LG OLED55A1PUA

[repair-it]

I have a 2 year old LG OLED OLED55a1pua TV that turns on (power light comes on), relay clicks but picture not present. Are there any known faults with this TV? I've read elsewhere on the inet that others have had the same issue but no remedies that I could locate. One person said they bought a replacement board kit from shop jimmy and it didn't help. (Their stuff is usually reliable however they do not test, visual inspection only...sooo ... could still be a bad board) Visual inspection showed nothing unusual, fuses are good. Voltage checks pending.

[Diah]

if the relay clicks only one time ( turn ON ) and there no other second click (Turn OFF ) are good sign to repair it.
this is happened for following reason
1- Micom on MB didn't send signal order for T-CON 12V or OLED VCC ( this also happened if the firmware clutching , send INSTOP " hard reset" by service remote could solve it ) sign of this issue the Optic audio output lit red... but there are no 12V on T-CON driver boards .... or No OLED VCC >21V
2- NO OLED VCC issue at Micom or at PSU didn't switch the circuit on ( need to test the PSU as stand alone ) i did explain many time at OLED Topics
3- OLED VCC socket burn or lost contact... need to inspect the downside of the sockets from both side
at the end Photos of the whole boards and V measurements will help allot.

[repair-it]

When I press power button, I hear a click, voltage goes to 20v then drops to 17v. The 12v does the same (goes to 12v) and drops to 7v after attempt to power up. I believe there is a faulty component issue on the power supply board but have yet to start testing. Pics attached.

[Diah]

When I press power button, I hear a click, voltage goes to 20v then drops to 17v. The 12v does the same (goes to 12v) and drops to 7v after attempt to power up. I believe there is a faulty component issue on the power supply board but have yet to start testing. Pics attached.

this is information useless as you didn't mentioned where did you make the measurement.. i think your Power boards are fine. so don't miss with it .. to explain more in detail... see the Photo
1- T-CON 12V , 2, OLED Cell VCC >21V
disconnect the socket No 2 from PSU side.. and turn on... measure the voltage on the socket pins and the other socket NO 1.

[repair-it]

Voltages were taken from the connector on PS that goes to main board. The PS shuts down almost immediately after attempt to power on TV. I neglected to state that initially there was no voltage present on the T-CON or OLED connectors. I did check the T-CON board for shorted caps, none found. After removing #2 as you suggested, no voltage on that socket when attempting to power up and a momentary 6v on the T-CON connector when attempting power on.

[Davi.p]

Hi, are you able to test the tcon at bench with a fixed PC PSU ? You can connect the + to the fuse near the connector for the main board, then gou can use also + input direct from PS board..

[Diah]

Voltages were taken from the connector on PS that goes to main board. The PS shuts down almost immediately after attempt to power on TV. I neglected to state that initially there was no voltage present on the T-CON or OLED connectors. I did check the T-CON board for shorted caps, none found. After removing #2 as you suggested, no voltage on that socket when attempting to power up and a momentary 6v on the T-CON connector when attempting power on.

this is new satiation you are describing right now... i will go there are error at yours measurements... cause T-CON 12V how it come only 5V.
also to narrow the fault
1- disconnect all sockets from PSU.. and test the PSU alone .. you have the print chart of the main socket on boards
A- if yours STB 6.7V or above... mean it will go up to 12 after PSU turn on... for this type you need to use Step down circuit to have 3.3V to make the test..
B_ if STB 3.3V then you can go straight to test it.... STB to power on .. STB to VCC_ON --STB to T-CON ON.... and so when you jumper them you should have all V on main socket--- and socket 1 and 2

if yours PSU stand alone test was successful .... keep yours jumpers in place and leave the MB disconnected from PSU and its LVDS disconnected from T-CON ... just put in place socket 1 and 2 in place and power on... if T-CON and OLED module are fine yours Panel will power on and displaying colors.

[repair-it]

Hi, are you able to test the tcon at bench with a fixed PC PSU ? You can connect the + to the fuse near the connector for the main board, then gou can use also + input direct from PS board..

I have tried powering the T-CON with PS and monitored under thermal camera on my bench. All ok.

[repair-it]

I'm sorry I don't understand where I should apply the 3.3v.

[Diah]

I'm sorry I don't understand where I should apply the 3.3v.

i think yours STB are more than 3,3 X. so all sockets disconnected from PSU , just plug it in wall and messure which point you have V. i think the yellow marked and it will be 6-8 V... so you need to have stepdown circuit to bring it always down to 3.3V and connected all together the three Red marked.... then you can check on the pins of all sockets if there correct V. speci ally the sockets 1 % 2

[repair-it]

ok, I will try. FWIW all 20v pins currently measure 13.7v. The 12v pins all measure 7.8v. Knowing that, is it still safe to proceed with what you had suggested with the 3.3v? Just want to be sure before I do it. Does this mean that the 3.3v is missing & the cause? BTW, Thank you very much for the help.

[Davi.p]

20VS stands for 20volt Sound.. 12VM is 12volt Main and is the standby rail + normal state main circuits rail, the lower state measurement is probably the low load standby state, so put some 1A -2A load at least on 12VM and observe the voltages increase.. your tcon test is reported totally wrong, am i the only one able to do some tests without an expensive thermal cam? ;-(

[Diah]

The 12v pins all measure 7.8v. !!! 12VM you mean with blue color ? for us doesn't matter now since we will use ( should / must ) Step down circuit to have 3.3V to feed all together the three marked with red color.... its better to use the low one line

[Diah]

ok, Does this mean that the 3.3v is missing & the cause? BTW, Thank you very much for the help.

NO.. you have 7.8V this is STB.... the main boards will step it down to 3,3V and send it back to PSU... now yours PSU look fine..... this low 7.8 will ho high to >12V when PSU turn on... this why never do any things if you don't have step down circuit to have 3,3V to play game like MB to let PSU work and later T-CON and panel too with out MB help

[repair-it]

Sorry, yes '12VM' (voltage on both 12VM's was 7.8v). I will attempt this over the weekend, I have to remove board to test further on my bench. If the Power supply board does start up properly after applying the 3.3v, wouldn't that mean the 3.3v is missing and it is a power supply board issue?

[Diah]

Sorry, yes '12VM' (voltage on both 12VM's was 7.8v). I will attempt this over the weekend, I have to remove board to test further on my bench. If the Power supply board does start up properly after applying the 3.3v, wouldn't that mean the 3.3v is missing and it is a power supply board issue?

NO again.... you heard the relay click once.. this mean 100% the main boards send first 3.3V to power up..... 3,3 volts generated by down step at MB..
to narrow the fault we took out MB from the system. and test PSU first if its OK... then we test it again with T.CON and panel.. with out NB .. if all fine we do know where we need to look close after HW

[Davi.p]

Sorry a mistake.. put a 5v zener diode on the GND hole (anode) and Power on (cathode), then a 10k resistor from power on to 12Vm.. then test outputs..
otherwise you put 10k from power on to Gnd and 27k from 12vm to power on..

[Diah]

never use any zener or other to have 3,3V... this is very wrong... if you don't have external 3,3V Step Down circuit or 3,3V Regulator,, you can use the Main Boards circuit by connect only one cable from 7.8V to MB sockets... search after 3,3V on MB.. usually the Step down circuit will be close to the socket on MB... after u found this rail solder wire on the point and at the other end of the wire use 1K R connect to the three market point early... 1K R we use here to protect the MB in case you did wrong or used other pins on PSU.

[nomoresonys]

Thanks Diah for keeping things straight and correct.

[repair-it]

ok, to clear up any misunderstanding this is where I am at right now, I did not remove power supply board but decided to give this a go one more time. I plugged the main board back into the power supply board and now all voltages ARE present 🙄as listed, including T-CON & OLED on power supply board. I have NOT reconnected the T-CON or the OLED yet.

If there is an issue with either one (will do one at a time) What should be monitored when doing this? I would presume the corresponding connector for supply voltage of each on the power supply board?🤔 If one or the other is 'bad' what should happen to indicate that?


Update - I left power on & just went back to check voltages on the OLED & T-CON connectors 10 mins later and both are now at 0V. Does this TV go into a sleep mode automatically?