QN55Q80 backlight good no picture

[jason123]

Hi all,
got this TV for a friend to look at. Non-responsive to PWR button. Main board gets warm, the the optical audio light is on. Faul pin is zero volts. I am getting 33v on Vdrive. 12.76V on B13 & A13. Vamp is 17.3V.

Disconnecting panel cable to main - no change. Disconnecting small ribbon from main to led driver board, backlight comes on.

Do do you guys think? I am thinking main board issue?

[lotas]

All manipulations with disconnecting cables from the panel, you must first install a feedback jumper and disconnect the U-shaped cable connecting the two halves of the panel and then check the behavior of the TV.

[jason123]

All manipulations with disconnecting cables from the panel, you must first install a feedback jumper and disconnect the U-shaped cable connecting the two halves of the panel and then check the behavior of the TV.

Thank you.. Jumper installed (what doe it do?) and the U cable disconnected on one side. Behavior is unchanged. Do I need to try anything in particular?

[lotas]

The feedback jumper simulates that the panel is connected to the motherboard, and runs all the voltages coming from the T-CON, try disconnecting only the Lvds cable, from the motherboard side.

[jason123]

The feedback jumper simulates that the panel is connected to the motherboard, and runs all the voltages coming from the T-CON, try disconnecting only the Lvds cable, from the motherboard side.

LVDS from Main Board to Panel disconnected from the main board side - no change (non-responsive, no activity)

[lotas]

Well then there is a high probability that the problem is in the motherboard...

[Diah]

LVDS from Main Board to Panel disconnected from the main board side - no change (non-responsive, no activity)

LOL. of course will be no Picture as you have only one LVDS. so panel will be out from circuit..
you said you have optic are on.. do you have sound ? did yours LED BL turning on ?

[jason123]

LVDS from Main Board to Panel disconnected from the main board side - no change (non-responsive, no activity)

Main boards are fairly expensive for this TV, so as a last shot I reflowed the processor professionally, and long behold.. TV is alive again! I noticed the processor didn't have any thermal pads on the bottom part of the board, though the metal backing has a raised areas. So I added a thermal pad - Fingers crossed - let's see how long this will last. The fact that a reflow fixes the issue for a bit, means that most main board sold online (by TV repair shops) are reflown and as bad / good as mine
Thanks for the help.

[lotas]

Main boards are fairly expensive for this TV, so as a last shot I reflowed the processor professionally, and long behold.. TV is alive again! I noticed the processor didn't have any thermal pads on the bottom part of the board, though the metal backing has a raised areas. So I added a thermal pad - Fingers crossed - let's see how long this will last. The fact that a reflow fixes the issue for a bit, means that most main board sold online (by TV repair shops) are reflown and as bad / good as mine
Thanks for the help.

There is a professional reball, and there is a reflow, if it is done professionally, it should work for a long time.
The main thing here is that the panel is alive, the rest can be found (motherboard, power supply, ...).