Moon 350P input selector skipping digital inputs

Just bought a Simaudio 350P preamp on Audiogon with the digital and phono stage optional boards. When cycling through inputs, until shows cd, a1, a2, ph, b1, b2. But instead of walking through d1, d2, d3, d4, the input selector skips back to cd.

Checked that the digital board is installed and all connections are solid. Digital source connected to unit via USB recognizes it as 350P.

Is there some kind of reset that will make the digital inputs show up?