Lenovo Yoga 910 with NM-a901 board

[Lukosiukas]

Hello, I need advice, computer turns on only with battery plugged in and usbc charger, but charger stays in 5v mode and 2.4-2.5A, does not switch to 20v, by that, GPU core does not start. I know computer starts because it goes to sleep after pressing button, pressing caps lock turns on the light. I have all power rails present, no shorts, no liquid damage. How board communicates with charger and tells to turn on 20v mode? Thanks in advance.

Attaching schematic.

MOD Edit: Link to schematic - https://www.badcaps.net/forum/showthread.php?t=81087

Reminder, rules and organization of this section - https://www.badcaps.net/forum/showthread.php?t=117483
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[mon2]

Re: Lenovo Yoga 910 with NM-a901 board

1) The schematic should only be posted in the schematic forum. If possible, do move your attachment to the dedicated forum but link it here for future readers.

2) The power adapter is a type C adapter. So this is an intelligent power supply that works by advertising a database of power delivery packets (voltage & current). The host logic board will extract this database upon docking and then will select the best suited power delivery contract after this handshake.

3) The communication for these power delivery contracts is performed over the CCx lines. There is CC1 on one side of the USB C blade and then CC2 on the other side. It is a single wire interface that uses BMC to chat between host and slave devices.

Using a USB C PD bus analyzer, you can view the handshakes with the power adapter. There are low cost tools from Aliexpress stores that can show you the gory details. The better tools are from Cypress and LeCroy but will be at a higher cost.

4) The PD controller is a stand alone device on your logic board and sometimes, it loses the firmware / gets damaged. Respectively, the mfr of the logic board should offer a solution to reflash a virgin PD controller IC.