LG 42LD550 Won't turn on

[korff98]

I have an LG 42LD550 with a problem. The TV was working fine one night until the X-mas tree timer that was plugged into the same outlet switched off. Instantly the TV turned off. When I tried to turn it on, the red light blinks a few times then goes dark. There is no glow at all on the tv screen. FYI, the tv is not plugged in the timer, but was plugged into a surge protector that was plugged into the same duplex wall outlet as the timer.

I took the back panel off the tv, but none of the capacitors are bulged at the top. Any suggestions of next steps?

[nomoresonys]

Re: LG 42LD550 Won't turn on

do you have a digital multimeter?, turn tv on n test the connector for expected voltages, they are written there by the connector, report if any are not correct. as always be careful working with power supply, HIGH VOLTAGE, on primary side can be deadly. check with meter in dc voltage mode. http://www.shopjimmy.com/lg-eay60869...upply-unit.htm

[nomoresonys]

Re: LG 42LD550 Won't turn on

also check the two fuses, the label starts with F, F=fuse.

[korff98]

Re: LG 42LD550 Won't turn on

i have a multimeter and will check voltages. do i put the black probe on any pin marked ground?

[drussell]

Re: LG 42LD550 Won't turn on

Any metal part of the chassis will do fine such as a mounting hole or chassis screw hole.

[korff98]

Re: LG 42LD550 Won't turn on

Both fuses have continuity across them,
The three 12V pins show 0V
The three 20V pins show 0V
The four 3.5V pins are all showing 3.4 - 3.5V

[budm]

Re: LG 42LD550 Won't turn on

What do you get on the POWER ON pin when power switch is activated?

[korff98]

Re: LG 42LD550 Won't turn on

I get 0V on the power on pin.
I did unplug the wire harness that goes to the other board in order to take these measurements. Am I doing this correctly?

[MagicSmoke]

Re: LG 42LD550 Won't turn on

Cable from psu to mainboard needs to be connected, your trying to see if mainboard is sending the POWER ON volts back to the psu to turn it on.

[korff98]

Re: LG 42LD550 Won't turn on

ok. do i measure voltage from the backside of psu?
if i unscrew, do,i need to ground psu to the chasis before powering a testing?
there are two other smaller wire harness on the lower left side of the board, do these need to be plugged in as well?

[MagicSmoke]

Re: LG 42LD550 Won't turn on

Don't unscrew psu. The measurement can be back probed at the connector, just make sure your on the right pin. POWER ON.

When power button is pushed you should see volts come up on P ON pin, if it does not then mainboard has a fault.

The other cables are the HIGH VOLTAGE leads to the backlight. Plug these in also.

[budm]

Re: LG 42LD550 Won't turn on

You can use small needle pin to probe into the connector.

[korff98]

Re: LG 42LD550 Won't turn on

the 12v pins are all reading 12.32v
the 3.5 v pins are all reading 3.4v
the 20v pins are all reading 20.6v
the power on pin is reading 3.22v

[MagicSmoke]

Re: LG 42LD550 Won't turn on

All volts look good. Will it stay on or quit when button released? Could you tell if the backlight came on when all the voltages came up?

[nomoresonys]

Re: LG 42LD550 Won't turn on

check your other connectors you mentioned, maybe, with everything plugged in turn it on, shine a flashlite at the screen see if you see a picture.

[budm]

Re: LG 42LD550 Won't turn on

How about the on/off (bl_on) pin, and A-DIM, P-DIM?

[nomoresonys]

Re: LG 42LD550 Won't turn on

did you try a different outlet or surge protector?

[korff98]

Re: LG 42LD550 Won't turn on

other pins....
NC 0.004v
Error 0.76v
p-dim 2.63v
a-dim 2.62v
inv on/off 0.4v

I am plugged directly into a wall socket, no surge protector.
The screen stays dark, i dont see any image with flash light.
i checked all connectors, they are secure

[budm]

Re: LG 42LD550 Won't turn on

"inv on/off 0.4v" the main board is not sending the Backlights on signal to turn on the backlights circuit.
You can try forcing it on using 100~500 Ohms resistor between the ON/OFF pin and the 3.5V pin but you must remove the wire on the ON/OFF pin first so it not back feed the voltage back to the main board.
You must apply this force on AFTER the power switch is activated (by waiting a few seconds).

[korff98]

Re: LG 42LD550 Won't turn on

i dont have a resistor. will get one tomorrow.
if this works, is there a permanent solution?