was that one of the pins were bent a little, where you insert the cable from the power supply board to the main board, but that was an easy fix, I just unbent the pin and it was all good.

[nomoresonys]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

Can try a force on of powerboard, follow closely, unhook cable from powerboard to mainboard at powerboard side, jumper about a 1k resistor from PWR_ON pin to 3.5 standby pin now use another 1k resistor from standby to DRV_ON and another resistor from standby to PDIM, plug power cord into powerboard, now do you have those missing 12 and 24 or whatever was missing and do backlights come on and stay on??

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

Can try a force on of powerboard, follow closely, unhook cable from powerboard to mainboard at powerboard side, jumper about a 1k resistor from PWR_ON pin to 3.5 standby pin now use another 1k resistor from standby to DRV_ON and another resistor from standby to PDIM, plug power cord into powerboard, now do you have those missing 12 and 24 or whatever was missing and do backlights come on and stay on??

I dont have any resistors on hand. I tested the bottom Front LED thats supposed to show the red light. There seemed to be no problem, but the LEDs dont work, the red one at the bottom near the stand. I tested all the cables and nothing seemed to be wrong with them. Im not sure what else to test, my next idea is that maybe theres something wrong with the control buttons on the tv, becuase I don't have the remote. I havent tested the LED backlights yet.

[budm]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

You still did not perform the test as requested in post #21, #31. You are not doing what we are requesting to help troubleshooting the problem. We are up to 39 posts now and still no result for us to see.

[NickIsFluffy]

Re: LG 42ln5300-UB won't turn on and only has standby voltage

You still did not perform the test as requested in post #21, #31. You are not doing what we are requesting to help troubleshooting the problem. We are up to 39 posts now and still no result for us to see.

I dont understand what p201 and the other thing is on post #31