internal short cut - 820-02935 -A2992 - macbook pro 16" m3 max

[defdjamel]

820-02935 - a2992 - macbook pro 16" m3 max
Laptop: 5V - 0A

Issue: PPBUS_AON_SPKRAMP_ABC and PPBUS_AON shorted.

• On PPBUS_AON_SPKRAMP_ABC, capacitor CR635 was damaged (melted) and created an internal short circuit to ground.
• I removed faulty components (CR635, CR634, CR633) and also chip UR630.
• Result:
  • PPBUS_AON_SPKRAMP_ABC → still shorted
  • PPBUS_AON → still shorted

When I inject 3 V / 1 A on PPBUS_AON_SPKRAMP_ABC, heating occurs on pad CR635.

I suspect that during the failure, the pad and line PPBUS_AON_SPKRAMP_ABC melted into ground( i try to fix, but its the mess, i don't want to damage more...)

So, I decided to cut the line between PPBUS_AON and PPBUS_AON_SPKRAMP_ABC at RD698.

• After that:
  • Laptop starts with 20 V - 0.17 A, but reboots in a loop.
  • PPBUS_AON → OK now
  • PPBUS_AON_SPKRAMP_ABC → shorted to ground(normal)

I measured PPBUS_AON_SPKRAMP_ABC and I have 3 V, even though it is isolated from PPBUS_AON.( resitance PPBUS_AON to PPBUS_AON_SPKRAMP_ABC = OL)

👉 Question: Where could these 3 V on PPBUS_AON_SPKRAMP_ABC be coming from?

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My idea / next step:

• Isolate the 3 speaker amplifiers (UR600, UR630, UR660) by cutting the line PPBUS_AON_SPKRAMP_ABC, and create a new PPBUS_AON feed before the short.
• Apply the same method with the ceramic capacitors (CR800 → CR807).

Thanks in advance, it’s a very interesting case.

[mon2]

The boot loop can be triggered due to the now missing current sense circuit @ UD610. That is, this current sense circuit is able to see that PPBUS_AON is present but does not leave across the RD698 resistor. The current sense IC @ UD610 is expecting to measure the small voltage drop to gauge the current draw of the load = the audio amplifier leg. When it observes there is 0v on the opposite side of RD698, the logic board cycles.

[defdjamel]

Thanks mon2, UD610 is not present PPBUS_AON and PPBUS_AON_SPKRAMP_ABC are simply shorted in this logic board.. RD698 is a short i will send you a picture.
that will not explain the 3V on PPBUS_AON_SPKRAMP_ABC maybe this line is shorted with other line....

[mon2]

Suggest to flux and use solder braid to clean up this current sense resistor pads. Then use IPA to remove all remaining flux to confirm the area is clean and isolated.