Thanks for your reply.
The interface board is both complex and has mainly Surface Mounted Devices (SMD) so they are small.
The floppy seems to be OK when connected to a normal PC.
There is no 5V supply on the interface but neither is there a connection to the 5v rail as there is in the drawings for the tape.
All the other wires are exactly the same as the tape drive.
Pins 9 and 12 are not connected to anything on the interface board.
I have not worked out how the 5V supply is derived but it must be on the interface from the 16 volt rail.
Later today I will have another look and see if I can do some measurements.