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From: jeffj@synsys.UUCP (Jeff Jonas)
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: <408@synsys.UUCP>
Date: 24 Jul 90 06:23:13 GMT
References: <11547@ingr.com> <1990Jul19.021714.10040@world.std.com> <803@digi.lonestar.org>
Reply-To: jeffj@synsys.UUCP (Jeff Jonas)
Organization: Jeff's House of Electronic Parts
Lines: 32

I like the hardware solutions, but these are less intrusive
and require less skill and tools.

I have 2 ways to trick my drive to writing disks with the
write protect hole
(the same trick can be used for low/high density).

1) put a piece of tape or "post-it" on the BOTTOM of the hole.
This will (de)press the switch when the floppy is inserted.
Be sure not to interfere with the hub!

2) I opened the floppy drive and taped down the switch.
This is less dangerous to the drive than desoldering/jumpering.
I'm not going to mess with boards with surface mounted parts,
especially when it's my money!

All the 3.5" floppy drive mechanisms I've seen require the disk to
move down to engage, so the hole detectors are tiny button switches,
not the optocouple used for 5.25" drives.
This is similar to the write protect holes used in cartridge tapes,
audio cassettes, and videotapes.
They're sensed by a pin/lever to a switch.
This means that the hole needs to be covered, but not light proof.
Ordinary cellophane ("Scotch") tape will suffice, but that tends to
leave the envelope sticky.

By the way, the 3.5" floppy drives used in the PS/2 don't have
a switch to detect density.  The mechanism is half height, but
in a full height casing to fill the full height cabinet bay.

Jeffrey Jonas
jeffj@synsys.uucp