8" drive supply disparities (was Re: WTB: 8" floppy)

From: Richard Erlacher <edick_at_idcomm.com>
Date: Sat Jun 30 17:32:31 2001

Though I've heard of them, I've never seen an 8" drive that operated from the
Vcc supply alone, nor have I seen any printed allusion to them.

Back in the days when the 8" drive was in full usage, there were few drives
available that didn't use the three available supplies. In the years when
smaller drives were becoming popular, manufacturers of 8" drives figured out a
few things that might be impacting their reduced 8" drive sales. These included
the use of several supply voltage requirements, but that was partially dealt
with by using single-supply amplifiers, and the noise of the AC motors, which
was dealt with by using DC motors. However, the sheer mass of an 8" drive
mandated a cost that was easily beaten in the marketplace by the smaller drives,
and, no matter how well the 8" drives did with reduction of power supply demands
and in noise, once the smaller drives were able to produce the same capacity,
not to mention that the evolution of the hard drives of small form factors were
able to offset the capacity demand somewhat, the fate of the 8" drive was
sealed, even if its capacity could be doubled or tripled, since the combination
of floppy and hard disks was now a reality, and large capacity was no longer of
such large interest.

8" drives with which I've had contact, with a VERY few very old exceptions,
notably PerSci, have always used the Shugart-defined 6-pin connector with which
we all became familiar if we used 8" drives in the '70's. If the drive required
a supply, it was normally provided by the PSU that one commonly associated with
8" drive pacakges, e.g. the PowerOne CP206 and others of that ilk. If a drive
didn't need the Vee supply, it didn't matter that it was there. If it did need
that supply and your particular supply didn't provide the correct voltage, an
on-board regulator on the drive could be installed to handle that if it wasn't
already there. Moreover, many supplies were adjustable, either by tweaking a
pot or by changing a resistor (since they nearly all used the uA/LM 723
regulator, which worked in that way. If you simply hooked up a supply to a
drive without first verifying that the Vee supply was properly handled, one
might say you got what you deserved, however. Aside from the Vee issue, which
only occurred in a very few cases wherein there was no regulator on the drive
AND the supply was incorrectly set up, there was little likelihood of damage to
the drive or supply. The drive was unlikely to work if Vee was -12 volts,
however, if the drive was set up to use -5. Permanent damage to the drive was
unlikely however, since the devices involved were of a type normally used with a
bipolar 15-volt supply. While the biasing necessary to make these work at
bipolar 5 volts wouldn't work if the two supplies were unequal, serious or
permanent damage was unlikely.


----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Saturday, June 30, 2001 12:27 PM
Subject: Re: WTB: 8" floppy

> >
> > The connector definitions from the '70's, before they thought up the LSI
> > or even the intermediate board that actually didn't require the Vee supply,
> > however, relied on the presence of that negative bias for the read amp's.
> > you plug the DC supply compatible with the ORIGINAL version of that SA80x
> > connector into any drive that uses it, it will work, though the Vee and
> > the 24-volt supply as well, may be redundant.
> Almost....
> If the drive doesn't use the -ve supply (Vee) at all, then it doesn't
> matter if that pin on the power connector is connected to any reasonable
> -ve supply, unconnected, or whatever. It's simply not connected on the drive.
> If the drive _does_ use the -ve supply, then it can either be expecting a
> -5V stabilised supply or a -7V to -16V unregulated one, depending on the
> position of a link on the SA800 board). I would guess that some PSUs for 8"
> drives gave out -5V, others about -9V. Use the 'wrong' link setting and
> it'll either not work, or magic smoke might leak out. I have no idea what
> other manufacturer's drives did -- some of them might be -5V only, for
> example.
> Were there really 8" drives that were +5V only? (i.e. that didn't need
> the +24V line). I've never seen one.
> -tony
Received on Sat Jun 30 2001 - 17:32:31 BST

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