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LG 3D 4K TV repair - UB980 range 65UB980 79UB980 84UB980

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Interesting to see the XD ICs are available on AliExpress, I hadn't thought to look. I think my main board is probably too far gone though.

I think 3D should be possible using any computer as the input. As far as I can tell it's just simple passive 3D with row interleaved polarisation for L/R. So most good media players should be able to output row interleaved 3d stereo.

The TCON has a 3D_EN_LGD_120Hz pin, otherwise known as PCID enable/disable. Not sure exactly what that pin does, or what PCID stands for. The TV is marketed with 200/240Hz capability - although it has a 120Hz panel. I think maybe it's something to do with how it manages the odd/even gate drivers for the panel (VGH_Odd/VGH_Even) - maybe switching them twice per frame so it can output interleaved 240Hz with a progressive 120Hz input? Since the pin is just a simple high/low input it should be possible to test.

I'd assume the 3D playback is something that should work with a lot of other mainboards, even 60Hz ones, assuming they were from a TV that also had line interleaved polarisation (passive 3d).

Indeed these TVs are row-interleaved passive 3D, so the display can be driven directly with a 4K row-interleaved 3D signal (e.g. from a PC) to achieve 3D display - but... in order to support Blu-ray 3D playback (using HDMI 1.4 frame-packed 3D), a 4K passive 3D compatible motherboard would be required.

I compared the UB980 and the UH950 motherboards I have, and unfortunately the TCON ribbon connector is a different pitch, so unfortunately it's not an easy swap.
BTW: I found the service manual for the 65UH950 here:

Just repaired a 75" LG LED 4k TV (75UK65 model) had backlight and sound but nothing else. It was the second similar LG 4K model I fixed, both had the same fault, so I am guessing it is quite common.

For this particular fault the gate driver high (+16V) or low (-8V) voltage is being pulled down by a shorted smoothing cap.

Easy to check with just a DMM and without getting all technical with scopes or circuit diagrams, firstly pull out one of the two ribbon cables from the TCON board to the TFT to see if half the screen goes white. If it does, then one side is shorting the supply. in both my faults it was just a case of going through the ceramic caps on the long PCB at the bottom of the screen which the faulty ribbon cable came from with a continuity tester to find the shorted one.

Might help someone save a good TV from landfill.


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