Another LG, 55ln5100 power issues

[Redrebel10]

I used this site a couple years ago and got great help, fixed 3 tvs. One of which I am having problems with again, first time it was a bad mother board. The tv stays outside under a covered porch with a cover on it when not in use. The tv started powering itself off after 2 or 3 seconds following initial start up. At first I could unplug it and after plugging it back in it would come on and stay on. Now it turn itself off no matter what. I can disconnect the tcon and after unplugging and plugging it back in all the backlights will stay on. However, if I just power on and off it will not come back on the led power light will just flash a couple times. In this state the pins on the psb show no readings. Then if I unplug AC and plug back in all the readings go to normal. At first I thought it was the tcon since lights stayed on after disconnecting, but now I realize the psb loses power on the secondary side if I just turn it off and on using the remote or the power button, thanks in advance and hope to get this back running in time for my super bowl party.

[neilc6]

Re: Another LG, 55ln5100 power issues

LG LN series have high rates of backlight failure. Is the tv turning off completely or is the tv on but with the backlights shutdown? Without a led tester, you can monitor the voltage going to the strips to see if they peak up and settle.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

I can see if I can figure out how to test the leds. I was thinking something else since the psb connector shows no readings after powering the TV off then back on using the power button but then it has correct readings if I unplug ac and plug it back in

[budm]

Re: Another LG, 55ln5100 power issues

1) We need good clear pictures of the whole backside of the TV showing all the boards.
2) You need to report all the Voltage readings of the power supply connectors that go to the main board when TV is OFF and when the power switch is activated, you MUST put down the pin name and the Voltage reading for EACH pin so we can easily spot the bad Voltage readings.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

With TV plugged in and without turning on TV the only 2 readings are 3.5v on pdmi2 and pdmi1, no other outputs on the connector. If I power off with button and back on all the readings stay the same. However if I unplug ac and plug it back in all the back lights come on and both 12v pins read 12v, the 24v pin reads 24.3 and both pdmi2 and 1 read 3.5. If I power off using the button it goes back to original state of no voltage readings other than the 2 pdmi pins

[nomoresonys]

Re: Another LG, 55ln5100 power issues

Wonder if it's an eeprom issue, maybe try heating with a hairdryer and or cooling with freezespray or inverted can of duster IC1300, give it about 15 seconds, plug tv in, see if it starts or anything changes.

[budm]

Re: Another LG, 55ln5100 power issues

With TV plugged in and without turning on TV the only 2 readings are 3.5v on pdmi2 and pdmi1, no other outputs on the connector. If I power off with button and back on all the readings stay the same. However if I unplug ac and plug it back in all the back lights come on and both 12v pins read 12v, the 24v pin reads 24.3 and both pdmi2 and 1 read 3.5. If I power off using the button it goes back to original state of no voltage readings other than the 2 pdmi pins

How about the PWR-ON (PS-ON) and DRV-ON (BL-ON)?
You will get the switched 12V/24V when PWR-ON control signal from main board is present.
You will get backlights when PWR-ON, DRV-ON, and PDIMs from main board are present.
So it looks like the main board not always sending out all the control signals.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

I can get all normal readings when I unplug the TV and plug it back in but after that start up if I power off with the button I lose power other than the pdmi pins

[Redrebel10]

Re: Another LG, 55ln5100 power issues

I will be home tonight and can test the pwr-drv pin

[Redrebel10]

Re: Another LG, 55ln5100 power issues

How about the PWR-ON (PS-ON) and DRV-ON (BL-ON)?
You will get the switched 12V/24V when PWR-ON control signal from main board is present.
You will get backlights when PWR-ON, DRV-ON, and PDIMs from main board are present.
So it looks like the main board not always sending out all the control signals.

Ok plugged tv in both pdmi pins have 3.5 and no other readings. Press the power button and no backlights come on but I have 3.3 on the DRV-on pin. and still 3.5 on both pdmi pins. I unplug with tv on and plug it back in and the backlights come on 3.3 dvr, 3.5pdmi and 24.2v and both 12v all have those readings. If I do this with the tcon board connected the backlights only come a few sec. If I disconnect the tcon the backlights will stay on, backlight will only come on by unplugging ac chord and plugging it back in while the tv is on.

[budm]

Re: Another LG, 55ln5100 power issues

"Press the power button and no backlights come on but I have 3.3 on the DRV-on pin. and still 3.5 on both pdmi pins." So what is the PWR-ON (PS-ON) in that condition? I do not see any report on the PWR-OM pin, no PWR-ON = no 12V/24V.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

I was testing the back of the plug assuming they were ps-on and dvr were connected. I'll attach a picture. Weird thing just happened, standby light was on, I pushed power button and no voltage readings other than pdmi, standby light went off and now standby light won't come back on and unplugging ac doesn't help, backlights will not come back on nor will the standby light. I still get 3.5 on pdmi but no other readings

[budm]

Re: Another LG, 55ln5100 power issues

I was testing the back of the plug assuming they were ps-on and dvr were connected. I'll attach a picture. Weird thing just happened, standby light was on, I pushed power button and no voltage readings other than pdmi, standby light went off and now standby light won't come back on and unplugging ac doesn't help, backlights will not come back on nor will the standby light. I still get 3.5 on pdmi but no other readings

The connector pins are labeled so no need to assume anything.
So main board is not sending ALL the needed control signals for the TV to work at this point.
Control signal: <1V = OFF, >2 ~ 3V = ON.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

OK I ordered eeprom ic1300 gonna try replacing that. It was just strange that all the sudden I lost standby light. Thanks for all the help

[vinceroger69]

Re: Another LG, 55ln5100 power issues

Not your tv model number but maybe worth a watch
https://www.youtube.com/watch?v=kbjNq1AyF00&t=362s

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Not your tv model number but maybe worth a watch
https://www.youtube.com/watch?v=kbjNq1AyF00&t=362s

Thanks I'll try that

[Redrebel10]

Re: Another LG, 55ln5100 power issues

"Press the power button and no backlights come on but I have 3.3 on the DRV-on pin. and still 3.5 on both pdmi pins." So what is the PWR-ON (PS-ON) in that condition? I do not see any report on the PWR-OM pin, no PWR-ON = no 12V/24V.

Currently I can not get standby light back on. After removing the connector from psb and testing top and bottom pins I have no voltage on pdmi, pwr or drv. Nor 120v or 24v, only 2 readings are the 2 3.5v pins

[nomoresonys]

Re: Another LG, 55ln5100 power issues

Check D201 and the rest of the diodes, check for bad/cold solder joints on bottom side of board, look closely at the solder joints of components on heatsinks and on transformers, sometimes they look good but are bad or loose.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Check D201 and the rest of the diodes, check for bad/cold solder joints on bottom side of board, look closely at the solder joints of components on heatsinks and on transformers, sometimes they look good but are bad or loose.

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?

[nomoresonys]

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