Hi got a secondhand Minitaur a long while back and haven’t noticed until today that C1 does not fire. Is this a known issue? v2.2 firmware installed. The incoming midi LED (under the hoof) lights up but neither of the oscillator audibly fires. Adjacent notes B0 and C#1 are ok… 
Have you tried a different keyboard? Or playing it via a MIDI file, if you don’t have a different keyboard available?
If this does not play this note, you might have to use the Note Calibration function. You start this via a MIDI SysEx file.
The latest firmware is 2.2.1