Repairing LG49UB850V TV

[Diver300]

There is an LED on the power supply board that flashes 5 times every 10 seconds or so, otherwise no indication of anything.

A new power supply board has been tried but with no change.

Has anyone got any suggestions for any better targeted fault finding? Are there any diagnostic tests that I can do?

 

[Nigel Goodwin]

OK, have you downloaded the service manual?, and have you googled for the fault?.

The manual is available from:

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.

elektrotanya.com

And google provides lot's of hits on it, one to YouTube which shows the main board getting replaced which cures the fault - it's rather vague though, as the audio is in Tagalog

Basically LED flashing is an error indication, but there's no mention of what the number of flashes means in the service manual, perhaps it 'might' be explained on training courses, if LG actually do anything like that.

But even with Sony manuals, where they explain the codes, there's often codes which aren't included (and occur), and the codes often lead you to somewhere totally irrelevant.

What usually happens is, as the TV boot's up, it has to set up numerous IC's via the I2C bus, as it does each one it waits for a reply - if it doesn't get a reply, it stops from going any further, and flashes the LED the requisite number of times. However, if there's a fault on the I2C bus, then it will fail at the first chip on the bus, regardless of where the fault is. Depending on the set, once all the I2C bus devices have passed, it 'may' then check the LCD panel and backlighting, depending on the make and model.

There's a load of fairly crappy fault finding pages at the rear of the manual, you might try those?. I must admit, I was amazed to even find a circuit diagram in the manual, as most don't bother these days as spares are usually only available at panel level - although, as usual, there's no diagram for the PSU, the part you've got the most chance of repairing!.

But going from the Tagalog guy, main board?.

 

[rjenkinsgb]

I can't read the PSU connection label text in the photo, but from my recent LG experience, there are likely two different PSU enable signals on that connector, one for general power and one for the screen power.

On the TV I did, only one half of the PSU was being switched on by the main board.

I heated the main IC area on the control board as much as I dared without parts dropping off & that got it working temporarily, few hours possibly.

Another control board from ebay fixed it.
(That was an LG OLED55B6).

 

[tepalia02]

You can check the PCB to see if there is a broken trace or short circuit.