Another LG, 55ln5100 power issues

[budm]

Re: Another LG, 55ln5100 power issues

I inspected everything under the psb and all looked good. What are the 2 3.5volt pins for? meaning are they responsible for sending power to the mainboard and it triggers all the other voltages?

https://www.badcaps.net/forum/attach...2&d=1579659498
The 3.5V pins are the 3.5V standby power supply so the Voltage should always be present.
The exposed pins you see on the top side of the board are for the ODD number pins.
You count the pins correctly?

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Did you check all the diodes on powerboard? just check m in diode mode, should get a reading in one direction usually .2~.7 or so then reverse the test leads and should read OL, simple diode testing there: https://www.youtube.com/watch?v=mMXDa5hVzXA

Thanks I'll try that when I get home

[nomoresonys]

Re: Another LG, 55ln5100 power issues

If any diodes read off, lift a leg out of circuit and test again.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Did you check all the diodes on powerboard? just check m in diode mode, should get a reading in one direction usually .2~.7 or so then reverse the test leads and should read OL, simple diode testing there: https://www.youtube.com/watch?v=mMXDa5hVzXA

https://www.badcaps.net/forum/attach...2&d=1579659498
The 3.5V pins are the 3.5V standby power supply so the Voltage should always be present.
The exposed pins you see on the top side of the board are for the ODD number pins.
You count the pins correctly?

Budm. Since losing the standby light and can no longer get the backlights on, I can only get 2 readings on your psb connector and that is both of the 3.5 pins.(top pins)

[Redrebel10]

Re: Another LG, 55ln5100 power issues

If any diodes read off, lift a leg out of circuit and test again.

I was going to ask if I needed to take it out of circuit diode, D201 reads the exact same if I flip your neg and positive leads

[budm]

Re: Another LG, 55ln5100 power issues

Budm. Since losing the standby light and can no longer get the backlights on, I can only get 2 readings on your psb connector and that is both of the 3.5 pins.(top pins)

That means the 3.5V Standby power supply is OK, the main board uses that 3.5V to run, when power switch is activated then the main board will send all the needed control signals to turn on the rest of the power supply, so at this point you have problem with the main board due to the fact that you do not even get the standby lights to be on when the main board has 3.5V to run.

[budm]

Re: Another LG, 55ln5100 power issues

I was going to ask if I needed to take it out of circuit diode, D201 reads the exact same if I flip your neg and positive leads

D201 is for the 3.5V standby power supply, if it is bad you will not be getting the 3.5V.
What are the EXACT readings showing on your meter?

https://www.shopjimmy.com/lg-eay6281...upply-unit.htm

[nomoresonys]

Re: Another LG, 55ln5100 power issues

I was going to ask if I needed to take it out of circuit diode, D201 reads the exact same if I flip your neg and positive leads

Yep, take it out of circuit, if it reads the same I would replace it.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

D201 is for the 3.5V standby power supply, if it is bad you will not be getting the 3.5V.
What are the EXACT readings showing on your meter?

https://www.shopjimmy.com/lg-eay6281...upply-unit.htm

Like. 27 on that one but if that controls the standby voltage I guess it's good since I can still get 3.5v on those 2 pins. Gonna try heating up the main board and see if that does anything, have the new eeprom coming in Friday, the main board replacement is 60 so hoping I can find a cheaper fix

[budm]

Re: Another LG, 55ln5100 power issues

Like. 27 on that one but if that controls the standby voltage I guess it's good since I can still get 3.5v on those 2 pins. Gonna try heating up the main board and see if that does anything, have the new eeprom coming in Friday, the main board replacement is 60 so hoping I can find a cheaper fix

It is rectifier diode for the 3.5V power supply, if it conducts both direction then the output will not be DC any more.
0.27 Ohms in both directions? Did you test it in Ohm mode? I do not think you have bad diode otherwise there will be no 3.5VDC on the output.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

It is rectifier diode for the 3.5V power supply, if it conducts both direction then the output will not be DC any more.
0.27 Ohms in both directions? Did you test it in Ohm mode? I do not think you have bad diode otherwise there will be no 3.5VDC on the output.

OK thanks, yes I tested in diode mode same mode I would test a fuse for continuity. So at this stage are you thinking the fix would be replacing the main board?

[vinceroger69]

Re: Another LG, 55ln5100 power issues

lg tv mainboards seem too suffer from bga solder issues some people use a proper reball set up some people do a reflow using either a heat gun or a lamp etc various methods on youtube this is one thread on this forum
https://www.badcaps.net/forum/showthread.php?t=55409

[budm]

Re: Another LG, 55ln5100 power issues

OK thanks, yes I tested in diode mode same mode I would test a fuse for continuity. So at this stage are you thinking the fix would be replacing the main board?

Test in diode mode will not show result in Ohm, it will show in Volt. Use Ohm mode to test fuse since bad fuse can have high resistance more than 10 Ohms so it will still show as conducting which will lead you to believe that the fuse is good when using diode mode to test the fuse.
You have main board problem as I indicated before due to the fact that you do not even have LED indicator.

[will62]

Re: Another LG, 55ln5100 power issues

You have main board problem as I indicated before due to the fact that you do not even have LED indicator.

+1

While you're waiting on the eeprom, why don't you run a couple of tests to make sure that the PSB and LEDs are good. See attached diagrams.

Edit: Once you have the resistor jumpers in the connector, put something like cardboard down, so that if you lay the connector down, the resistors do not short on the chassis or main board.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Thank you to all helping, I will update tomorrow after getting new eeprom and I will try all that is suggested

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Well tried the new eeprom (no change) and tried baking the main board for 10 minutes at 385 degrees and still no change. So it looks like I buy a new main board or trash the TV

[nomoresonys]

Re: Another LG, 55ln5100 power issues

Looks like it's getting pretty expensive, I would start keeping it indoors if you get it fixed.

[diif]

Re: Another LG, 55ln5100 power issues

Well tried the new eeprom (no change) and tried baking the main board for 10 minutes at 385 degrees and still no change. So it looks like I buy a new main board or trash the TV

Lead free solder melts around 422F. You weren't hot enough.

[will62]

Re: Another LG, 55ln5100 power issues

Before you toss that main board, do you want to check some of the required voltages?

I'm including the SM for a 47LN54**. The main board in that set is also used in the 55LN5400. I believe the only difference in the "5100" is that it doesn't have the SmartShare option.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Before you toss that main board, do you want to check some of the required voltages?

I'm including the SM for a 47LN54**. The main board in that set is also used in the 55LN5400. I believe the only difference in the "5100" is that it doesn't have the SmartShare option.

Sorry I already ordered a new main board before you posted that