MP is version 1.2.1 with MAV 1.0, MinimOSD flashed with the Jun 1st release of the MCM and HEX files (multiple times with the FTDI cable from DIY drones).
2 stage power, 12V (cooled by a fan) and the 5V from APM2.
Wiring is confirmed correct.
No micro USB cable is connected.
MP telemetry is just fine, it responds to tilting of the APM2.
I am using a 3DR 900Mhz radio for telemetry.
I suspect something with the character set update, but nothing looks suspicious.