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MAcbook Air A1466 - 820-00165 Backlight Issue.

A

arshees

Member
Hi,
Need help with a board random backlight issue. First time i started it worked fine. Restart and no backlight. Now it's no backlight always. Checked the following and noticed 2.8v missing at PWM Pin voltage at the 2 Pin of the resistor R7704.
Measured the VIN voltage through capacitor C7710 - 5V.
Measured the VDDIO voltage through capacitor C7711 - 3.3V
Measured the EN Pin voltage at the 2 Pin of the resistor R7731 - 2.8V.
Measured the PWM Pin voltage at the 2 Pin of the resistor R7704 - Missing
Measured the SCLK voltage at the 2 Pin of the resistor R7753 - 3.3V
Measured the SDA voltage at the 2 Pin of the resistor R7757 - 3.3V..
Replaced U7701 - No change..

What next?
 
A

arshees

Member
Another thing i noticed... With a flashlight at the back i can see the machine boot but it is extremely slow and keyboard and trackpad both not working. Power on off button is unresponsive and even with a battery connected it boots up without pressing the power key. Am i looking at SMC issue..
 
2informaticos

2informaticos

Administrator
Staff member
Did you check SMC_LID signal?
Tried another LIO board/flex and trackpad?
Checked XW7720 integrity?

You didn't mention in any moment the voltage at pin 1 of R7704.
 
A

arshees

Member
SMC_LID measured on R5171 Pin 1 - 0.65 mv. Missing...Changed the LIO board and flex cable. Swapped the board on a working machine and same issue. XW7720 check is pending as i will need to remove U7701. R7704 Pin 1 and 2 both show 0v. In the meantime, if this helps...
 
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2informaticos

2informaticos

Administrator
Staff member
No need to remove U7701, unless you already detect corrosion underneath.
Scratch the smll area near A5 ball.

Do you have now 3V at SMC_LID?
 
Last edited:
A

arshees

Member
Removed U7701 and XW7720 is fine. D7701 pin 2 to U7701 A5 link is perfect. Anything else needs to be checked while U7701 is removed? Ordered a new LP8550 and should take a couple of days.
 
2informaticos

2informaticos

Administrator
Staff member
Replace R5171.
Check J9500 for corrosion on corresponding pin.
Still no backlight if LIO flex is disconnected?
At least SMC_LID must go high.
 
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