Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!ucla-cs!dkim
From: dkim@maui.cs.ucla.edu (Dong Hun Kim)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 3.5" 1.44/720K drive question
Summary: HW modification 3.5" 1.44/720
Keywords: 3.5" drive, 1.44M, 720K
Message-ID: <22063@shemp.CS.UCLA.EDU>
Date: 21 Mar 89 20:17:43 GMT
References: <8168@xanth.cs.odu.edu>
Sender: news@CS.UCLA.EDU
Reply-To: dkim@cs.ucla.edu (Dong Hun Kim)
Organization: UCLA Computer Science Department
Lines: 55

In article <8168@xanth.cs.odu.edu> rlb@cs.odu.edu (Robert Lee Bailey) writes:
>which detects the presence or absence of  a hole to determine whether
>the media is 1.44M or 720K. 

There is a small (tiny) pin which probes the hole. The pin is located
at the lower right hand side inside the drive ( just below the hole ).
If the pin is pressed (no hole) it recognizes the diskette as 720K,
otherwise 1.44Mb. 

> Has anyone successfully modified their
>hardware and/or software to defeat this feature?  (I use the term
>"FEATURE" with tongue in cheek!)  I want to use cheap 3.5" diskettes
>at 1.44M, but, this asinine gimmick forces us to format to 720K.
>

The pin is essentially a small switch, so you can bypass
this switch by installing another small switch outside the drive.
You can buy such a switch at any Radio Shack store.
How to install the switch :
   - solder a pair of wires to the metal part at the base
     of the pin case; one wire at each side.
     one connects to (a) and one connects to (b)
     (see diagram below)
   - solder the wires to the switch you bought
   - drill the front bezel of the drive to install the switch,
     to make it accessible from outside. Tighten the switch screws.
   - Now, switch ON means high density (1.44), 
                 OFF means normal operation : if hole exist -> 1.44Mb
                                              if no hole    -> 720Kb

                         |
                         |  pin
                         |
                   a === | ==== b   metal on the base
                         |
                       =====
                        sp
                        ri
                        ng

                       -----
                       
I implemented the above modification with very satisfactory
results on Toshiba, Teac, and Sony drives.
However, Sony drives are different from Toshiba and Teac.
In Sony, if the two metals in the base in contact, it recognizes
the diskette as 720K (the opposite of Teac and Toshiba).
So, you must remove the pin and spring, etc.
Now, ON -> 720K
    OFF -> 1.44M

I hope that helps.

Dong Kim
dkim@ucla.cs.edu