820-3115-B low PPBUS_G3H

[Sr. Robot]

Got an 820-3115-B with 1.4v on PPBUS_G3H.

PP3V42_G3H is 3.7v and PP5V_S3 is 0v.

CPU is getting hot. Removed removed Q7510, Q7520, Q7550 and Q7560 but CPU still getting hot.

 

[2informaticos]

Did you check diode mode to ground at PPBUS_G3H?
Possibly one high-side MOSFET from CPU power supply is fried.

 

[Sr. Robot]

PPBUS_G3H is shorted. Diode mode is 0

 

[2informaticos]

Check Q7510/20 and Q7550/60; at least one is shorted.

 

[Sr. Robot]

I removed one by one and checked CPU surface. Maybe 2 are shorted? Is there any other way of knowing ?

 

[2informaticos]

When (if) the short disappeared from PPBUS_G3H?

 

[Sr. Robot]

The short was in Q7550. After replacing it the mac turned on for about 10min then shut down. Q7550 is shorted again. Charger and battery are originals. What could be causing this?

 

[2informaticos]

Replace C7551.
Be sure R7551/55 have correct values.
Also check all adjacent traces and solders.