DEC R80 HDA details

Tony Duell ard.p850ug1 at
Thu May 30 22:56:00 CDT 2019

On Thu, May 30, 2019 at 8:20 PM shadoooo via cctech
<cctech at> wrote:
> Hello,
> I'm in the process of cleaning and hopefully restore to operation of a DEC
> R80.
> The unit has some minor sign of corrosion, however it's VERY dirty, even
> inside the hood.
> The filters are obviously to be removed and replaced, as they are
> disintegrating.
> Also foam parts between the boards must be replaced.
> Aside from obvious parts, there's something that should be replaced /
> cleaned inside the HDA (foams, filters or rubbers), which could damage the
> disk permanently in case it's turned on after decades if not "cured" before?
> Anybody has some good pictures of the HDA inside, after cover removal?

The HDA was never intended to be dismantled in the field, and I think that
dismanrling it outside a clean room would probably do a lot more harm than

I read somewhere that these HDAs were assembled in a rather odd way.
The spindle and platters was placed in the bearing in the lower half
of the casing, then the top casing fitted and bolted down. Then the
positioned/heads was inserted from the front and fixed with screws on
the top and bottom. The cables were then plugged into the preamplifier
PCB [1], the front cover fitted and held on with the clips round the edge.

[1] I feel DEC got one thing wrong here. The preamplifier ICs are inside
the HDA and thus can't be replaced. On some other drives (Micropolis,
for example) the ICs are in sockets on the outside face of the PCB so
you can flick them out and replace them without needing a clean room.

What I have never managed to find out is how they slid the heads over
the platters without scraping the surfaces. Was there a special spreader
'comb' tool? There's not much space to insert one.

It's worth looking at the printsets for the RA80, RA81 and RA82 as well. The
HDAs are different in the different models of drive but are mechnically very
similar. One of the printsets has rather more information than the others (I
forget which).


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