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a1707 820-00281-a no backlight

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Nicus009

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Hi all,
I have a macbook a1707 with a board 820-00281-a. The screen backlight does not work. I first replaced the capacitor after the d8410 diode. The voltage rose to 10-12v. , the backlight does not shine. There is still no voltage on ISIS_LCDBKLT_P, although there is a voltage of about 11 volts on ISIS_LCDBKLT_N.
Can you tell me how to solve this problem with the backlight.
I am attaching a photo with notes on the voltage at the backlight control area.
SKM_C224e23072614440-1.png
 
It's a boost regulator circuit; IF the CPU is enabling the backlight and the controller IC U8400 is OK, you should see a logic-level PWM drive signal on pin 4 of that, feeding through to the gate of Q8401

If there is no drive signal, either the IC is dead, not being commanded on from the CPU, or is sensing a fault, eg. such as excess current (from the voltage across R8400).
 
Have you tried all the keyboard reset sequences for PRAM etc? some corruption in the settings can lock out the backlight control.

 
Have you tried all the keyboard reset sequences for PRAM etc? some corruption in the settings can lock out the backlight control.

No,if i remember i just try only one combination on keyboard,i'll try this
If it helps,i'll reply
Thanks
 
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