820-4924 no brain?


New member
The macbook turns on cpu heats up and fan spins but no chime no image nothing on external monitor. I use a backlit keyboard to test machines to see if theyre at least booting on these ocassions but it doesnt even light up. My guess is that its brain dead but cpu is present at 1.8v so not sure what it could be.


New member
Light on USB mouse? If yes, check for voltage to the screen. If no, check if PLT_RESET_L is 3.3 volts. If so this is trash. If not 3.3, we’ll go from there.


New member
my only usb mouse got mauled apparently but i do have a usb amp meter and it powers on. PLT_RESET_L is 3.3v

pin 3 and 4 of j8300 get 5v the rest gets nothing.
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Staff member
USB mouse is tricky sometime.
Always better to test with OSX pendrive.
If link LED flashes, then USB activity is 100% confirmed...

Pins 5 & 28-30 should get voltage at least first few seconds.
Voltage drops if pin 9 doesn't go high.


New member
no image theres no brain otherwise my keyboard would have lit up. this keyboard i have only lights up when a chime would be present. i even changed out bios and nothing. im assuming its a bad cpu/pch.