CD3215 Bootup Sequence
Getting 20V on the charger
If a CD3215 does not have the LDO outputs, test the lines for shorts, otherwise the chip is missing power or bad. Data sheet of closest Ti chip.
A bad CD3215 can often cause a loop at step 10. All of the CD3215s need to be fully functional and communicate with the SMC before the CD3215 connected to the charger will request 20V.
The TBT ROM is required to get to 20V. It is powered by the CD3215 on the opposite side. It will not boot unless it can communicate. It seems with liquid in that area, the trace between the LDO of the CD3215 and TBT ROM gets damaged at the test point. Without communication with the TBT ROM, the 1.1V BMC LDO won't come up while other LDOs will be present. The 1.1V BMC LDO is used to drive the logic negotiating USB-PD. When that happens, when USB-C is connected to this CD3215, it will not negotiate 20V and get stuck on 5V, not cycling.
When one CD3215 in the system is bad, it will often cause others to not work as well, and they will often be power cycling after starting USB-PD negotiation as a result.
The CD3215 in one pair work in a master-slave fashion. For example on 820-00281, U3200 is the master while U3100 is the slave. The master is connected directly to the TBT ROM (U2890), while the slave (U3100) reads the TBT ROM firmware through the master (U3200). As a result, if the master (U3200) is not working properly, the slave (U3100) won't work either.
Please note, the chip designations and net names are from an A1706.
|Step||Source||Name of Net||Voltage|
|3||U3200||HV_GATE1||High(5v, later 20V)|
|U3200||HV_GATE2||High(5v, later 20V)|
|6||U7000||PM_EN_P3V3_G3H||3.3V (5V on many boards)|
|11||U3200||USB_XB_CC1||0.8V (data) (verify)|
|U3200||USB_XB_CC2||0.8V (data) (verify)|
|17||U7000||Q7030 Q7040 opening||Unknown (low maybe)|
Thunderbolt ROM is required to get 20V.
If you get a message saying Critical Update Required there may be a problem with the logic board.
Piernov 11.8.2020 at 9:29 AM
@ChrisB [VA, US] U3100/U3200 were 5V not cycling. U3200 was missing 1.1V BMC LDO. U3100 is missing it too, however it's the slave so it gets the TBT firmware through U3200 so that's normal. (I'm not sure if the slave could cause the master to have missing 1.1V BMC LDO though) At one point U3200 3.3V LDO was sending out 4.2V, so that was going to the TBT ROM (U2890) as well, I doubt it damaged it but it's a possibility. UB300 and UB400 were power cycling with 1.1V BMC LDO present, so they seem to be working fine, cycling being caused by the other pair.
Issue: 820-00840 wont take anything from charger, either port, or orientation.
Visible inspection resulted in marks on CC1/2 pins on both USB-C ports.
Diode mode measurement showed ~0.550V on 3 of them, one ~0.040V.
Replacing the port fixed the issue.
Conclusion: One damaged CC pin can cause the whole lot to stop functioning.