Most of the embarrassment has faded away, so I can write about it now. Having my Cubieboard up and running I went for the next step, connecting my TNC for APRS operation. The Cubieboard has a UART port, but the supplied cable was for a USB connection. I still had my serial converter from my Raspberry Pi and tried to hook it up to the Cubieboard. Either I made a short or some Volts went where they shouldn’t have gone, but all of a sudden there was smoke and that is usually not a good sign.
So now I have two empty cases on my shelf: one for the Raspberry Pi, one for the Cubieboard. Ah well, that’s life. Luckily these mini-PCs are not expensive, but to me also not cheap, so I will wait a while before ordering another.