LG55UB850V no picture or audio - flashing LED's help please?

[vinceroger69]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Yes there has to have been an issue with these boards, as even though the model is a few years old, I would have though there would be a few boards kicking around in working condition. Perhaps most people that have had issues in the past have binned the faulty board and replaced rather than fixing the faulty component on the board. Understandable given the time it takes to diagnose - especially when you have no experience!

I would love to be able to fix the MB if at all possible, for my own satisfaction, but I understand that perhaps there is only so far one can go, even with all the help from the experts on this forum!

from reading various threads lg seem to suffer from bad bga soldering could be ram could be main ic so remove re ball the ics would be ideal if had correct stencils and bga machine but ics could be faulty internally too.
not sure if you watch phils youtube channel but he re balls bga by hand
https://www.youtube.com/watch?v=XiER-Zxo-54&t=27386s

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Does this test show the the T-Con is actually OK, or could it still be faulty? What about the Optical audio port?

as expected.. T-CON full function.
the Optical ports working direct with Main CPU IC100 on LG and some other brands too. so the issue 100% MB. ignore the order of t.con if you can.

the MB we will not able to track and test unless you naked the DDRs and main IC from the heat sinks .
BTW you need back to solder my request at post #76

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

i still think this is a mainboard fault though and must be common issue as non available online.

Yes there has to have been an issue with these boards, as even though the model is a few years old, I would have though there would be a few boards kicking around in working condition. Perhaps most people that have had issues in the past have binned the faulty board and replaced rather than fixing the faulty component on the board. Understandable given the time it takes to diagnose - especially when you have no experience!

I would love to be able to fix the MB if at all possible, for my own satisfaction, but I understand that perhaps there is only so far one can go, even with all the help from the experts on this forum!

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

So jumper removed and transistor soldered back onto the MB, so MB is complete again.
Fitted it back to the TV, removed the LVDS cable from the T-Con, connected a jumper wire from the 12v J71 to T-Con Fuse F1.
Powered the TV on and backlights came on, no buzzing from T-Con cap like this, and voltage stable at 11.8v at fuse F1.
So T-Con cap only buzzing when it is getting it's 12v feed from the MB via the LVDS.
Does this test show the the T-Con is actually OK, or could it still be faulty? What about the Optical audio port?

[vinceroger69]

Re: LG55UB850V no picture or audio - flashing LED's help please?

i still think this is a mainboard fault though and must be common issue as non available online.

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

yes, use the PCB 12V rail to F1. LVDS must be disconnected and CN5 Vsyn should be in place on t_CON

[nomoresonys]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Sure use the adjustable, just don't take it past 12 volts.

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

well i dont think the t-con defect.. but it could be one of VDD line on mainboards which are make the conflict on T-CON. if you feed the T-CON with 12V VCC with out LVDS i dont think this caps will buzzer at all and the VCC will remain stable

I have an adjustable DC power supply which goes up to 30v, should I use this or should I take 12v from the power board to the T-Con, bypassing the LVDS, to check for buzzing / fluctuation?

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Thank you both for the links! The ebay T-Con is the nearest match I have seen, although the title doesn't specify 55UB850V - but it looks like it should be correct.

One other thing which I don't think can be T-Con related is the Optical audio port not lighting up red. While I wait for the T-Con to arrive, is there anything I can check/test to see what's wrong there? Again, way back at the start of the troubleshooting this was lighting up red...

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

well i dont think the t-con defect.. but it could be one of VDD line on mainboards which are make the conflict on T-CON. if you feed the T-CON with 12V VCC with out LVDS i dont think this caps will buzzer at all and the VCC will remain stable

[vinceroger69]

Re: LG55UB850V no picture or audio - flashing LED's help please?

This should be the correct one
https://www.ebay.co.uk/itm/125119290...wAAOSwj~th9-5b
see link about lg tcon
https://www.tvparts.co.uk/lcd-tv-spa...-LG-TCON-BOARD

[nomoresonys]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Good one there to help you with testing: https://www.youtube.com/watch?v=DiW6nNk1TYA

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

OK i've checked as you said, and there are several pins from the LVDS that have a direct connection to the negative side of the cap on the T-Con board, however there are none that I can find that have a direct connection to the positive side of the cap.

It's certainly very strange how the T-Con may have become faulty, as it was seemingly working fine back at the start of the troubles, after first unplugging the WiFi module.

When looking for a replacement board, I can easily match the details:

Model: V14 TM120 UHD Ver0.6
P/N: 6870C-0502C

as this board seems to be used across a variety of LG models/sizes.

The numbers I cannot match are those printed on the white sticker -

NBD25G
3703M1

Are these simply to uniquely identify my particular board, like a serial number, or do I need to keep looking to find a board with these same numbers in the white sticker?

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Thank you. I soldered a short jumper wire between those 2 points.
I turned the tv on and the screen came on, however, the same voltage fluctuation and buzzing came back from the T-Con cap

can you disconnect the LVDS from T-CON side.. and check the cap you mentioned if it had direct connection at any of LVDS socket pins on t_CON
if there are no direct connection to the sockets pins ...

then remove the jumper.. solder back Q2301 at it place.
go to the cheap option replace T-CON.. but the questions i cant find answer why T-CON got damaged, or its really damaged.

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Thank you. I soldered a short jumper wire between those 2 points.
I turned the tv on and the screen came on, however, the same voltage fluctuation and buzzing came back from the T-Con cap

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Back to 0.835v at fuse F1 which seems to be a 'normal' reading when no panel_VCC 12v is present - which is what I was seeing back in post #39 when the screen was not turning on.

okay... now we are going to see the buzzer caused by micom panel_CTL or the T-con the caps you before talked about, or we do have other issue we can narrow it by this work.

we are going to bypass panel_CTL by keeping Q2301 out side the boards and put jumper (see photo just connect the 2 points with soldering wire between them ) this is by pass Q2302 to feed panel_vcc to the T_CON.

TV should turn on normal with screen complete with hope no buzzer.

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

LOL you're right - it was very surgical looking! My first time soldering any components this small so I thought better safe than sorry, especially with all the surrounding components that are ever smaller!



So after cleaning up I left the transistor on the side and fitted the MB back to the TV.

System went into standby and then powered on via RC like you said. Backlights came on, and the following stable voltages:

23.98v
11.89v
3.533v

Back to 0.835v at fuse F1 which seems to be a 'normal' reading when no panel_VCC 12v is present - which is what I was seeing back in post #39 when the screen was not turning on.

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

So does this indicate a problem/failure between Collector and Emitter?

wow it look hospital Operation room. did you put on white shirt LOL !!

as i expected yours Transistor at best condition , so keep it on side right now

i would like, you turn on the tv ( just be sure the place of the Transistor clean / no shorts at the pins )

at this point we will not have any panel_VCC 12V. but the tv should power on with RC... check the 12,V & 24V and 3.5 rails if they are in range and stable .

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Thanks very much for the explanation of the transistor Q2301.
I masked the area on the MB surrounding Q2301, and found a smaller soldering Iron tip so instead of hot air I used the soldering iron tip plus flux and some de-solder wick. I was able to keep the heat isolated and away from the nearby tiny resistors and caps.

I successfully removed Q2301 from the board The brown marks on the tape are just solder flux and not burn marks!





I measured Q2301 in diode mode while off the circuit board and here are the results:

- probe Base, + probe Collector = 0L
+ probe Base, - probe Collector = 0.716

- probe Base, + probe Emitter = 0L
+ probe Base, - probe Emitter = 0.703

- probe Collector, + probe Emitter = 0L
+ probe Collector, - probe Emitter = 0L

So does this indicate a problem/failure between Collector and Emitter?

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Thanks for the link. There are a few similar transistors, however I do not know which values are ok to be different to the values of the 2sc3052?

maybe you are excited about yours measurements of Q2301 and yours compare with Q2303 specially both the Emitter goes to GND. this reading could confused you.. the only correct matter when this Q2301 to take it out of the boards then you can continue the excitement. WHY :

Q2301 Base receive Panel_CTL from IC 3000 ( MICOM ) Pins 4. .Micom the one turnoff the set if there are error.. and it send not ONLY CTL to Panel but also the WIFI power_ON too ( we are back to first time when you get run the set only when you disconnected the WIFI Module ) also now you have just TIMING CLK each 2 seconds the buzzer and dropping Panel_VCC which this ( MICOM ) the one send switching Panel_VCC 12V. via the Panel_CTL.

this short explanation i hope to give you the courage to mask all components round Q2301 and take it in one piece to measure it out circuit.