Macbook Pro 13 A1278 - cycling PPBUS_G3H

[Adenitz]

Hello guys,

I have a board from year 2011. History unknown. I have only board and PSU. I was told that Macbook starts and shutdown and battery is not charging.

I have steady 3.42V voltage and green light on charger (PP3V42_G3H = 3.48V). However PPBUS_G3H cycle between 12.9V (already too high) and 3.5V. The time priod of cycling is about 5sec. PPBUS_G3H keeps at the level of 12.9 for about 5 sec, and there is gradual drop to 3.5V and then back to 12.9V (in about 3-4 sec).

In the repair wiki, I couldn't find what could be the problem. I suspect that U7000 chip ISL6259 could be bad, but wonder how can I be sure.
CHGR_ACIN is about 3.5V

Should i remove the fuse F7040 and test whether the problem is on the generating PPBUS_G3H side or futher in the circuit?

[mon2]

Re: Macbook Pro 13 A1278 - cycling PPBUS_G3H

Hi.

Is the power adapter the original and suitable for this logic board?

Yes, remove the fuse and confirm if the power rail remains stable without the downstream load.

Based on the long duration of pulsing at every 5 seconds, it likely is not a shorted cap fault.

Could be bios communication fault. Check the voltages of your bios device onboard.

[Adenitz]

Re: Macbook Pro 13 A1278 - cycling PPBUS_G3H

Hello mon2 and thank you for your help.

Is the power adapter the original and suitable for this logic board?

No, I don't have a charger. I have lab PSU set to 15V and Magsafe connector (L style) connected to the PSU.

Could be bios communication fault. Check the voltages of your bios device onboard.

SPI ROM (U6100):
PIN1: 3.29V stable
PIN2: 3.29V stable
PIN3: 3.3V for about 6sec then 0 V for about 3 sec then back to 3.3V and so on.
PIN4: 0V stable
PIN5: 3.29V cycling (6 sec 3.29V and then 0V for about 3 sec)
PIN6: cycling same as PIN5
PIN7: 0V stable
PIN8 (3V3_S5): cycling same as PIN5

I'll check PPBUS_G3H after removing the fuse and let you know.

[mon2]

Re: Macbook Pro 13 A1278 - cycling PPBUS_G3H

See attached.

Check & post the voltage readings on the SMBUS interface lines. Invested about 8 hours a few weeks ago to locate that the same ESD diode (D6950 = tiny little bugger) was the fault. Client had to play roulette as to when the laptop would turn on.

Interested in the voltages at these 2 lines. These same interface lines are used to chat with the battery and U7000 (perhaps other parts on the logic board as well).

[Adenitz]

Re: Macbook Pro 13 A1278 - cycling PPBUS_G3H

Thank you mon2, I'll check this when I get back to this board, currently doing another job.
BTW I have removed the fuse, and on the system side was about -0.3V, but on the side towards U7000, it was still cycling from 3.5 to 12.97V.