The connector definitions from the '70's, before they thought up the LSI board
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. If
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 possibly
the 24-volt supply as well, may be redundant.
It's quite true that supplies concocted with the intention of eliminating the
redundant supplies won't work with the older drives. However, it's unlikely
they'll hurt the drives, though the drives won't work properly.
Dick
----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Friday, June 29, 2001 3:20 PM
Subject: Re: WTB: 8" floppy
> >
> > I'm not sure I go along with that.
> >
> > While it's advisable to check requirements before hooking up any device,
I've
> > got to say I've never seen an 8" drive that used the "conventional" DC
supply
> > connector for 8" drives, as defined by the Shugart folks, et al back in the
> > '70's, that wouldn't work on precisely the same power configuration, using
+24,
> > +5, and -5 with the associated returns. While there were some drives that
would
> > tolerate -12 in place of the -5 if you jumpered them approproately, I've not
> > seen any that would be damaged if you overlooked that detail and simply
hooked
> > up -5. Moreover, the majority of drives available by the mid-80's,
admittedly
>
> I have just dug out the service manuals for the SA800 and SA850 drives.
>
> According to the SA800 manual, the DC power connector pinout is :
>
> 1 +24V DC (+/- 1.2V) (1.7A max)
> 2 Ground (+24V return)
> 3 Ground (-5V return)
> 4 Either -5V (+/-0.25V) or -7 to -16V (jumper option) (0.1A max)
> 5 +5V (+/- 0.25V) (1A max)
> 6 Ground (+5V return)
>
> Later drives, using the LSI PCBs (which a 40 pin chip on it), do not use
> the -ve supply. Pin 4 is simply not connected.
>
> According to the SA850 manual, the pinout of its DC power connector is :
> 1 +24V (+/-2.4V) (1A max)
> 2 Ground (+24V return)
> 3 Ground (not shown in table of connections, shown on schematic)
> 4 Not Connected
> 5 +5V (+/-0.25V) (1.1A max)
> 6 Ground (+5V return).
>
> So it is possible to have a PSU that will work with the SA850, but not
> with older (and in my experience more common) SA800s. The latter need a
> -ve supply, the former do not. There is no danger in connecting a -ve
> supply to pin 4 on an SA850, though -- that pin is simply not connected
> on the SA850. So you can plug the SA850 into the PSU for an SA800.
>
> Now, the drives that use a -ve supply rail have an on-board 79M05 that
> regulates the -7 to -16V down to -5V. That regulator can be bypassed by a
> jumper to select -5V input.
>
> The -5V line is used by the write driver (discrete transistors, probably
> wouldn't mind -16V for a short time), and the read amplifier (592 video
> amp, 8T20 monotstable, probably wouldn't like -12V or -16V). I certainly
> wouldn't want to try it!
>
> > late in the 8" drive's market life, didn't even require the negative
voltage.
> > Oddly enough, even the later 8" DC-powered drives from Shugart, Tandon, and
> > others, used that same connector for their DC supplies, though several of
them
> > immediately regulated the +24 down to +12. NEC's DC-powered FD1165's, by
the
>
> Presumably to maintain compatability so you could plug the newer drives
> in place of the old ones...
>
> > way, were a noteable exception in that they used the same little connector
for
> > power as the 3-1/2" drives use. That was why I gave away the ones that came
> > into my possession. I don't know what their DC power requirements were.
>
> One 'nasty' relates to the Archive Sidewinder, a QIC tape cartridge
> drive. This thing has a 4 pin power connector identical to the ones on
> 5.25" floppy drives, etc). Ground on the middle 2 pins, +5V where you'd
> expect it, too. But the other outside pin is +24V, not +12V. I am told
> that some Suns used this drive and had a special power cable for it
> carrying the right voltages. Get then mixed up when assembling the
> machine, and you might plug +24V into a hard disk expecting +12V. The
> results, apparently, are not pleasant.
>
> -tony
>
>
Received on Fri Jun 29 2001 - 21:19:58 BST