We were not getting any sector pulses from the 77 track Micropolis drive. The 7414 inverter probably has a leaky input and is pulling the input signal from the sector phototransistor just a little low so it does not trigger the 7414. We added a stronger pullup to +5V on the input of the 7414 and the drive now works. We ordered some 7414 parts and will replace it next week.

Mike Douglas made a 35 track MDOS image, and 35 and 77 track CP/M images for the Altair with a Micropolis diskette controller. We will give CP/M a try next week.