820-3476 Intermittent Display

[rany]

This is a rush job, I have no time to investigate properly, and hoping for clues.
We always have display on external monitor, sometimes we have on the internal display, sometimes not. We booted three times, only last time did we get display from internal monitor.
Customer said most times pulling the external monitor leads to having display on the internal monitor.
Internal screen tested with another board, worked every time. Could be a coincidence?
Board does not show any trace of previous repair and no corrosion anywhere.
Screen connector looks good, board connector looks good. Poking at the screen cable does not cause display to come and go.
Hall effect resistor (0 Ohm) is ok. Hall effect component is present and measuring across same as a donor board.
I have continuity from resistor to SMC 100K resistor.
Any clues on where to start are highly appreciated. TIA.

 

[dukefawks]

Only times I had these issue it turned out to be the LCD. Replacing the cable first of course before blaming the actual panel.

 

[rany]

Trying to secure a screen since incoming screen is held at customs.
Tried two new cables in the meantime, twice each, everytime we get no backlight.
Tried the old one back, 4 times, three of which we get no backlight, and once no display.
Will start troubleshooting backlight while waiting for a miracle screen to show up at my door.

 

[rany]

I measured voltages at the connector. Got 12.6V that turn to 39V whenever the display decides to light up.
It did it once when I was testing the voltages, and the LCD cable partially slipped out. I pushed it back in and got backlight.
I will give it back and wait to receive the new screen :-/
P.S.: using new LCD cables. Both give the same result. The original cable is bad, show no display nor backlight.