Re: db-19 cables from older Mac 400K 3.5" drives

[dempson@actrix.gen.nz (David Empson)]

stephen e buggie <buggie@argo.unm.edu> wrote:

>                DB-19 ROUND CABLES FROM OLDER MAC 400k SINGLE-SIDED DRIVES
> 
>                THESE CABLES SOMETIMES WORK WITH A2; SOMETIMES NOT: WHY?
> 
> 
> 
> 
>       Occasionally, I salvage an older Mac 400K single-sided external
> 3.5" disk drive at a flea market or yard sale.  This drive is TOTALLY
> INCOMPATIBLE with A2, and must not be connected to any Apple II.

Not quite true - I've heard that they will work with a Universal Disk
Controller card.  Even then, they are of somewhat limited use, because
very little software is supplied on single sided 3.5" disks.  It would
still be usable for data storage and exchange (provided the disks were
formatted as single sided).

>       I once did pin-out measurements on this short db-19 cable and
> found them to be the same as with Apple II db-19 cables.
>
>       I've connected this short Mac db-19 cable to Apple Disk II drives.
> About half the time, the drive works perfectly.  Yet, with half the short
> cables, the drive does not work well.

It is possible that not all cables are identical.  They may have
eliminated unused wires in some cables.  The Apple 3.5 Drive on an Apple
II uses more signals than the 400K/800K/Apple 3.5 on a Mac.

However if they just work unreliably (as opposed to either perfectly or
not at all), this isn't likely to be the problem.

> My _hunch_ is that possibly the male pins on the db-19 plug may be
> slightly thin, and some do not make good contact with the walls of the
> female db-19 socket.

That sounds a little dubious, but not beyond the bounds of possibility.
It could be a noise/shielding problem.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand