MacBook 12" A1534 820-0244: No Backlight

[macdude101]

Got a MacBook 12" 2016 here that outputs to the display but has no backlight, can see the screen with a flashlight. Tried with a known good display and no change.

Measured PPVOUT_S0_LCDBKLT as 0.82V, and narrowed down the issue to something around Q8406, PPBUS_SW_LCDBKLT_PWR is 8.7V but output PPBUS_SW_BKL is 0.82V (should be 8.7V).

This looks to be because LCDBKLT_EN_L is high (8.63V) and thus the input isn't being passed through.

On trying to look at LCDBKLT_EN_L I see it comes from U8401, passing through R8402.

Here EDP_BKLT_EN/BKLT_EN_R is high (3.34V) and I2C_BKLT_SCL and I2C_BKLT_SDA are both present at ~4.6V.

I'm at a bit of a loss as to why LCDBKLT_EN_L is high given this though. Any thoughts/suggestions would be much appreciated.

Schematics/board view can be found here on the forum.

[macdude101]

Re: MacBook 12" A1534 820-0244: No Backlight

I think I may have identified the issue. The D8401/D7701 diode has a forward bias voltage drop of 0.205V matching a known good board of 0.210V however the reverse bias is 0.742V when it should be high/OL which suggests to me this is a shorted diode? U8401/U7701 is then refusing to boost as a result of seeing this on BKL_FB?

Does that seem like a plausible failure mode here before I get to replacing that diode?