LG 55LH40-UA Wont stay on

[sdubb]

I registered a long time ago, finally got time to post some info on a TV I a having problems with. The TV is an LG 55LH40-UA that when turned on will show a picture for like 2 seconds then cut out then shows again for a couple of seconds, then same things, til eventually it turns off. The LED light on the front of the TV will change from blue to red (red when its off). Opened it up and no bad caps, plus the previous owner replaced the power board thinking that would solve the issue but the same issues are there. I am not sure where to go from here, as most all other TV's I have fixed have been bad caps and they are back up and going. I have tried to find information using the search of what the issue could be and am coming up empty. I did read about the Y SUSTAIN board but this part is all new to me. Any input greatly appreciated. Thanks.

[newtothis]

Re: LG 55LH40-UA Wont stay on

First thing is to get good clear pictures of all the boards and one of entire layout, Get close up shots of any connectors with voltages etc written next to them

[sdubb]

Re: LG 55LH40-UA Wont stay on

Snapped some quick pictures, fuses all seem good, as far as testing voltage, where to start

[newtothis]

Re: LG 55LH40-UA Wont stay on

Ok regarding Y-SUS, This is an LCD not plasma.

Ok while set is running can you take reading using VDC at connector P201. List like this

12v 12.1v
Ps_on = 3v
Stby = 5v

etc etc

Your labels will vary

[sdubb]

Re: LG 55LH40-UA Wont stay on

Yes LCD, read some more after I posted

I had to leave so I will get some voltage readings tonight

On my way out I snapped a picture of the inverter, which is the only thing visually that stands out. It looks like some cold solder joints.

[newtothis]

Re: LG 55LH40-UA Wont stay on

Reflow them anyway

[sdubb]

Re: LG 55LH40-UA Wont stay on

I tried to take some voltages, makes it difficult when it it keeps shutting off
pwr_on 5.09
All voltages are within range to what the board shows

[newtothis]

Re: LG 55LH40-UA Wont stay on

Please list as asked above. Get reading when working and not working please

[sdubb]

Re: LG 55LH40-UA Wont stay on

NC=0.0V
A-DIM=1.65-3.3V
NC=0.0V
24V=24.0V
GND=0.0V
12V=12.1V
GND=0.0V
5.2V=5.2V
5.2V=5.2V
GND=0.0V
GND=0.0V
NC=0.0V

P-DIM=3.3v
ERR=1.4v
INV-ON=4.7V
24V=24.1V
GND=0.0V
12V=11.9V
GND=0.0V
5.2V=5.2V
5.2V=5.2V
GND=0.0V
GND=0.0V
PWR_ON=5.1V

The hardest one was the A-DIM the voltage was all over the place with it TV turning off and on (showing screen and blanking screen out)

Hopefully this helps.

[newtothis]

Re: LG 55LH40-UA Wont stay on

Ok PSU checks out, Most likely main fault then.

Get a ~500ohm resistor and jump a 5.2v pin to PWR_ON pin on PSU with mainboard disconnected from PSU.

Does the PSU shut down now?

[sdubb]

Re: LG 55LH40-UA Wont stay on

PSU won't turn on at all when I jump those pins with the resistor. I am to use the 5.2V and not the 12 or 24V?

[sdubb]

Re: LG 55LH40-UA Wont stay on

So frustrating, ready to toss this TV. It's such a great picture for those 2 seconds it shows an image.

[newtothis]

Re: LG 55LH40-UA Wont stay on

What ohm resistor?

You may need to also jump the other 5.2v to the INV-ON

[budm]

Re: LG 55LH40-UA Wont stay on

NC=0.0V
A-DIM=1.65-3.3V
NC=0.0V
24V=24.0V
GND=0.0V
12V=12.1V
GND=0.0V
5.2V=5.2V
5.2V=5.2V
GND=0.0V
GND=0.0V
NC=0.0V

P-DIM=3.3v
ERR=1.4v
INV-ON=4.7V
24V=24.1V
GND=0.0V
12V=11.9V
GND=0.0V
5.2V=5.2V
5.2V=5.2V
GND=0.0V
GND=0.0V
PWR_ON=5.1V

The hardest one was the A-DIM the voltage was all over the place with it TV turning off and on (showing screen and blanking screen out)

Hopefully this helps.

So are these the readings AFTER the screen goes dark?

[sdubb]

Re: LG 55LH40-UA Wont stay on

I was using a 470 ohm resistor. When I jumped the pins the power button light wouldn't come on. I will try to jump inv.
The voltage I measured were when the screen was lit up.

[newtothis]

Re: LG 55LH40-UA Wont stay on

I was using a 470 ohm resistor. When I jumped the pins the power button light wouldn't come on. I will try to jump inv.
The voltage I measured were when the screen was lit up.

So those are not the reading when it goes off?

[sdubb]

Re: LG 55LH40-UA Wont stay on

No those are the readings when it's lit up. There was a time a few months ago I tried to see if it was working and it actually stayed on for like 30 second. But now it's just back to off/on/off/on to complety off. It just keeps doing that cycle.

[newtothis]

Re: LG 55LH40-UA Wont stay on

Can you get us the readings when its shut itself down?

[budm]

Re: LG 55LH40-UA Wont stay on

I was using a 470 ohm resistor. When I jumped the pins the power button light wouldn't come on. I will try to jump inv.
The voltage I measured were when the screen was lit up.

When you force on the power supply, you MUST disconnect the cable going back to the main board first, which mean you will NOT see any LED on the front of the TV.
The main thing we want to see when ALL the boards are connected is what Voltages are on the pin when the screen goes black.

[sdubb]

Re: LG 55LH40-UA Wont stay on

When it shuts itself off these are the readings

0.0 NC
0.62 ADIM
0.0 NC
0.01 24V
0.0 GND
0.0 12V
0.0 GND
5.24 5.2V
5.24 5.2V
0.0 GND
0.0 GND
0.0 NC

0.01 PDIM
0.01 ERR
0.01 INVON
0.01 24V
0.0 GND
0.0 12V
0.0 GND
5.24 5.2V
5.24 5.2V
0.0 GND
0.0 GND
0.07 PWRON