LG 70UH6350 (UB.BUSMLJr)

[nonsub]

Hello folks. Pulling my hair out here having received my TV back from a local shop with a diagnoses of failed mainboard and TCON (but irrepairable due no parts availability.) Armed with some basic electronics skills, meter, and youtube this is where I got to:

a) Connecting AC, power/standby LED = ON.

b) Pressing the power button or RC = power/standby LED = off > blinks 3 times > off.

c) No backlight at any point. Could not see any display using flashlight either.

d) Toslink is lit

e) No ethernet signal detected on network switch (who know if enabled by default?)

f) Subsequent presses (or long press) on power button do nothing

g) RC power button (unlike main button) continues to go in and out of standby (by checking power board voltages) and Toslink going on and off.

h) Have swapped out all boards and actually 2 x motherboards but with E-pray parts so who knows but in all cases the results are the same.

i) Measured voltages per attached seem OK? However DRV_ON is missing. From everything I've found so far that means a bad mainboard.

j) Disconnected mainboard from power supply. Put a 11k resistor on PWR_ON and one on DRV_ON. Connected these both to a 3.5v supply. Note that there is every possibility this isn't the right way to do this? Result = all backlight LEDs seem to go on.

k) Have checked the DRV_ON pin from motherboard side to make sure there isn't an open wire.

l) After a bit power supply cycles green LED flashes X 5.


So other than having an original board go bad then 2 X E-pray ones exhibit the same problem (actually I don't recall if I had the original light up Toslink or handle remote, and I can't check because I ruined that board with a heatgun!) could I be missing anything else here?


Thanks for any help!

[nomoresonys]

Re: LG 70UH6350 (UB.BUSMLJr)

did you match up the alphanumeric digits of the white or orange sticker on the replacement mainboard/s with the one on your original mainboard?

[nomoresonys]

Re: LG 70UH6350 (UB.BUSMLJr)

PLEASE NOTE: This board is compatible with TVs with SVC code 70UH6350-UB.BUSMLJR (found on sticker on back of TV).

Part number can be found on the orange barcode sticker on board.

[nonsub]

Re: LG 70UH6350 (UB.BUSMLJr)

did you match up the alphanumeric digits of the white or orange sticker on the replacement mainboard/s with the one on your original mainboard?

Thanks for replying.

Back housing label shows: UB.BUSMLJR

Original board shows no reference to the above.

All 3 show EBT64174324 which I think is the important number?

There are several other sets of numbers that don't match.

[nomoresonys]

Re: LG 70UH6350 (UB.BUSMLJr)

ok, that eliminates the possibility of a mismatch, makes me wonder if it's in the backlight circuit, so none of the mainboards will give you a voltage at the drv-on pin? like when you have your meter lead on it and you power up, theres just nothing?

[Storyteller12]

Re: LG 70UH6350 (UB.BUSMLJr)

Most likely you got a bad mainboard or wrong part. Part # is EBT64174324. Shopjimmy has 1 mainboard in stock but not cheap at $199

I doubt your tcon is bad. I had this tv before and it was just mainboard that needed replaced.

[Diah]

Re: LG 70UH6350 (UB.BUSMLJr)

DIm are high.. DR_ON 0 mean you have LD BL issue ( shorted )
can you show us photos on the whole back. to see how boards connected.

[Storyteller12]

Re: LG 70UH6350 (UB.BUSMLJr)

If I recall correctly this is an edge lit TV and The backlights have a huge heatsink attached to them. I don’t think you can separate the heatsink from the backlights either. I’ve never seen this tv with bad backlights. Only bad mainboard or panel failure

[Diah]

Re: LG 70UH6350 (UB.BUSMLJr)

I’ve never seen this tv with bad backlights. Only bad mainboard or panel failure

why not.. if LED had limited life circle..
from his point b) Pressing the power button or RC = power/standby LED = off > blinks 3 times > off.
it tell MB are fine... micom fine too and can handle error where it exist
with out photos and exact test every things possible

[Storyteller12]

Re: LG 70UH6350 (UB.BUSMLJr)

why not.. if LED had limited life circle..
from his point b) Pressing the power button or RC = power/standby LED = off > blinks 3 times > off.
it tell MB are fine... micom fine too and can handle error where it exist
with out photos and exact test every things possible

You may be right. There is a first time for everything. I'm just saying I've never seen this model with bad backlights.

OP: Post pics of the back and let's troubleshoot some more.

[nonsub]

Re: LG 70UH6350 (UB.BUSMLJr)

You guys are awesome; thanks for the replies! Will follow up when I get home.

[nonsub]

Re: LG 70UH6350 (UB.BUSMLJr)

TV is direct lit w/local dimming.

With the motherboard cable disconnected and 3.5V fed to PWR_ON and DRV_ON it seems all backlight LEDs go on. 100V measured at the LED PS test point. Around 47V on standby. Doesn't this suggest th backlight is fine?


With the motherboard cable connected, after the first exit of standby the TV's power button does nothing but the RC power button I do see the Toslink LED toggle, the standby voltages toggle (but again only 60mV for DRV_ON.) I measure ~72V when out of standby at the LED PS test point, ~47V on standby.

Irrelevant = speakers disconnected since disassembly but pretty sure I would have tested with them connected at some point. Testing done with TCON ribbons both connected and disconnected.

In the image top right of the power board that's just a regulator I used to get 3.5V from 7.8v point to feed DRV_ON, PWR_ON.

[Diah]

Re: LG 70UH6350 (UB.BUSMLJr)

try to open the IR section at middle front of the TV and disconnect only WiFi module & Bluetooth if exist then power on normal.. read the out put voltage at the PCB socket
& if there 12V at the T-CON fuse from both side !

also can you make clear focused photo of the LVDS socket area !?

[nonsub]

Re: LG 70UH6350 (UB.BUSMLJr)

try to open the IR section at middle front of the TV and disconnect only WiFi module & Bluetooth if exist then power on normal.. read the out put voltage at the PCB socket
& if there 12V at the T-CON fuse from both side !

also can you make clear focused photo of the LVDS socket area !?

LVDS socket in this picture I have the ribbons disconnected.

Disconnected module and same behavior.

But before voltage and fuse check... what is the expected behavior if TCON is completely disconnected? Shouldn't DRV_ON go high even if no TCON?


thx

[Diah]

Re: LG 70UH6350 (UB.BUSMLJr)

it make no sense if T-CON disconnect ... micom will not send drv_on and will not deliver 12V to T-CON

[nonsub]

Re: LG 70UH6350 (UB.BUSMLJr)

it make no sense if T-CON disconnect ... micom will not send drv_on and will not deliver 12V to T-CON

Thank you. OK I will check this but this is also the second tcon board.

If blacklists go on when manually 3.5v drv and our on they are for sure good or could still be the problem? I ask because I see another thread on this unit that this board will not boot if backlight problem and to cut safety wire to test (but where us safety wire?)

Thx

[Diah]

Re: LG 70UH6350 (UB.BUSMLJr)

as i said before if t-con disconnect will be no BL... and if the panel some where at corner broken.. BL will be off as no Picture..

put every things original in place... remove the cover of the panel puffer boards... look if you have on left and right side U ribbon cable.. need to disconnect and turn on each time of left and right... if there are no U ribbon.... half screen disconnected from T-CON will be fine... and always think on the t-con 12 V if exist

[nonsub]

Re: LG 70UH6350 (UB.BUSMLJr)

OK thanks so reconnected PSU > MOBO and TSCON LVDS.

I did NOT remove frame to see if any corner LCD damage yet.

Both sides of TCON fuse = ~12V (11.45V)

Did you want me to try completely removing U LEFT (1 and 2) and test then reconnect and remove U RIGHT (1 and 2) or did you mean something else (actually probably you mean disconnect LEFT 2, test then reconnect and try disconnect RIGHT 1 and test?) And when disconnecting what am I looking for to happen? I could randomly test but will wait for your exact instruction.


Thanks!

[Diah]

Re: LG 70UH6350 (UB.BUSMLJr)

each side left or right of the panel buffer boards its enough if you disconnect only one side of the U ribbon

with this test you need to check if ur BL come on or not and if not could be the panel will show 3/4 picture of the screen size... use tourch light and u may hear sound if you feed it with signal.

[nonsub]

Re: LG 70UH6350 (UB.BUSMLJr)

each side left or right of the panel buffer boards its enough if you disconnect only one side of the U ribbon

OK still same behavior