A1708 820-00840 No backlight (SOLVED)


I have an 820-00840 with no backlight. Tried multiple screens but no difference.

Took the board out and it seems that Q8400 is getting its 12.9v PPVIN on pin 4 but the hate voltage is also 12.9v on pin 3 so isn't opening.

I can't seem to figure out why pin 3 isn't dropping. The resistance between pin 4 and 3 is 80k so seems fine there.

Any help would be greatly appreciated


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Any history available?
Do you get image for sure?

DP_INT_HPD goes high?
Check it with LCD connected!

At least check for image on external monitor.


Hi 2informaticos, Thank you for the quick reply. I just sorted it thankfully.

It tested as low ohms on PPVOUT_S0_LCDBKLT so I decided to inject 5v into that line and have a look on FLIR

The issue was with capacitor C8470 shorting.
Replaced and now works fine.

I was having an off day obviously for not just doing this sooner.

Thanks again