Unlike other Roomba models, for the s9 there is little to no information available for setting up and using a serial connection to a Windows PC.
I've managed to get to the point where Putty serial can connect to the device on COM5 at 115200 baud. But with the Roomba appearing to be awake, no text comes across at all on the session, even when the device is put into diagnostics mode or rebooted.
Could this be a driver issue? Or, and indication that the motherboard is toast?