LG 42lb5820 Won't Turn On with 3 Blinking Red Light

[Wildwind]

Hi all,

My 2 year old 42" LG 42lb5820 won't turn on with 3 blinking red light. I measured the voltages output on the power supply board and they were correct with 3.5V (standby), 12 V and 24V output. The LED blinked 3 times with the LG logo sometimes flashed on and then off to black screen.

It has the EAX65610206 motherboard so I will be looking for a replacement board.

Sorry for the NOOB questions below:

Do I need to get the exact board that came out of a 42" TV or anything in this LB58B series will do (ie 32", 40", 50", 60")? Do they have specific firmware for that TV size or they are all the same?

Also, I live in Australia, can I get a board from the US with the same part number or the TV tuner is different on the board (ie NTSC instead of PAL)?


Thanks.

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Also, there was no voltage output to the LED driver boards thus no LED backlight

[dick_barton]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Have you looked carefully with a bright light to see if there is any sign of a picture eg. menu on the screen?

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

I used a torch and could not see any picture or menu. The TV still responded to the remote for turning on and off

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Also, there was no voltage output to the LED driver boards thus no LED backlight

Update: there was ~90VDC across the +ve and -ve terminal of the LED backlight connector but there was no light.


I know the LED brightness is PWM controlled. Could someone confirm that I can drive or test the LED backlight directly using a variable DC power supply?

Thanks.

[dick_barton]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Does your power supply board give the Led voltage written on it?

Do you have photo's of you power supply, top & bottom?

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

The PSU had labelled voltages for other rails (which were all OK) but not the LED's voltage. I measured +90V on +ve and 12V on -ve (just two active pins on the white connector at the top so the LED driver is built into the PSU PCB. And I'm trying to turn it on manually just to make sure that the LEDs are still OK.

The PSU is a fairly common EAX65423701 LG power board but I don't think the PSU is faulty but the LED strips and/or the mainboard are faulty.

It' still turns on and off so the mainboard is responsive and not completely dead.

[budm]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

You need to find out if your are getting the BL-ON DCV command signal to turn on the LED driver circuit or not, the 98VDC reading is indicating that the boost converter circuit is not running.
Per chart on the board, it shows LED supply is 208V/ 235mA.
What you need to do is to leave Black probe on the chassis, red probe on the LED+ then turn on the TV and see if the dcv GOES UP HIGHER than 98VDC for seconds or not (when BL-ON is present) and then drops down to 98VDC.
LG EAY63071901 (EAX65423701)
http://www.shopjimmy.com/lg-eay63071...pply-unit.htm#

Pictures provided by shopjimmy.

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Thanks for your reply Jimmy,

It goes above 98V for a fraction of a second not enough to register 200V on my slow DMM.
The PWR_ON went HIGH (3.5V) when turned on but the DRV_ON never went HIGH.
Is the DRV_ON an input or output from the PSU board? Should it go HIGH as well?

[dick_barton]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

The board appears to indicate that the led voltage is 208V. The DRV_On should be high and is an output from the mainboard to the power supply.

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

The board appears to indicate that the led voltage is 208V. The DRV_On should be high and is an output from the mainboard to the power supply.

I did try the PS board (without the m/b connected) with the PWR_ON and DRV_ON pins tied to High (3.5V) but the screen did not light up. P_DIM was 3.5V. The 208 VDC was there on the +ve pin and then dropped back to 98V but the screen did not light up. So the LED backlight must be faulty then!

[dick_barton]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

This may help you.
https://www.youtube.com/watch?v=2pyuXwNkBMA

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

This may help you.
https://www.youtube.com/watch?v=2pyuXwNkBMA

The DRV-ON never went high so the voltage was constant at 98V (with or without load) as the inverter circuit was never activated. I was trying to see if the LED would light up OK.

[budm]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

I did try the PS board (without the m/b connected) with the PWR_ON and DRV_ON pins tied to High (3.5V) but the screen did not light up. P_DIM was 3.5V. The 208 VDC was there on the +ve pin and then dropped back to 98V but the screen did not light up. So the LED backlight must be faulty then!

Sounds like open circuit in the LED string some where.

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Sounds like open circuit in the LED string some where.

That was what I was afraid of (dismantling the LED assembly ).

BTW, I did a voltage measurement between the +ve and -ve terminals of the LED connector and it never went very high as though both pins went high together. Should I tie the -ve pin to ground (without the m/b connected test) to make sure there is a high-ish potential difference between them.


Sorry for all the noobie questions as I am curious on the new LED LCD TV technology. I have substantial knowledge in electronics but not on LED LCD TV

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Sounds like open circuit in the LED string some where.

Do you know if the the DRV-ON pin would go high if there is an open circuit in the LED string?

Is the P-DIM input or output from the mainboard?

I have opened up the display and found quite a few (11) dead LEDs and I will replace them individually using a SMD/heatgun workstation

Also, if the main CPU is dead would the TV still respond to the remote control?

Thanks.

[budm]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

If there is a pull-resistor for the Base of the switched transistor then the DCV on the DRV pin will be solid high around 2.5~ or more, if there is not pull-up then the DCV will be floating around.
P-Dim (PWM Dimming) is from the main board.
See example of SAMSUNG. BLU-ON (PDF page 2, 7) is the same as BL-ON , DRV-ON.

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Thanks for the info Budm

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

Do you know if the the DRV-ON pin would go high if there is an open circuit in the LED string?

Is the P-DIM input or output from the mainboard?

I have opened up the display and found quite a few (11) dead LEDs and I will replace them individually using a SMD/heatgun workstation

Also, if the main CPU is dead would the TV still respond to the remote control?

Thanks.

UPDATE: I got some replacement SMD LEDs and managed to replace all the dead ones. The LED backlight still would not come on (DRV_ON = low) so the mainboard is faulty as well. It came on when I manually pulled it HIGH so the PS board is OK. Already tried to re-flow the main IC but it did not help

I have the wait for a PAL mainboard to come on eBay

[Wildwind]

Re: LG 42lb5820 Won't Turn On with 3 Blinking Red Light

UPDATE: I managed to buy a second hand mainboard (from a 50LB5820) and it worked OK. However, there was a bit of non-uniformity as the new LEDs were a bit brighter than the old LEDs and they came through to the picture.

And I was wondering if I the installed the diffuser and the thin reflective film inside the panel wrongly. I did not think it was the case if there were back to front/up side down etc. then the clip/screw holes would not line up as they should act as aligning holes.

Does anyone know if this is the case? It works OK at the moment but the non-uniformity is a bit distracting