LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

**nomoresonys** · 09-18-2023, 03:48 PM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Well then that looks like your problem, mainboard not sending drv_on signal, so no backlights.

**Diah** · 09-18-2023, 03:51 PM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

put yours DM on T_CON Fuse 12V with Ref to TV chassis , then turn on did you have any reading?

**nomoresonys** · 09-18-2023, 03:51 PM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Anyone with a good memory remember? maybe it needs a good diy reflow of the bga.

**nomoresonys** · 09-18-2023, 03:53 PM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Do you have picture with the flashlight test?

**Diah** · 09-18-2023, 03:59 PM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by nomoresonys

Do you have picture with the flashlight test?

friend,,, his psu error led lit red blinking.... mean there are issue on one rail,
the rails are... 12v mb 24v mb 12v t-con and bl led

**Diah** · 09-18-2023, 04:23 PM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

my last post over here.... as i wrote in my post #7 yours issue 99% BL.... forcing BL as stand alone never mean they are fine... you have edge LED BL, and each LED unit hat build in ziner Diode which can easily by time get open or shorted,,, yours TV from 2014.... LED life time almost 10,000 hours

**nomoresonys** · 09-18-2023, 04:31 PM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

That was my first thought too Diah, It's 49 inches, I would have already had it tore down and be inspecting the leds quite closely.

**Seb932** · 09-19-2023, 04:20 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by Diah

my last post over here.... as i wrote in my post #7 yours issue 99% BL.... forcing BL as stand alone never mean they are fine... you have edge LED BL, and each LED unit hat build in ziner Diode which can easily by time get open or shorted,,, yours TV from 2014.... LED life time almost 10,000 hours

Update on next round: First I've disconnected the T-Con from MB. Then hooked up 12V to T-CON F1 and also forced DRV_ON and POWER_ON.
BL lights up and Panels cycles White/Red/Green...nothing, i would expect blue. Only a break (for blue) then starting from the beginning.

To rule out BL finally i also stripped the TV down afterwards, edgelight is working pretty well. No dark LEDs, burned spots or anything like that. Put everything together again...

My conclusion => T-CON has at least a problem (Blue color is missing)

Attached Files

**Diah** · 09-19-2023, 04:43 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

pull out only the wire of DRV-ON from the PSU socket, and jumper the pins of the socket with 3.5V .. all other LVDS / ribbon cable should be in place... then turn on what you will have on the screen

**Seb932** · 09-19-2023, 04:58 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by Diah

pull out only the wire of DRV-ON from the PSU socket, and jumper the pins of the socket with 3.5V .. all other LVDS / ribbon cable should be in place... then turn on what you will have on the screen

Nothing because T-CON doesn't receive PANEL_VCC from MB. Thats why i've hooked up it directly to see if panel and T-CON are ok...
PANEL_VCC will be enabled by Q2303 with PANEL_CTL signal from IC3000, but signal is not coming (as well as DRV_ON from IC3000)...

I expect IC3000 is "waiting" for some other signals until releasing DRV_ON and PANEL_CTL....maybe related to the missing lower voltages on MB...

**Diah** · 09-19-2023, 05:06 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

i see... t-con 12v come via lvds.. . then its MB... try warming it at the area close to LVDS socket... and check any change

**Seb932** · 09-19-2023, 05:27 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by Diah

i see... t-con 12v come via lvds.. . then its MB... try warming it at the area close to LVDS socket... and check any change

Tried it, warmed up MB with a heatgun. Switched on, no change at all.

**Diah** · 09-19-2023, 06:17 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by Seb932

Tried it, warmed up MB with a heatgun. Switched on, no change at all.

IC3000 on LG are MICOM, had his own script and controlled too with main firmware start script. you should have micro switch to reset it... it could help..
other wise repairing MB not easy task even for LG service center

follow the service manual ab page 31 and feed it with low V and to check low V are working fine

**Seb932** · 09-19-2023, 06:45 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by Diah

follow the service manual ab page 31 and feed it with low V and to check low V are working fine

Have already tested the micro switch beside IC3000. It's the same like power on the TV. It triggers the MICOM reset => Power_On sequence starts again and stuck with the same result.

Originally posted by Diah

follow the service manual ab page 31 and feed it with low V and to check low V are working fine

First question: You think about feeding additional external low voltage into the mainboard to bypass the voltage regulators?

Second question: what about the missing blue color in panel test mode? Could it be also a panel problem? How to test? If panel is dead I would not spend additional time...

**nomoresonys** · 09-19-2023, 06:59 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Ok, I'm going back to my original diagnoses, reflow the bga.

**Diah** · 09-19-2023, 07:00 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by Seb932

Have already tested the micro switch beside IC3000. It's the same like power on the TV. It triggers the MICOM reset => Power_On sequence starts again and stuck with the same result.

First question: You think about feeding additional external low voltage into the mainboard to bypass the voltage regulators?

Second question: what about the missing blue color in panel test mode? Could it be also a panel problem? How to test? If panel is dead I would not spend additional time...

1- take out the MB and simulated the lowV start from STB 3.5 and down to all emmc V and so on

2- the blue you have... other wise you will never see white RGB when all high level same value will present white color.

**Seb932** · 09-19-2023, 07:09 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by Diah

2- the blue you have... other wise you will never see white RGB when all high level same value will present white color.

Damn, you are right

Originally posted by Diah

1- take out the MB and simulated the lowV start from STB 3.5 and down to all emmc V and so on

lowV start signal is available on all the regulators, as well as VDD 12V. I've checked this already. Means input is ok for all voltages, but output not for low voltage.
Looks like something grounds/overlay the output-signal...
Output IC3000 => Voltage Regulation IC => Result
POWER_ON/OFF1 => IC2304 5V => +5V_NORMAL OK
POWER_ON/OFF2_1 => IC2301 3.3V => +3.3V_NORMAL OK
POWER_ON/OFF2_2 => IC2302 2.5V => +2.5V_Normal OK
POWER_ON/OFF2_3 => IC2303 1.5V => NOK PWM/rectangle signal with ~650kHz and 12V Peak
POWER_ON/OFF2_3 => IC2300 1.0V => NOK PWM/rectangle signal with ~340kHz and 12V Peak
POWER_ON/OFF2_4 => IC3409 1.2V => NOK PWM/rectangle signal with ~500kHz and 12V Peak

Attached a picture from the scope with one of the regulator outpts...

Attached Files

**Diah** · 09-19-2023, 07:24 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Originally posted by Seb932

Damn, you are right

lowV start signal is available on all the regulators, as well as VDD 12V. I've checked this already. Means input is ok for all voltages, but output not for low voltage.
Looks like something grounds/overlay the output-signal...
Output IC3000 => Voltage Regulation IC => Result
POWER_ON/OFF1 => IC2304 5V => +5V_NORMAL OK
POWER_ON/OFF2_1 => IC2301 3.3V => +3.3V_NORMAL OK
POWER_ON/OFF2_2 => IC2302 2.5V => +2.5V_Normal OK
POWER_ON/OFF2_3 => IC2303 1.5V => NOK PWM/rectangle signal with ~650kHz and 12V Peak
POWER_ON/OFF2_3 => IC2300 1.0V => NOK PWM/rectangle signal with ~340kHz and 12V Peak
POWER_ON/OFF2_4 => IC3409 1.2V => NOK PWM/rectangle signal with ~500kHz and 12V Peak

Attached a picture from the scope with one of the regulator outpts...

we do know the input are fine.. you did run PSU standalone...
IC3000 from its behavior are fine for me.. we need to consider on emmc V and IC1000 V.
you can start to capture the start log via JTAG..

**Seb932** · 09-19-2023, 07:54 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Tried to find L2302 to check eMMC V. During search I found L2322 is burned (resistance 440Ohms), which is output for 1.2V

Is it ok to bride the coil for testing purposes or better replace with some other SMD coil?

Attached Files

**nomoresonys** · 09-19-2023, 08:01 AM

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Sure bridge for testing.

LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

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