UniDisk 3.5 to Apple 3.5 conversion (Hacker's Corner)

[pubpc1@library.ucla.edu]

(In response to the recent questions asking how to make a
UniDisk 3.5 work like the Apple 3.5 drive...This also answers
Randy Shackleford's comment of the Finder polling all drives
- Apple 3.5 drives are polled SILENTLY while UniDisk 3.5 drives
must have their drive motors intermittently activated.)



Upgrading your 3.5" drive: UniDisk 3.5 to Apple 3.5 modification


You've upgraded from an Apple IIe with a UniDisk 3.5 controller to
a GS and now you have a problem.  When the UniDisk 3.5 is connected
to a GS, it is dog slow.  You have to set the interleave to 4:1 to
make it run at a somewhat respectable pace when loading those large
GS programs and data files, but this causes speed penalties when you
take it to a friend's GS with an Apple 3.5 drive.  Even worse, the
drive is AUDIBLY AND VISIBLY POLLED by the Finder.  It sounds
terrible.  Now the Finder polls every drive, true.  But on the
Apple 3.5 drive, this polling does NOT start and stop the drive
motor.  An Apple 3.5 drive is silent, but aware in a program such
as the Finder.  You wish you could magically transform your slowpoke,
noisy UniDisk 3.5 into an Apple 3.5 (besides, this would make it
usable as a convenient external drive on your Mac sometimes...).

If your UniDisk 3.5 was manufactured in mid-1988 or later, you are
in luck.  The later UniDisk 3.5 models can be (fully reversibly)
modified to work like an Apple 3.5" drive.  Make sure the power is
off and the drive is disconnected from the computer.  Get out your
screwdriver set and get ready to roll!

First, remove the screws from the UniDisk 3.5's case and remove the
ABS plastic shell to expose the internal guts of the drive.  Check
the label on the mechanism: if it is a Sony model beginning with
"#51W-" followed by two or three characters, your drive can be
upgraded.  If the mechanism is different, you are out of luck.  :(

Now that you have the UniDisk 3.5 opened and verified that the unit
has the right model mechanism, take a look at how the internal
components of the drive are put together.  There are two circuit
boards and the drive mechanism.  The interface cable is connected
to the lower circuit board and there is a ribbon cable that connects
the top and bottom circuit boards together.

First, unplug the interface cable from the lower circuit board.
Next, unplug the ribbon cable (that connects the two circuit boards)
from the top board.  Finally, plug the interface cable into the
top circuit board.  When you are finished, the interface cable
that was originally connected to the bottom circuit board should
now be connected to the top one and there should be one cable
dangling.

Close the case by reassembling it with the screws and connect the
drive to the computer.  Now you can boot into the Finder and
remove the UniDisk 3.5 driver from the *:System:Drivers folder
and use the Apple3.5 driver instead.  Make sure to recopy all your
4:1 interleave disks to 2:1 interleave for fastest access.
This modification is also useful for Macintosh, IIc Plus, and
Apple IIe with SuperDrive controller users.

If you are still suffering the rattling noise and slow access of
a UniDisk 3.5, why not give this modification a try?  It is
completely reversible should you ever need to use the drive on a
IIc or a IIe with a UniDisk 3.5 controller again.

-Scott G.