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

[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?

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?

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?

[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

[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

[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

[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...

[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?

[nomoresonys]

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

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

[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

[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.

[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?

[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!

[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

[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

[diif]

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

Stencils are available for the LG chips but the last one I did I used a universal stencil and a bit of kapton tape to mask off the inner part where there are no balls.

[Diah]

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

from reading various threads lg seem to suffer from bad bga soldering could be ram could be main ic

this issue to me look like when you start the car but the starter keep on LOL... he had some kind of script repeat it self to take place.. however he tried to heat. and disconnect MICOM action. but i do suggest to freeze but he went to heat.. because the tv was turning on but not complete no panel vcc and optical ports still until now didn't lit on. i would start freezing instead of heating..

[vinceroger69]

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

This maybe a set that gets put aside for a while in the hope a replacent mainbord becomes available does the likes of shopjimmy etc list a alternative board?
i thinkk this forum has a for sale/wanted section maybe post in that thread too regarding a working mainboard needed.

[Scoff]

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

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

Thankfully I didn't get as far as clicking 'Buy' on the T-Con board

I will resolder the cap which is not straight, as per your post #76, however it does have good electrical contact on both sides.

I will also remove the heatsinks from the DDR and IC chips to expose them all.

It is good that the issue is isolated to the MB at least.

[Scoff]

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

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

Sadly I don't have anything as advanced as a BGA machine, as other than the odd basic soldering job in the past, mainly auto-electrics, I'm very much an amateur/Noob - but very willing to learn and try things.
I think re-balling would be a bit too much to tackle with my lack of experience, and the outlay for the equipment would be too much for a one off job.
I could look at getting a price for sending the board off to get the main ICs and DDR re-balled as see if it is cheaper than a new TV as I have no idea

Wow not seen that Phil guy's channel before - just watched some of the highlights of that epic PD4 APU reballing by hand