Power issue on a MacBook Pro A2485 (motherboard: 820-02100-A)

[datatech85]

Hello,

We received a Macbook pro A2485 which has a power issue. Battery doesn’t take charge and all the USB C ports are stucked at 5V / 0.018A. We can’t get 20V.

The Macbook has already been to a repair company and we note that the UG400 chip has been unsoldered.

Here are the operations we have carried out:

- Replacement of the CD3217B12 chip “UG400”. We know that this type of chip is programmable and that it's essential to have a chip from an identical motherboard in the same position. We found this chip on Aliexpress, which comes from the same motherboard.

- Voltage measurement across fuses F5200 and F5201 = 0.23V

- Voltage measurement on the PPVBAT_AON_CHGR_REG rail when the fuses F5200 and F5201 are removed = 12V

- Voltage measurement on the power rails of the CD3217B12 “UG400” chip (Result attached)

We assume that the USB C chip we replaced is possibly dysfunctional but we would like to be sure before ordering a motherboard.

Do you have any other leads on the origin of the failure?

Thanks in advance,

 

[2informaticos]

As per names, UG400 is paired with JG600.
Is irrelevant to cheack voltages on UG400 connecting the charger to JF600.

Check diode mode to ground at PPBUS_AON and 3V8_AON power rails.

Any history available?

 

[datatech85]

Thanks for your answer.

I checked in diode mode PPBUS_AON and PP3V8_AON power rail.
It seems that both rails are shorted (or at least low resistance).
I've got 26,7Ω on PPBUS_AON and 29,5Ω on PP3V8_AON.

Regarding the history, we don't have any informations on the operations carried out by the previous repair company.

Any leads ?

 

[2informaticos]

I hope you've disconnected charger and battery, before checking in diode mode.
Now check resistance (ohm scale) between PPBUS_AON and 3V8_AON (not to ground).

 

[datatech85]

Yes, battery and charger were disconnected.
I've got 30,1ohm between PPBUS_AON and PP3V8_AON.

 

[2informaticos]

That's strange.
Seems to have problems on both power rails.
Check if any big coil gives same reading to ground as PPBUS_AON.
Don't forget LN480/980.

Use ohm scale, as always for low readings.