820-00138 Random black screen

[tlough75]

On the bench I have an 820-00138 that has a strange issue. The backlight flickers and turns off, or stays on. BKLT_EN_R is 3.3V and BKLT_EN_L is 11V when computer is turned off but when I turn the machine on BKLT_EN_L goes to 7-8V and stays, even if I close the screen down. Does this mean U7701 is toast. The backlight will randomly go out, then come back on, then stay off. Can't say I have ran into this issue much.

 

[2informaticos]

"BKLT_EN_L goes to 7-8V and stays"
If you mean LCD_BKLT_EN_L, perfect.

I recommend to test first with known good compatible LCD assembly.
The image still present when backlight goes off?

 

[tlough75]

yeah for the most part. It did glitch out once. By that I mean the Apple logo would come up then the screen would blink, then the Apple logo would come back. It did that about 5 times before I tried to shut it down with the power button, which is not working either.

 

[2informaticos]

Board goes off, or you can only detect backlight issue?
USB activity still present at that time?

 

[tlough75]

I get USB activity because I am booted from external drive. After the initial crash I have not been able to get it to do crash again, just the backlight issue remains. Going to see if I have a test LCD.