LG 26LE 5300 Motherboard

[Chaks]

Hi all,
Power surge hit my LG Led TV 26LE5300 and since then the TV switches on , displays the Logo and switches off.

The power adapter ( output 24 volt 2.5 AMPS) is reading 23.5 volts at output.

Opened the TV, checked the Main Board/motherboard (it's single board TV) for any visible blown components but none was found.

Removed the PCB and check the underside of the PCB but found none of the components visibly damaged/blown.

But on the chassis facing the PCB there was a Burn Mark of about 10mm please see attached images.

The mystery is how come the burn mark on the chassis below the PCB while there are no visible blown components on the PCB. Or is it possible that a component has totally blown and disappeared? Should I check anything else?

https://drive.google.com/open?id=1Pc...UXVvwq58E1uTkg

[Andrew F. Ali]

Re: LG 26LE 5300 Motherboard

Sounds like a corrupt software issue. Could you post the picture/s as I am unable to connect to the link you gave. Thanks.

[Chaks]

Re: LG 26LE 5300 Motherboard

Here are the links for the individual images.

https://drive.google.com/file/d/1R5V...0beAUvuQD/view
https://drive.google.com/file/d/1-Xk...SNU2WevlC/view
https://drive.google.com/file/d/1qj8...uS9vA_Jbs/view
https://drive.google.com/file/d/1qQR...yGs4JBMjO/view

Thanks in advance for your time.

[Chaks]

Re: LG 26LE 5300 Motherboard

Posting the images here itself

[Andrew F. Ali]

Re: LG 26LE 5300 Motherboard

I just can't figure out where that arc spot came from, but the board looks physically OK. I'll stick to a corrupt software issue.

[Chaks]

Re: LG 26LE 5300 Motherboard

With reference to PCB schematic the only area of suspect is L7914, Q7501, Is it possible that L7914 blew off without trace. Anyone having the same PCB/motherboard can confirm that L7914 should have been on the PCB.?. Q7501 looks like affected by burn. Other than these components I have not found anything else suspicious in the burnt area.

[budm]

Re: LG 26LE 5300 Motherboard

https://www.badcaps.net/forum/attach...0&d=1528479637
That blank spot is L7914, the inductor L7913 is present which is on the left of L7914. The schematic shows only one of the two inductors will be installed depend on the version of the TV, L7913 is the bigger inductor than the L7914, you have the TV using AC adapter so L7913 is installed for TV using AC adapter as noted in the schematic.
Check the resistance between GND and each end of the L7913, GND against the suspect blown components.

[Chaks]

Re: LG 26LE 5300 Motherboard

I will measure the resistance of the two transistors Q7501 and Q7500 also.
I am unable to identify what component/s blew off. Power fluctuation/surge should have definitely blown some components. The burnt mark on the chassis is still a mystery. Is there a wild possibility that an insect might have got stuck between the chassis and PCB and got electrocuted and left the burnt mark otherwise I am clueless.

There are lot of posts on baking the motherboard in the oven at 180-200 deg C for 10-15 mins. Lot of them were successful though temporarily. Any advice on baking the pcb? though the cause of my problem is a power surge/fluctuation.
Baking the PCB ... I am not sure how I can manage it ... i may damage more components in the process then solving the present problem.

[Chaks]

Re: LG 26LE 5300 Motherboard

Here is a service manual for the LG 26LE Led TV

[budm]

Re: LG 26LE 5300 Motherboard

Get Q-TIP and wipe on the parts to see which one will have black residue.

[Chaks]

Re: LG 26LE 5300 Motherboard

I got the readings measured around the suspected components in the burnt area. I took the nearest ground ( the other ground area on the PCB also had similar readings). My measurements may not be accurate (since I measured in the PCB itself) but at-least can be compared with the readings from a working motherboard.
Anything else I should try?

[Chaks]

Re: LG 26LE 5300 Motherboard

Are My mesurement OK?. or did I do it in the wrong way? (the images posted above). If it is necessary I will remove the components and check them separately (the inductor , transistor, capacitor around the burnt area. Any thing else I should do?.
Is it possible to get a 10mm black burnt mark without any components being blown to pieces.? Please Help.