Re: DuoDisk 5.25 bug (ctrl-oa-reset)

[spector@vax2.concordia.ca (Mitchell Spector)]

In article (Chris Deschu) writes...
>
[snip]
>Hmm, I'll have to check mine out.

        Authorized Apple dealers are/were supposed to do the modification
fix free, though it seems simple enough for virtually anyone to perform (if
you can use a screwdriver, you should be able to do the fix yourself). From
what I read, there's no soldering involved -- you just cut or break off two
small capacitors. I'll post the detailed information for doing the fix
below (Thanks to Dave V. for sending it to my mailbox! :-)

>Interesting. I have a DuoDisk on my ROM 1, and it has worked
>flawlessly from the day I plugged it in. I haven't checked the
>board number yet, though. Another one of my friends also uses
>a duodisk on another ROM 1, and again, no problems. Anyone use
>one on a ROM 3 yet? I wouldn't expect any difference.

	I've never tried hooking up my DuoDisk drives to either my
ROM 01(s) or ROM 3 (bearly see a need for even my platinum 5.25), but
it *will* function without the modification. The problem has to do with
certain configurations, like having the DuoDisk last on the GS smartport
chain. (This involves a separate fix from the one above -- simular though)

================DUODISK 5.25 FIXES (begin)============================

This evening, I received with great appreciation, the Duodisk mod I had been
asking for. They were courtesy of John Daniels (ah499@cleveland.freenet.edu).
He asked me to post it here so that others could benefit as well. Here goes!
+---------------------------------------------------------+

Subj: Duodisk Modifications

There are TWO modifications that should be made to Duodisk drives.

The first one was recommended by Apple perhaps 5-6 years ago, to solve
occasional problems with trashing diskettes by Duodisks.  The solution is to
remove 2 capacitors.

The 2nd modification is only required for Duodisks to be used on Apple IIGS's
(though the modified Duodisk will still work fine on older Apple II's).  It
requires removing a resistor.  The problem is that the Duodisk draws just a
little too much current. This problem is especially apparent when several
drives are daisy-chained from the GS Smartport. Problems are MOST likely to
occur when the Duodisk is daisy-chained from a Unidisk 3.5 Drive.

DUODISK MODIFICATION - REMOVAL OF CAPACITORS

OK, here's the first modification for the Duodisk drive.  This mod should be
done on ALL Duodisks, no matter whether they're used on //e's, IIGS's, etc.
The problem was that diskettes would sometimes be damaged when doing an
Open-Apple-CTL-Reset, or when using disks with certain kinds of copy
protection.  The mod was in an Apple dealer service bulletin several years
ago.

Here's an excerpt from the bulletin, describing the problem:

  "Data on disk is damaged when using "Open-Apple-CTL-Reset" for rebooting,
  or when using software with certain copyright protection schemes.
  Analog board PN is 676-[]101 or 676-[]102."

The Analog board is the one inside Drive 1 in the Duodisk.  You may have to
unplug the cable near the back right of the board to see the board's model
number.  Anyway, if you have the -101 or -102 board, just break off or cut
out Capacitors C29 and C30 (at board locations A1 and B1, respectively).

I've done this on all 3 of my Duodisk drives, so I can vouch for the safety
of the procedure.

DUODISK MODIFICATION - RESISTOR REMOVAL

Here's the second modification for your Duodisk drive.  This is the exact
message as posted on Compuserve in 11/86 by an Apple Computer employee:

**********************************************************************

Duodisk Mod                13-Nov-86 1150               Accesses: 12

    This file describes how to modify your duodisk for safe use on the GS.
    Obviously, it is preferable that you have it done by the dealer, but if
    you want to do it yourself here's the info... Questions/problems to
    76703,3030, PM

Using the DuoDisk with the Apple IIGS

The DuoDisk can not be used as the last daisy chained device on the
built-in IWM disk port of the Apple IIGS. For instance, a UniDisk 3.5
will be rendered inoperable when the DuoDisk is installed in the above
manner - although using the DuoDisk by itself is not a problem.

A qualified technician will have to modify the DuoDisk analog
board if the DuoDisk is to be used as the last device on the
chain. Please use the following procedure to determine how to
modify the analog board.

IDENTIFYING WHICH ANALOG BOARD YOU HAVE

Remove the top cover as documented in Technical Procedures. Turn
the drive so that thidentifying number will be at the bottom left of the analog
board. The number might read 676-[]101, 676-[]102 or 676-[]107.

PERFORMING THE MODIFICATION

If the I.D.# for the analog board is 676-[]101 or  676-[]102, use
a pair of nippers and cut out resistor R8 (located at position A2).

If the I.D.# for the analog board is 676-[]107, use a pair of
nippers and cut out resistor R39 (located at position A1).

***************************************************

============================== end =============================

BTW -- Can someone verify if capacitors C29 and C30 are small brown,
oval-shaped, directly in line with each other (going downards) and
each next to the 4-pin black plus connectors on the analog board?
Just want to be sure I clip the right ones... 

>___________________________________________________________________________
> |___              Chris Deschu                       cdeschu@nyx.cs.du.edu
>_|_|con   (610)791-3596   4804 Bowood Street, Center Valley, PA. 18034-9628
>:-)|echnologies is IT in the Lehigh Valley for Apple ][ Consulting & Repair

Mitchell Spector
sb_spec@pavo.concordia.ca / spector@vax2.concordia.ca