820-00165 short on PPBUS_G3H

[waseem345]

Hi everyone,

I have an 820-00165, the board looks new and has a green light but no power.

noticed that F7140 has 8.6v on pin 1 but 0v on Pin 2, I can also see that there is short to ground on pin 2.

I just bought myself a power supply and connected black wire to the screw hole and red to pin 2 (f7140 removed), on the power supply itself I can only increase the amps, set the amps to 5 and voltage went to 0.85v. What am i doing wrong here?

 

[JohnB8812]

It's pulling power because something is shorted it's working fine. Inspect all of the tantalum caps for cracks and or ooze coming out of them it is very common for the ones above the fan FPC to crack or go bad as well as ones in the center of the board. For future reference, it is always best to start at 1 volt in case the CPU is shorted. Something must absolutely be getting hot tho at 5 amps.

 

[waseem345]

The power supply is only injecting 0.85v, nothing is getting hot. All caps look perfect, that's why I'm so confused.

 

[JohnB8812]

Remove the CPU heatsink. See if the CPU die heats first. You can increase voltage to more than 0.85 volts if it doesn't usually around 3-5 volts, one of the caps will show itself.

 

[waseem345]

How do i increase volts?, on my power supply it wont let me increase volts, only amps

 

[waseem345]

cpu isnt hot (heatsink removed

 

[JohnB8812]

Pretty sure the button in the middle is two switch from amps to voltage. 5 volts 3 amps should find the short without any issue.

 

[2informaticos]

Check resistance to ground from all big coils.
Compare which is closest to PPBUS_G3H to ground.
NEVER ever inject tension before you check NO high-side MOSFET is shorted.
If not, you risk to inject overvoltage on CPU, or other sensitive component...

 

[waseem345]

I was able to find the shorted cap and now macbook powers on, however can anyone tell me why I can only change the amps on my power supply and not the volts, is it my power supply that is faulty? btw the middle button is to stop the output.