Lg 55ga6400 trying to power on but turn off completely

[Jp06]

Hello everyone i have a lg tv model 55ga6400 with an odd issue. It has a standby light but then i press the power button the standby light glow for about 3seconds and shut off completely. It seems like the tv is trying to turn on but won't. There is a thread with similar issues already posted here
https://www.badcaps.net/forum/showthread.php?t=51507
but i can't figure out exactly what which diode and capacitor that he pointed out so i just bought another power supply board (PSB). I'm still experiencing that same problem. Please help! Here are the pictures.
Both the fuses on the PSB are good. Can someone please tell me what is that small board on the left side of the PSB is?
Thank you sooo much!!!

[budm]

Re: Lg 55ga6400 trying to power on but turn off completely

LG EAY62851201 (EAX64908101, LGP4755-13P) Power Supply Unit
http://www.shopjimmy.com/lg-eay62851...upply-unit.htm
Your board is not the same as the one in another thread, your board does not have D607 in the PFC Voltage booster circuit.
Right now you need to measure the DCV between the two legs of the main filter cap C610 to see if the PFC Voltage is present or not and also the DCV of each pin of the connector P201.
You MUST PROVIDE THE PIN NAME, PIN NUMBER AND FOLLOW WITH THE dcv READING FOR EACH PIN.
Pictures provided by shopjimmy.

[Jp06]

Re: Lg 55ga6400 trying to power on but turn off completely

Thanks Budm you actually helped me with 3 tvs so far.
so here are the readings. I also did the readings for p202 and got nothing.

[budm]

Re: Lg 55ga6400 trying to power on but turn off completely

https://www.badcaps.net/forum/attach...1&d=1477625629

OK, pin 1 (pwr-on) of connector P201 is not getting the command on signal from the main board to tell the rest of the power supplies (the switched 12V, switched 24V) board to come on, also not turning on the PFC Voltage booster either.
So that 0VDC reading on pin 1, is that after the power switch is activated?
BTW, the PFC diodes in your board are D601~603.
The small board on the right of the PSB is the LED backlghts driver board.

[Jp06]

Re: Lg 55ga6400 trying to power on but turn off completely

it's zero before i press the power button and 3.3v after.

[budm]

Re: Lg 55ga6400 trying to power on but turn off completely

it's zero before i press the power button and 3.3v after.

OK, that is important info. So when that 3.3v PWR-ON is present you should see the DCV on the legs of the main filter cap jumps up to close to 380~400VDC, if not, you need to check those 3 PFC diodes to see if any one of them show LOW RESISTANCE or not.

[Jp06]

Re: Lg 55ga6400 trying to power on but turn off completely

so after i power on here are the readings...

[zxzANUBISzxz]

Re: Lg 55ga6400 trying to power on but turn off completely

I have the same issue as you have described here. Did you receive a final response from budm? If so what was the ultimate solution?

thanks!

[budm]

Re: Lg 55ga6400 trying to power on but turn off completely

I guess I miss this thread, so OP has the PFC Boosted Voltage, so more in depth troubleshooting to find out why the rest of the power supply does not come on.
There is a fuse sitting right next to that main filter cap, so check that out.

[zxzANUBISzxz]

Re: Lg 55ga6400 trying to power on but turn off completely

this fuse?

[nomoresonys]

Re: Lg 55ga6400 trying to power on but turn off completely

No, it's F101 but always check all the fuses.

[budm]

Re: Lg 55ga6400 trying to power on but turn off completely

I have the same issue as you have described here. Did you receive a final response from budm? If so what was the ultimate solution?

thanks!

BTW, you did not provide us what DC Voltage you have when measure right between the two legs of the main filter cap in the hot side circuit and also the Voltage on all the pin of the power supply connector that goes to the main board. You do have all the needed tools to do repair down to component level including SMD type component, correct?

[zxzANUBISzxz]

When I flash a light on the screen I can see the picture displayed. Does this mean the back light is out and how would I fix this?

[nomoresonys]

Re: Lg 55ga6400 trying to power on but turn off completely

Bud gave a test procedure, did you do it?

[nomoresonys]

Re: Lg 55ga6400 trying to power on but turn off completely

Bud gave a test procedure, did you do it?

Was in post #6, need to do these simple tests to narrow down the problem, be careful it is in the HOT/DEADLY SIDE.

[John_Clark]

Re: Lg 55ga6400 trying to power on but turn off completely

Hi,
I'm working on an LG 50LA6970 with this same power supply board. I get the LG logo light on the bottom of the screen bezel for about 2 seconds and then that goes out and it's black. I've tried the flashlight test and I'm getting no display that I can see.

At P201 the PWR-ON goes to 3.5V when TV is powered on. All the GND, 3.5V, 12V, and 24V pins check out but I have the following voltages at P201: P-DIM=17mV, A-DIM=0mV and DRV-ON showing 88mV. I don't know what these are supposed to be. I don't see any significant ripple on any of the 3.5, 12, or 24V supplies and don't see any obvious blown caps.

P202 all checks out but, again, with the exception of P-DIM and A-DIM and DRV-ON same as the above. When turned on, I have 397.9V on the main filter cap C610 as specified above.

Can anyone shed any light on the A-DIM, P-DIM, an DRV-ON pins? Are these maybe the display inverter power supply pins? I do have the equipment and know-how to fix this but need to know if what I'm seeing on these pins is OK so I can either move on or find the issue with this PS board.

Thanks,
John

[budm]

Re: Lg 55ga6400 trying to power on but turn off completely

1) It is best to start a new thread since yiur TV is not the same model as the OP.
2) Make sure to provide good clear pictures of the whole backside of the TV showing all the boards.
3) P-DIM=17mV = bad. It is PWM type dimming control signal from the main board.
4) A-DIM=0mV It is analog backlights dimming type from main board. The TV may use P-DIM or A-DIM based on requirement. More likely to be using PWM.
5) DRV-ON showing 88mV = Bad. This is the same as BL-ON (Backlights on) signal from main board. <1Vdc = OFF, >2Vdc or so = ON.
6) have 397.9V on the main filter cap C610. This means that the main board is sending good PS-ON signal to turn on the PFC Voltage booster circuit and the rest of the switched power supplies.
So we need good clear pictures so we can provide the test points to test.
What is the history of the TV?

[John_Clark]

Re: Lg 55ga6400 trying to power on but turn off completely

I will get some photos up shortly. The main PS board is the exact same one in the photos above. That's why I posted in this thread. I guess it probably would have been better to start a new thread anyway.

I have a couple of scopes at my disposal--some old Tektronix CRT scopes (a 314 and 475) so I can look at a PWM signal if I need to. Is that signal supposed to come from the main PS board?

The history is a friend brought it over and said it doesn't work. I figured I'd open it up to just find some bad caps but after checking them all (in circuit) with an ESR tester I didn't find any bad ones. I realize I may need to pull them out of circuit but would like to have a direction first as they all visually appear to be OK. Missing a PWM signal sounds like it may be more serious than just a bad cap or two.

[John_Clark]

Re: Lg 55ga6400 trying to power on but turn off completely

Here are some photos of the TV and the boards.

Thanks!

[budm]

Re: Lg 55ga6400 trying to power on but turn off completely

Right now the main is not sending the required signals (BL-ON and Dim) for the backlights to come on.