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This MacBook originally showed a short on PPBUS, which I traced to one of the CPU power drivers (U7410). Replacing it removed the short. Now the trackpad clicks and the fans are spinning, but it doesn't start up. PPBUS is 12.57V and the USB-C meter reads 20V and 2-3A (without a battery...

If a trace is broken it must be inside the board. I could remove the two troublemaker CD3215s and check for continuity of the connections between XA and XB. Any pointers as to which lines are the important ones? I2C_UPC_XA_DBG_CTL? I2C_UPC_X?

After replacing all four CD3215s, the situation is unchanged. One additional observation is that the bus connecting the CD3215s together (I2C_UPC_) shows values around 2V on half of the CD3215s, and 3.3V on the others. Help!

Yes, both ways. Note that I have replaced several CD3215s, all sourced from various donor boards. I now suspect that some of these were not fully functional to begin with... I will get brand-new CD3215s and replace all 4. Stay tuned.

Also, I got the machine to start up on battery power. It shows the battery percentage but does not recognize the charger at all. The battery is not charging.

Another observation: when I connect a battery, I get the following depending which port I plug the charger in: TA: 20V 0A TB: 20V 0A XA: blank USB meter XB: 20V 0A Without a battery present, I get: TA: 5.1V 0.26A TB: 5.1V 0.26A XA: 5.1V 0.26A XB: 5.1V 0.26A

Is power to U2800 needed for the CD3215s to work? I noticed an asymmetry between these rails (on a good board these values are all the same): PP20V_USBC_XA_VBUS: 0.18 PP20V_USBC_XB_VBUS: 0.14 PP20V_USBC_TA_VBUS: 0.18 PP20V_USBC_TB_VBUS: 0.14

Waiting to hear if there is anything else to try before giving up on this board?

I replaced UB300 and that fixed this issue. I now have 20V on all 4 ports.

Replaced ROM chip U2890 from donor board, with no change.

As stated before, resistors round U3100 check out ok. The only differences between J3300 and JB500 are the DBG lines on J3300 (which I think are not supposed to be there on JB500).

Yes, I know. Where do I look next?

Here is a summary of the asymmetry that I find between the XB and XA ports: XB readings when plugged into XB: PP1V1_UPC: 1.1 CC1: 1.7 CC2: 0 XB readings when plugged into XA: PP1V1_UPC: 0 CC1: fluctuating CC2: fluctuating XA readings when plugged into XA: PP1V1_UPC: 0 CC1: 0 CC2: 1.8 XA...

Yes, charger works both ways but gets only 5V 0.26A. Resistors all check out correct.

I already replaced the CD3215 twice with no change.

Board had minor liquid exposure in the USB-C area of the XA port. PPBUS was 80Ω to ground. I found a shorted speaker amp (U6550) and replacing it removed the short on PPBUS. I replaced all components with possible corrosion in the USB-C area around U3100, including the CD3215. Now, all 4 ports...

Yes, both sides of RB630/640 show the same diode mode readings as for the other 3 ports. I also checked on a separate board and they are the same, also.

It's the TA channel. I could replace UB300 but I'd like to first know where the fault lies und understand the behavior.

Strangely, all pins on both connectors show exactly the same readings in diode mode. There was a small amount of liquid in the area around the CD3215s (UB400 and UB300) but no visible damage.

CC1 and CC2 lines have the same diode mode readings as the other ports.