Hi.
Macbook came in originally with no backlight.
Confirmed display worked - with torch from behind could see login screen.
Replaced backlight, which blew again.
Tried with known good display assembly after replacing fuse - unit worked.
Returned to customer.
Now, customer returned it with the same issue.
The fan goes to maximum and stays there after a few seconds.
Replaced backlight fuse - still no backlight.
Tried with another known working display assembly - same.
Checked voltage at PPVOUT_SW_LCDBKLT: ONLY 12.46v
Which makes me suspect U9701.
Checked inputs to U9701:
PP5V_S0_BLK: 5v
PPBUS_SW_BKL:12.6v
PP3V3_S0_BKL_VDDIO:3.3v
LCD_BKLT_PWM:2.63v (measured at pin2-r9704).
This last one is suspicious:
PPBUS_SW_LCDBKLT_PWR:12.6v (measured at pin1-R9731)
BUT pin2-R9731 measures 0.05v!
The resistance across R9731 reads 280K ohm.
However across R9715 showed only around 100 ohm, not the 100K it should.
I desoldered R9715, and measured the two points under it and I get the same 100 ohm.
Pin2 on R9715 shows 100 ohms to ground.
Given there is only 0.05v going to BKL_EN (A3 on U9701) measured from pin2 on either R9731 or R9715, does this mean that U9701 is internally shorted?
By the way, SMC_LID is 3.42v.
I do not have any spare U9701, so I removed one from another unknown faulty same logic board.
Afterwards, all the voltages are the same, and the same symptoms, although I cannot rule out that the board I took it from had the same issue.
Any suggestions on what I may have missed, or what to test next.
Any help greatly appreciated.
Macbook came in originally with no backlight.
Confirmed display worked - with torch from behind could see login screen.
Replaced backlight, which blew again.
Tried with known good display assembly after replacing fuse - unit worked.
Returned to customer.
Now, customer returned it with the same issue.
The fan goes to maximum and stays there after a few seconds.
Replaced backlight fuse - still no backlight.
Tried with another known working display assembly - same.
Checked voltage at PPVOUT_SW_LCDBKLT: ONLY 12.46v
Which makes me suspect U9701.
Checked inputs to U9701:
PP5V_S0_BLK: 5v
PPBUS_SW_BKL:12.6v
PP3V3_S0_BKL_VDDIO:3.3v
LCD_BKLT_PWM:2.63v (measured at pin2-r9704).
This last one is suspicious:
PPBUS_SW_LCDBKLT_PWR:12.6v (measured at pin1-R9731)
BUT pin2-R9731 measures 0.05v!
The resistance across R9731 reads 280K ohm.
However across R9715 showed only around 100 ohm, not the 100K it should.
I desoldered R9715, and measured the two points under it and I get the same 100 ohm.
Pin2 on R9715 shows 100 ohms to ground.
Given there is only 0.05v going to BKL_EN (A3 on U9701) measured from pin2 on either R9731 or R9715, does this mean that U9701 is internally shorted?
By the way, SMC_LID is 3.42v.
I do not have any spare U9701, so I removed one from another unknown faulty same logic board.
Afterwards, all the voltages are the same, and the same symptoms, although I cannot rule out that the board I took it from had the same issue.
Any suggestions on what I may have missed, or what to test next.
Any help greatly appreciated.
