DEC R80 HDA details

Tony Duell ard.p850ug1 at
Fri May 31 22:41:44 CDT 2019

On Fri, May 31, 2019 at 11:17 PM Jon Elson via cctalk
<cctalk at> wrote:

>  As far as I remember, there IS no removable
> cover on those HDAs, they were hermetically sealed except
> for a tiny, filtered, pressure relief vent.

Well, the HDA was assembled, so it can come apart again. The
RA82 printset gives rather more details of the HDA than the others,
(different HDA of course but the same idea). But I think that opening
it up outside a cleanroom will do a lot more harm than good.

> I think the procedure to update those HDAs was a pretty
> involved disassembly.

Actually, getting the whole HDA out of the drive is quite easy. It's
even in the user manual, as it is sugested that you remove the HDA
to reduce the weight of the drive if you want to rack-mount it. Basically :

Raise the logic chassis on the gas struts

Lock the heads with the lever on top of the HDA. The drive should really be
running for this to avoid scraping the heads across the disks. Then power
down (obviously!)

Lift the drive belt off the HDA pulley using the lever on the right hand side
of the drive chassis.

Unplug the cables: Two small ones on the front of the HDA (servo head output
and positioner drive) and the largest one (rear edge) of the read.write PCB
on top of the HDA.

You can remove the read.write board now, or take the HDA out with it attached.
To remove it, unplug the other 2 cables and take out the 4 fixing screws

Remove the 4 fixing nuts/washers for the HDA

Lift it up and out. You can stand it on the 'feet' moulded into the front
cover of the HDA.


> Jon

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