Floppy disks mount duplicated on Mac 512K

[mitchW]

I am having an issue with my recently restored 512K. That 512K was upgraded (RAM, SCSI, Mac Plus ROMs, etc.) - so it is essentially a Mac Plus., but I am not sure if upgrades are the culprit.

Original 800K drive was beyond repair (bent heads), so I managed to find and repair a 1.44MB drive (MFD-71W), that should work in this Mac.
That drive works, ejects disks, formats disks, etc. But no matter what System software I boot (I used 1.1 and 5.5), I get duplicate mounted disks on desktop. So I get two System Software disks mounted on desktop, despite I only inserted one floppy. If I eject one disk, it will eject it, but the other will stay mounted.

When I checked the info, it sees one disk as it is in internal drive, and other in external. Of course I only have internal floppy drive hooked up!
Even if I boot to MacPaint 400K disk, it does the same thing, or if I boot off the HD20SC, it is also the same.
Did anyone have a similar problem? I would like to get it solved.

 

[jmacz]

If I remember correctly there are two enable signals, one for internal and one for external, both from the IWM. Curious if they might be shorted causing the internal to respond as both external and internal. Or maybe something’s wrong along these lines with the IWM. I think there is a shared filter pack between the IWM and the two floppy ports (internal ribbon connector and external port) that could perhaps be shorted as well.

BTW, you said the 1.44 floppy should work.. it certainly won’t work as a 1.44mb floppy since the 512k and Plus (and most SEs) had the IWM instead of the SWIM chip.