won't power on with button, CAN reset SMC with button, can power down

this particular MacBook has me scratching my head.

as mentioned, it's mid2012 A1278 base spec, and the machine will NOT power on from the power button. if i yank the battery and connect the magsafe, it fires right up.

when powered off i can reset SMC with the power button, or at least the magsafe indicates that i can. i've attempted multiple SMC and NVRAM resets.

once the machine is powered on, i can initiate sleep or shutdown using the power button.

I have pulled this MLB and put in another functioning mac, with the same result so I'm confident it's the one MLB and not two keyboards.

anybody have any experience with this?

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just for $@$** and giggles, i amazon sameday'd a replacement keyboard (brand new). same story, can't power on from button. can't seem to power on with pads either.

if i remove the battery and connect the magsafe, it will fire up. in this configuration, it will not stay off if i power it down, it simply fires right back up.

i welcome your thoughts!!!!!!


Id check the board with a multimeter. Sounds like an issue with SMC_ONOFF or U5010 Area. Id like to check what happens when you press the power button. When the machine is off yet plugged into power do you get 3.3V on the Power on pads?


Thanks! I’ll check that and report back in the morning. I have the board view for this but I’m not an accomplished troubleshooter.


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