Hi all, hi Peter,
Thank you for your feedback. The answer to Peter K's question first:
The spindle motors in the 8" drives rotate all the time, but the read/write heads only snap together towards the floppy disk ("loading the heads") before every read/write access. They are lifted off the medium right thereafter again to reduce wear.
8" drives had a signal input "-head load" to control this; newer drives don't.
They still have a "-motor on" signal - but spinning up takes ~10x longer than loading the heads. After the CMI II tells the drive to get ready ("-head load" now!), it doesn't wait sufficiently long for you to connect that signal to "-motor on" at the drive and hope it would have spun up in time.
I actually tried it - and can confirm that simply using "-motor on" as "-head load" replacement would definitely lead to read or write errors.
So what has to be done, is keep "-motor on" permanently active, and leave everything else to the logic inside the drive.
A given drive may or may not control head loading internally - if yours doesn't, the head may contact the medium all the time, with the spindle motor spinning all the time. (Some drives might evaluate "drive select" etc. to make their internal decisions.)
But actually, multiple people who replaced 8" drives by 5,25" or 3,5" drives (on other computers, for some time) reported no symptoms of floppy wear nor real life reliability problems.
AFAIK, the CMI III QFC9 could have ROMs for either older or newer drives - I guess the newer version knows it's using "-motor on" and therefore has to wait longer, so it can allow the (rarely used anyway) drive to spin down when not in use. It might be possible to find a patch for the II/IIx ROM and also use "-motor on" thereafter, but I haven't spent the time.
That's for the tiny limitation.
--
Now, what the actual solution needs:
- An adaptor that connects the signals from the 50pin controller connector (or cable) to the 34pin floppy drive connector in a proper way. Can be for both drives, what I made, or one drive per adaptor, what Fairlight has made for the CMI III. These are all just cables/signal lines, no other parts, and easily prepared.
- A simple power supply connector for each floppy drive (CAVE: the CMI power supply also provides 125V or 250V for the old drives!). Can be homemade from PC parts, but a Fairlight (?) part exists as well.
- Floppy drives which do/can deliver the "-ready" signal. Finding one (or two) of these may be the difficult exercise. Even sub(!)-model-numbers from renowned makers like TEAC differ as to availability of configuration jumpers, but many drives can be modded to provide the signal even if no jumpers are available.
I just had started to write it up more from memory in this reply... But the story got too long. So please allow me some time and I'll put my background info, photos, list of suitable drives etc. to my WWW in a proper manner.
Cheers, Joerg
--- In Fairlight-CMI@yahoogroups.com, "Peter K." <synthserv@...> wrote:
>
> Just wondering What is this "one tiny limitation from technical perfection"?