55 lg model 55uf6450 no backlights

[evanroheff21]

Re: 55 lg model 55uf6450 no backlights

So I guess the 'DRV-ON' pin that changes from 0v to only 75mV is the problem. That should be coming back with 3.2 or 3.3v when fired up, right? Does that mean a failed main board?

[evanroheff21]

Re: 55 lg model 55uf6450 no backlights

Is there any further troubleshooting I can do at the main board to see why it's not sending a 3.3v DRV-ON signal back to the power supply? Is it safe to jumper (with a paper clip or length of wire) the 3.3v signal from another pin on the plug to the DRV-ON pin to see if the backlight is working? Is there any sort of hard reset on the board itself I can perform? There are two tactile press and release buttons on the main board itself, what do they do?

[Andrew F. Ali]

Re: 55 lg model 55uf6450 no backlights

Do not attempt to jumper anything just yet. you may difficult to reverse damage to the Main Bd. Post a clear focused pic of the PSU and the PSU connector that goes to the Main Bd. I may be able to help yo self-test the PSU. What voltages are you getting on that connector at ac Plug-in and at Power on attempt?

[evanroheff21]

Re: 55 lg model 55uf6450 no backlights

Here are the pics you requested. I listed the voltages observed in a previous post, but I can measure and post them again if that's helpful. Let me know what I can do to test.

[Nick's Tvs]

Re: 55 lg model 55uf6450 no backlights

You have a failed main board. No picture, no backlight, no audio but the TV set can be turned on and off is something we have seen at our shop several times in the past. Right now there is a cheap main board for sale on eBay if you take a look at the link below.
The colored snow mentioned in a previous post is also common for these main boards.

https://www.ebay.com/sch/i.html?_fro..._odkw=55uf6450

Good luck

[evanroheff21]

Re: 55 lg model 55uf6450 no backlights

Nick,

Thanks for the information. That's what I was afraid of. Is there any point in me trying to oven bake the board to reflow the solder? That method seems somewhat suspect to me, but if it works, it works, I guess. A lot of people report success on their LG repairs doing that.

[eagle00799]

Re: 55 lg model 55uf6450 no backlights

FYI-I am working on this same model with no backlights, can not see any image but I do have sound. https://www.badcaps.net/forum/showthread.php?t=70368
I sent my main board to https://store-zt3br2s.mybigcommerce....3Dorder_status for repair ant they have sent me a message saying they found nothing wrong with the board.

[DIMITRIO]

Re: 55 lg model 55uf6450 no backlights

see the conector from psu to mainboard.near to the conector where is a piece of glue there is a smd coil.see if there is a bad solder.

[evanroheff21]

Re: 55 lg model 55uf6450 no backlights

Just for the sake of anyone down the road, I bought a replacement main board and the TV is working great. Before I decided to buy a replacement, I tried baking the board in the oven to possibly fix any solder joints (375 for 10 mins). This actually brought the other board back to life, but only lasted about 10 minutes and fizzled out again. I tried baking more (400 for 15 mins) and got about 10 more mins out of it. Either way I knew that back lights, psu board, T-con, and cables were all fine so I felt like there was low risk in replacing the main board (since they are expensive). Thanks for the suggestions.