2 Mar
2002
2 Mar
'02
1:27 p.m.
On Sat, 2 Mar 2002, Tony Duell wrote:
If tghey are Diablo 31s....
The spindle motor has a funny speed control where about 90% of the
voltage needed to run at full speed is appled through a power resistor. A
digital circuit decides if the speed is to low and shorts out the resistor. I
think they got 1% speed control with that simple circuit - of course the
spindle has a lot of inertia...
Other funny thing is I think the power supply for the drive is the
same as a Hytype I power supply. The Hytypes use the same encoder as the
drives head positioner... (as did the Singer model 40 disk drive where the
Diablo design presumable came from)
> For nostalgic reasons, I have wanted to
acquire two particular disk drives
> for a PDP-11 of mine... I don't remember what they are called or what brand.
> But - there are two of them in the very far right of the symbolics rescue
> picture at the top of the rack with light brown trim line across the front.
> Can anyone tell me what those are - and if there are any around to be
> obtained? How hard are they to work on? Is the positioner based on patterns
> on the drive or a glass reticule?
The positioner does not depend on any servo patterns on the disk surface
(so it's like an RK05 -- in fact it uses the same media). The position
reference is a 'transformer' made from PCB tracks mounted on top of the
positioner mechanism. One PCB contains the 'primary' and it rotates
relative to the other which contains a pair of 'secondaries. The output
signals are pretty similar to those from the optical transducer in the
RK05, actually.
The positioner itself is a permanent magnet DC motor (!) -- with carbon
brushes. I have no idea how they got it to work, but it does work. The
spindle motor is another permanent magnet DC motor, directly driving the
disk spindle.
The electronics is half a dozen plug-in cards in a backplane which can be
pulled up for access. It's not hard to work on, and the components are
all standard IIRC. I have (somewhere) the service manual. The PSU is
external (+/- 15V IIRC).
Peter Wallace
IIRC they're RK03's aka Diablo type 31?
You must have an RK11-C controller...
Or make a drive select line decoder (a couple of chips IIRC) for the
RK11-D. Those actaully existed commercially in the UK -- Plessey sold
them to use Diablo drives (and similar units) with the RK11-D or their
clone of same.
-tony