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[SOLVED]820-3662 no backlight

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ytesfay80

ytesfay80

Member
I have this board that was liquid damaged. The customer said they already replaced the keyboard and battery but the backlight doesn't work and an image can be seen with a flashlight. I have removed the logic board and I don't see any areas with visible corrosion but it does look like they may have cleaned it with alcohol and brush.
I don't have another display assembly to check if the display is the issue.

I measured Pins 1 and 30 of the LCD connector and I got 54.6v on LCD Backlight and 5v on Pin 30. With only the screen plugged in I got 3.32v on BKL_EN and 0v on Pin 1 of R7747(SMC_SYS_KBDLED / BKLT_PWM_KEYB).

I'm not familiar with the backlight circuit on these Macbook Pro's so I'm not sure where to measure.
 
M

MDY

New member
54.6v on LCD Backlight means display is not detected. Bad screen, lvds cable or lvds connector. Check them.
 
ytesfay80

ytesfay80

Member
How is that an image appears on the screen if the display is not detected? The cable and connector look perfectly fine upon inspection.
 
ytesfay80

ytesfay80

Member
Okay with no keyboard plugged in there was 0v on BKL_PWM and I was just wondering if that may be an issue before I try replacing the connector and cable.
 
Last edited:
ytesfay80

ytesfay80

Member
I just measured again and there was 0v on both sides of R7747, a probe point for BKL_PWM and Pin 12 of U7701 and there was 0v while backlight output was 54.6v. I even measured Pin 11 of U7701 and it showed 5.95v so the multimeter is working fine.
 
D

dukefawks

Administrator
Look where R7747 and tell me what PWM it is controlling.....Then look at U7750. But again, this is a dead connector/cable/LCD.
 
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