Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cunixf.cc.columbia.edu!ezk
From: ezk@cunixf.cc.columbia.edu (Erez "HWank1" Zadok)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Making a floppy drive ignore high density hole
Keywords: 3.5 drive, HD, DD, switch
Message-ID: <1990Jul21.083532.15802@cunixf.cc.columbia.edu>
Date: 21 Jul 90 08:35:32 GMT
References: <11547@ingr.com> <1990Jul19.021714.10040@world.std.com> <803@digi.lonestar.org> <1990Jul19.193954.29829@cunixf.cc.columbia.edu> <25160@nigel.udel.EDU>
Reply-To: ezk@cunixf.cc.columbia.edu (Erez "HWank1" Zadok)
Organization: Columbia University Center for Computing Activities
Lines: 44

In article <25160@nigel.udel.EDU> ih@udel.edu (Charlie Ih) writes:
> In article <1990Jul19.193954.29829@cunixf.cc.columbia.edu> ezk@cunixe.cc.columbia.edu (Erez "HWank1" Zadok) writes:
> >In article <803@digi.lonestar.org> mfrohman@digi.lonestar.org (Matthew Frohman) writes:
[...]
> and thanks.  Just curious, why could you just leave the switch there
> (in open position) and connect the "external" switch in parallel with it?
> This would require less work but more important have less chance to damage
> the circuit board.  Since I don't know the actual situation, maybe
> the removal of the switch was necessary.  Thanks again!
> 
> Charles S. Ih

I gather from your question that you're not familiar with basic electronics.
That's ok.  Here's an explanation I hope would make sense.

First, if you've had some experience with soldering, you'd know that the
faster you solder out the switch the better it is.  I've had my share of
heat-until-the-contacts-pop-off-the-board experience (you EE people *know*
what I'm talking about.)  Other than that, I see no possible harm to the
circuit board.

I could not have left the internal switch in open position b/c the minute I
put a DD floppy inside (no 2nd hole) the internal switch would be pushed
down, thus creating a short between the two points.  Now, if I also have an
external switch outside, which I wanted to set to the "open" position (force
a break of the connection), then the internal switch being connected in
parallel would override the external one and the overall result would be
that I would not be able to format a DD as HD.  (Resistors in parallel.)

The setup I chose is *real* simple.  I didn't want any software solutions
that might require me to use up any of my precious RAM (extra driver or
command loaded into CONFIG.SYS).  I didn't want to create any more
complicated circuitry inside my 3.5 drive, like a 3th "auto-sense" switch
(not that it couldn't be done.)  Simplicity usually works the best (ask LISP
programmers! :-)

Occasionally I try to read the wrong size floppy in the wrong switch
settings.  No big deal.  I get the usual dos barf "abort, ignore, retry,
etc", flip the switch, and hit 'R'.  Works like a charm.

Erez.
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