fixit9660
Member
Well, good news; after some significant help from Stuart last night, and overcoming a schoolboy error on my part, I now have a working disk system. There were several problems though. The first was power; whilst being powered from the Cortex PSU the disk activity failed. Change to the disk system stand-alone power supply and it worked, but only Reading from the disk. The difference in power supplies is minimal, Cortex PSU 11.6v and 5.2v, Disk PSU 11.8v and 5.0v, but obviously enough to make a difference. I'll be diving deeper into the Cortex PSU power distribution soon to determine why. But as I said further investigation revealed that this only got the disk Reading working, Writing/Formatting was still not working. It further transpired that IC63, (IC6 on my motherboard), an SN74LS07 Hex Buffer/Driver, was showing the WRITE GATE signal on the actual Pin 2 of IC63, but it wasn't making it onto the motherboard via the socket!! Some judicious pin bending on the IC gave the required pressure to give a good contact and hey presto Writing/Formatting. It highlights the variability of the reliability of cheap flat/stamped sockets over the more expensive turned pin, phosphor-bronze insert type. I'll be replacing the socket with said turned pin type as soon as possible.
It just re-enforces the "fresh pair of eyes" situation can be so helpful when you are stuck. Familiarity with the CDOS syntax, as well as having another, working, Cortex and disks to swap with was also invaluable. Many thanks to Stuart!!!!
Besides making a DISKCOPY of the CDOS disk, I've now managed to create two working CDOS floppy disks from scratch using the prescribed method and PC CommsUtil; would you like one? Happy to post one.
Looking at your symptoms above, have you checked that the various signals to/from the Floppy Drive are visible on the 9909 IC and the various buffer chips IC83, 84 and 85 to/from the Floppy Drive? I've attached the schematic that covers the circuitry involved.
It just re-enforces the "fresh pair of eyes" situation can be so helpful when you are stuck. Familiarity with the CDOS syntax, as well as having another, working, Cortex and disks to swap with was also invaluable. Many thanks to Stuart!!!!

Besides making a DISKCOPY of the CDOS disk, I've now managed to create two working CDOS floppy disks from scratch using the prescribed method and PC CommsUtil; would you like one? Happy to post one.
Looking at your symptoms above, have you checked that the various signals to/from the Floppy Drive are visible on the 9909 IC and the various buffer chips IC83, 84 and 85 to/from the Floppy Drive? I've attached the schematic that covers the circuitry involved.