6 Sep
2011
6 Sep
'11
12:44 p.m.
On 6 Sep 2011 at 19:12, Tony Duell wrote:
> The model II used full height 8 inch drives,
I'm pretty sure that
> they were AC powered (*motor*) the stepper was powered by 12 or 24
> vdc IIRC
Some later Model IIs, particularly in their Model 16 incarnation,
used half-height Tandon 848 drives. When they work, they're fine,
but there are a couple of design deficiencies that often kick up
problems. The drive uses 24V for the positioner and head-load,
but appears to use 12V for the spindle motor. The 12V is obtained
via a TO-220 7812 regulator that is inadequately heat-sinked.
Fortunately, there's a fuse as well as a 10 ohm resistor in series
with the 24V line, as the input capacitor to the regulator often
fails )probably from the regulator heat) as well. In any case, the
7812 tends to run very hot and some drives have shunt resistors
across the 7812..
Many 8" drives also need a -ve supply (-12V or
-5V, in the former case
it may well be regulated down to -5V on the drive PCB) for the
analogue seciton (read amplifier, etc). If that's mising you migth get
a drive that won't read, but that rail may well mot be essential for
any other part of the machine to work. Worth checking all supply
voltages at the drive.
The Model II was a late 1979 introduction; I'd be very surprised if
any 8" drives manufactured at that time required a -5V supply.
--Chuck