Unexpected floppy behavior...

[Dwight K. Elvey]

>From: "Bill Sudbrink" <wh.sudbrink at verizon.net>
>
>Well, unexpected by me anyway.  I've built a data sep circuit
>from that schematic I asked for advice on earlier.  Works like
>a champ.  I tied the circuit into a piece of ribbon cable so
>that I could pretty much attach any drive I wanted to try with
>it plus still be able to keep my OSI more-or-less unmodified
>and use the original drive.  The drives I am using are a pair
>of Toshiba FDD 5451s.  After testing each drive individually,
>I attached another IDC card edge connector to my setup and
>tried again.  Nothing worked!  Not only did it not work, it
>trashed the diskette I was testing with.  Went back to one
>at a time and everything worked again.  After a good bit of
>trying to figure out what was wrong, I discovered that the
>+5 volt pin in the power connector I was using for the #2 (B)
>drive had pushed out of the nylon plug so that the drive was
>unpowered.  Having either of the drives unpowered on the cable
>caused the other drive to screw up.  The two drives cooperate
>just fine when both have power.  I don't remember ever seeing
>this kind of problem before... I seem to remember having unpowered
>drives hanging off of cables with no ill effects.  I guess that
>some of the signals (write gate for instance) must be getting
>pulled low by the unpowered unit.  Is this normal floppy
>behavior and I'm just remembering wrong?
>
>Thanks,
>Bill
>

Hi Bill
 Remember, things are active low. If the terminator was
unpowered, it will pull the write gate to active ( trashing
the disk ). If the drive that is unpowered is not the one
with the terminator, it may not have been able to pull
the lines high enough. Still, an unpowered drive should
load the lines some. This is not a good thing.
Dwight