MacBook Pro A1286 Mid 2012 no backlight but display working

[Gigabit2]

I have a MacBook Pro mid 2012 with no backlight but the display is working. Have shined a light through the Apple logo and can see the display working.

This is my first time doing one of these repairs so my apologies for anything stupid I say or anything obvious I miss

Board is 820-3330-B.

F9700 is showing 3.3V on both sides of the fuse, I believe it should be 12.6V?

Now I have got stuck, what can I inspect next?

Many thanks.

[mon2]

Re: MacBook Pro A1286 Mid 2012 no backlight but display working

So PPBUS_G3H = 3v3 ? This is not correct for a good board.

Check for the presence of fuses @ F7040 & F7041.

Remove all power. Meter in resistance mode (lowest scale).

Check for the resistance to ground @ F7040, pin #1 or # 2.

We are checking to see if you have a low resistance = bad cap on this rail ?

If the resistance is not too low, remove F7040 & F7041 (if present) off the logic board. Then power up again.

Check the voltage of PPBUS_G3H @ F7040, pad # 1 on the logic board.

Do you see a higher voltage for PPBUS_G3H ? Post your readings.

[Gigabit2]

Re: MacBook Pro A1286 Mid 2012 no backlight but display working

Am seeing 12.5V after removing F7040 and F7041

[mon2]

Re: MacBook Pro A1286 Mid 2012 no backlight but display working

Remove all power. Meter in resistance mode.

Check for the resistance to ground @ F7040, pin # 2 (the other side of this fuse) = consumer side. We know that pin # 1 of this fuse = producer side is OK.

Red lead on this pad; black meter lead to ground.

What is the resistance ?

So far, we know that U7000 is OK.

[Gigabit2]

Re: MacBook Pro A1286 Mid 2012 no backlight but display working

Resistance showing 1 . on multimeter display with lowest scale set.

[mon2]

Re: MacBook Pro A1286 Mid 2012 no backlight but display working

That likely means that the scale is too low to measure the resistance.

Increase the scale till you have a reading. Then post the scale setting and reading.

[Gigabit2]

Re: MacBook Pro A1286 Mid 2012 no backlight but display working

With scale at 2M, seeing .046 on pin 2

[Gigabit2]

Re: MacBook Pro A1286 Mid 2012 no backlight but display working

Hi @mon2 is the above enough info

[mon2]

Re: MacBook Pro A1286 Mid 2012 no backlight but display working

Yes. The resistance looks ok.

Install back the fuses @ F7040 & F7041.

Remove the fuse @ F9700 (backlight fuse).

Power up again. What voltage do you read @ F7040, pin # 2 ?

Confirm that the same voltage appears at the removed F9700, pin # 1 pad.