MacBook Pro A1707 Motherboard Diagnostic Help – CD3215 heating and Fluctuating Rails

[Cemal Odabasioglu]

Hello everyone,

I'm currently diagnosing a MacBook Pro A1707 motherboard that does not power on. I've gathered some data but am stuck and need expert advice.
Note that i'm a beginner in electronics and i'm trying to learn while trying to repair this macbook that my work gave me. I'm really curious and love understanding how thing works and i already learned so much.

Only one usb c port is taking 20v and have 12.5v on PPBUS_G3H. when trying other ports, 2 are not going to 20v and one is going to 20v but the CD3215 is getting really hot.

Observations and Measurements with the working usb c port

1. Power Rail Voltages:

PPBUS_G3H: Stable at 12.5V.

PP3V3_UPC_TA_LDO: Stable at 3.3V.

PP1V8_UPC_TA_LDOD/A: Stable at 1.8V.

PPDCIN_G3H: Stable at 20V.

PP1V1_UPC_TA_LDO_BMC: Measured 3.3V (expected 1.1V – abnormal).

UPC_TA_GATE2: Measured 0V

PP3V3_S5, PP5V_S5, PP3V3_S4, PP1V8_S4: All fluctuating rapidly (not stable).
PP3V3_s5 -> fluctuating rapidly no short
PP5V_s5 -> fluctuating rapidly no short
pp3V3_S4 -> fluctuating 0-0.3v no short
PP1V8_s4 -> fluctuating 0.01v
PP5V_s4 -> 0.0v no short
PP1V8_S3 -> 0.01v fluctating no short
PP5V_S0 -> 0.17 - 0.30v fluctuating no short



2. Resistance Testing:

I measured 18 ohms to ground on C3108 (seems low for a 3.3V rail) near the CD3215 that was heating
I've inspected the capacitor physically, but no visible damage is present.



3. CD3215 Behavior:

When the charger is connected to a specific USB-C port, one of the CD3215 chips heats up more than usual.

On other ports, the chip does not heat excessively.
On the working port, that one chip is heating but not like the other who was getting really hot


4. Amperage:

The board draws ~0.03A on the charger, which is far below normal.



5. Miscellaneous:

I've checked for shorts on the fluctuating rails (PP3V3_S5, PP5V_S5, etc.), but no obvious shorts were found.

The fluctuating voltage on the S5/S4/S0 rails suggests an issue with power sequencing or load.





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Questions:

1. Is 18 ohms to ground on c3108 considered abnormal? Could this be caused by the CD3215 that was heating?


2. Could the fluctuating S5/S4/S0 rails be related to a failing CD3215 (the one that is getting a little hot)?


3. With 12.5V on PPBUS_G3H, is it safe to assume the CD3215 chips are at least partially functional?


4. Should I try removing the CD3215 chip that heats up to see if the PP1V1_UPC_TA_LDO_BMC rail becomes ok?


Thank you in advance for any guidance or advice you can provide!

[mon2]

PP1V1_UPC_TA_LDO_BMC: Measured 3.3V (expected 1.1V – abnormal).

Yes. This, to me, is a defective PD controller or.... Yet, this port is working? Would you have fresh batteries in your multimeter? For the 20v power delivery contract to be negotiated, the BMC line must be working to properly communicate with the external power delivery (PD) power adapter. This is working since you have 20v.

Flux and remove C3108. Then measure the resistance to ground again on PP3V3_UPC_XA_LDO to confirm if there is a much higher resistance to ground than 18 ohms.

[Cemal Odabasioglu]

Thanks for your response, i actually don't get it, after retrying to measure voltages i get all LDOs except the pp1v1_upc_ta_ldo_bmc (0v) but i get 20v 0.06 amps on charger ! If i have 0v on that pin i shouldn't get 20v right? And all the cd3215s are not working properly but i get 20v on charger on a specific port how is that even possible because all CD3215s should work properly in order to make a communication between all of them and get 20v on charger, that's what i've read. I'm actually really confused. I don't know what to do actually any help will be really appreciated.

[mon2]

pp1v1_upc_ta_ldo_bmc (0v)

This LDO rail will only be active provided that side of the USB-C connector is used as the active port. If you have 20v on the PD rail then the PD contracts have been negotiated correctly.

[Cemal Odabasioglu]

Ok, so the problem is not the cd3215s. But i have fluctuating pp3v3_s5 and pp5v_s5, etc...
What should i check now? Who can be the culprit?

[mon2]

Remove all power. Meter in resistance mode. For each voltage rail that is not stable, measure the resistance to ground of that rail. Post each measurement in ohms.

If there is a lower than normal resistance on that rail then there is most likely a shorted component that needs to be removed or replaced.