db-19 drive cable compatibility: A2 vs Mac

[buggie@musca.unm.edu (stephen e buggie)]

      COMPATIBILITY EXPERIMENTS OF APPLE II VS. EARLY MAC
                    DB-19 DISK DRIVE CABLES


	I've been scrounging db-19 cables to retrofit onto my sensational
enhanced Disk II 5.25 drives ("Bugg-Drive").  The db-19 is the round cable
that is directly compatible with the IIgs, IIc+, and IIc.  The standard
Disk II cable is the traditional old flat ribbon cable with IDE-20
twin-row connector.  The ribbon cable _can_ be used witn the IIgs, but the
Disk II interface card must be used --- and it occupies a slot.  The
IDE-ribbon cable can work with the IIc+ or IIc with a special adaptor by
Pico (formerly sold by Jameco Electronics but no longer available).  The
best solution is to attach a db-19 cable to the enhanced Disk II, but
these cables are scarce!

	Two years ago, I successfully ran a Disk II drive from a beige
db-19 cable salvaged from the oldxest Mac drive, the quaint singly-sided
400k model.  (The drive itself is totally incompatible with A2, and its
use on an A2 will blow the IWM drive controller chip!)  I used the short
beige cable, and it WORKED with my Apple II.

	At flea markets and elsewhere, I've collected about a dozen older
Mac drives --- the 400K tall drive and also the slim beige Mac 800K
external drive.  The 800K mechanisms is perfectly compatible with A2
Unidisk 3.5 drive and with the platinum 800K drive --- its mechanism can
be transplanted into those units, as I described in my II ALIVE article in
the winter 1997 issue.

	I am unable to get the Mac db-19 cables to run with Disk II.  Last
weekend, I tediously measured PINOUTS on the A2 db-19 cable vs. the older
Mac db-19 cables.  Here are the disturbing results:

	First, the A2 db-19 cable uses 18 lines, while the Mac db-19 cable
uses only 17 lines.  For A2, pins 5 and 9 are used, and pin 16 is vacant.
The Mac db-19 cable is vacant on pin #5.

	Is there any hope of modifying the Mac db-19 cable to make it work
with A2?  How vital is pin #9 wire line in the A2 drive cable?  I have
toyed with the idea that I could run a jumper in the A2 male plug from
pin 5 to pin 16, then on the IDE-20 change the crimp pin to position 5.
But this would do nothing about pin #9 ...

	Let me know!       Steve Buggie     buggie@unm.edu  


P.S.  I've been away from e-mail in the past month due to work pressures
buit will catch up with late hardware orders before the end of May; will
also respond promptly to e-mail through the summer.