Troubleshooting a V20-MBC connection issue
At some point, with the V20-MBC, starting Minicom did nothing and only the terminal printed its signon messages. The remote device wouldn't boot and there were no signs of life other than the lit LEDs.
The flat cable that runs from the V20-MBC ends in a serial-USB adapter with a USB connector that goes into the Chromebox. This is the adapter card with the USB connector at left and, at right, the pins the cable's connector plugs into:
To troubleshoot the issue I unplugged the USB connector from the Chromebox, which is when the cable's connector came out from the pins. That made clear the issue was a loose plug. Plugging the adapter back into the cable, reconnecting to the Chromebox, and starting Minicom made the V20-MBC automatically boot up as usual.