Today I plugged in a monitor to the C5 to see what happened when I loaded a programme from MFI.
I also tried to save the programme to Floppy Disc.
The commands used for the FDD are the same as those used fir Tape.
The Monitor has the information Save to Disk, Erase and load from Disk.
The word Disk must programmed into the video EPROM so I now know that the instructions are the same.
However the Disk (disc) drive does nothing and alarms appear both on the machine and repeated on the monitor.
I am beginning to wonder if someone has in the past changed something on the interface to FDD board.
As I have mentioned before there is no 5 Volt supply to the FDD or any of the chips on the interface card.
There is a power transistor on the interface board but I would have expected to see a fixed 5 volt regulator.
One mystery solved but another one to solve.