LG 49UB850V nothing on screen.

[stav242]

Hi,
I have a LG 49UB850V
Power PCB EAX65613901 (1.6)
Main Board EAX65684604 (1.0)

symptoms are:
Standby light illuminates when power connected but when Power button pressed, Standby goes off but no sound or picture.
Previous owner said it just went off whilst watching it and wouldnt power on again.

Check Backlights (side lit) and all good.
Power board flashes LED LD701 five times in sequence. - searches seem to indicate this is a fault with DRV signal from?

Voltages all look good from PSU, can see 3.5V, 12V and 24V on C28 (from PB > MB).
PWR_ON changes from 0 to 3.5V
PDIM1, PDIM2 and DRV_ON do not change - they stay at 0v.

it would look like a MB fault.

removed wifi module
tried holding SW1901 at power on, and after for long period.
i have tried freeze spray on IC1901 (SPI) - no change
checked pin 8 on IC1901 has stable 3.5v
USB port has stable 5v
no optical port RED light at all at any stage.
checked for shorts on Caps and Coils.

what else can i check on MB ?

[nomoresonys]

Re: LG 49UB850V nothing on screen.

prolly mainboard fault, not sending the backlight on signal.

[nomoresonys]

Re: LG 49UB850V nothing on screen.

see if you can trace the drv_on wire back thru the mainboard.

[nomoresonys]

Re: LG 49UB850V nothing on screen.

maybe try freezing up IC101 and try it, freeze up the heatsink then try it.

[stav242]

Re: LG 49UB850V nothing on screen.

Traced the DRV_ON pin, labelled, following a schematic i found on this forum for the 55UB850V, that pin is labelled INV_CTL, connects to R2309, and then to an IC on the bottom left of the board, IC3000 to pin19.

Looks like IC3000 = R5F100GEAFB in a 48 pin package.

IC seems ok, has 3.5v but doesnt seem to be activating the DRV_ON signal.

I tried freezing IC101 - no change.

got the backlights on jumping the DRV_ON,PWR_ON and 3.5v so seems to indicate Powerboard is working ok.

any other suggestions - or should i start looking for a replacment board.?

[nomoresonys]

Re: LG 49UB850V nothing on screen.

is R2309 reading the proper ohms?

[nomoresonys]

Re: LG 49UB850V nothing on screen.

could try heating IC101 with a hairdryer and try it, heatsink is on there so get it nice and toasty, then try it while its still hot.

[nomoresonys]

Re: LG 49UB850V nothing on screen.

I think I would try a replacement mainboard if you can find one reasonable, unless someone here knows whats wrong with it, can be tough figuring out exactly what but sure seems like a mainboard issue. Some have luck with diy reflows if its a bga issue, lots of reflow videos on youtube, of course some techniques are better than others.

[nomoresonys]

Re: LG 49UB850V nothing on screen.

for replacement mainboard, you need to match up the numbers on the white sticker, usually CAN NOT just go by tv model or the silkscreen writing on the board.

[lotas]

Re: LG 49UB850V nothing on screen.

Traced the DRV_ON pin, labelled, following a schematic i found on this forum for the 55UB850V, that pin is labelled INV_CTL, connects to R2309, and then to an IC on the bottom left of the board, IC3000 to pin19.

Looks like IC3000 = R5F100GEAFB in a 48 pin package.

IC seems ok, has 3.5v but doesnt seem to be activating the DRV_ON signal.

I tried freezing IC101 - no change.

got the backlights on jumping the DRV_ON,PWR_ON and 3.5v so seems to indicate Powerboard is working ok.

any other suggestions - or should i start looking for a replacment board.?

R5F100GEAFB is MICOM, a microcontroller from Renesas has firmware inside, it controls the launch of the TV from standby to operating mode and vice versa.

[stav242]

Re: LG 49UB850V nothing on screen.

yes.

[stav242]

Re: LG 49UB850V nothing on screen.

OK, so ive got it working.

searching through the forums, i saw some other LGs with IC100 reflow fixes... so as ive nothing to loose i thought i would try it.
https://www.badcaps.net/forum/showthread.php?t=100402

so lifted up the white heatsink and loaded it up with flux paste round the IC edges (only 3 of them as i the heatsink/shield was obstructing one side) - then used hotair tool set at 450C and melted the flux for a minute around the edges.

ive only tried it twice and fired up no problem.... will leave till the morning and check it again to ensure its fixed it.

thanks all. will update tomorrow.

[nomoresonys]

Re: LG 49UB850V nothing on screen.

nice work, hopefully it will last.

[lotas]

Re: LG 49UB850V nothing on screen.

No, it will not last long, warming up the chip is just a diagnostic, not a repair.

[nomoresonys]

Re: LG 49UB850V nothing on screen.

he did a little more than warm it up, its a reflow, granted not under ideal conditions but a reflow it is.

[diif]

Re: LG 49UB850V nothing on screen.

It wasn't long enough, by about 3 minutes. Its doubtful much if anything melted.

[nomoresonys]

Re: LG 49UB850V nothing on screen.

so why don't you give him a profile then?

[nomoresonys]

Re: LG 49UB850V nothing on screen.

heres a PROFESSIONAL reflow by Nick: https://www.youtube.com/watch?v=IkFCE42zoLM

[stav242]

Re: LG 49UB850V nothing on screen.

well its still working, its not being sold or fixed for a paying customer, just a cheap TV for a family member so no issue if it fails, i can try a different approach then.