820-01236 backlight fault

[2informaticos]

Image should come before backlight is enabled.
This rule is mandatory on any computer, to avoid artifacts displayed on the screen.
Backlight must appears only after image is steady.

Looks like LCD is not correctly detected, in your case.
Be sure all traces, small coils and resistors are good, on the video connector area.

Unfortunately, no schematic/boardview available for this board.
Try to compare with schematics from 2015 and older.

 

[Kappy]

It's very strange this one.. I've check all the resistors, coils etc and everything looks normal. The only thing that isn't normal is the diagnostic lights. I've never seen this configuration before.

I will have to wait until I get another in to check.... I'll keep you updated.

 

[Kappy]

Ok so after receiving another imac I've now found the problem to be the screen.. Just goes to show that don't ever trust what other people say.

Also maybe to help others, the diagnostic light work different on this model.

In order of light up
2 - mains plugged in
3 then 5 - power on
1 - GPU
4 - screen