DEC R80 HDA details

Tony Duell ard.p850ug1 at
Fri May 31 10:46:43 CDT 2019

On Fri, May 31, 2019 at 4:12 PM Jon Elson <elson at> wrote:
> On 05/30/2019 10:56 PM, Tony Duell via cctalk wrote:
> > [1] I feel DEC got one thing wrong here. The preamplifier
> > ICs are inside the HDA and thus can't be replaced.
> This was pretty common practice in a number of drives from
> that period.  Now, it is common for the read amps to be on
> the individual hear arms, to get them closer to the heads.

Sure, if you _need_ them close to the heads (as you probably do
with the smaller amplitude, higher frequency signals in modern

But in the R80, the preamplifier ICs are on the PCB that is fixed to
the inside of the front cover (the transparent plastic part) of the HDA.
The heads and positioner coil are plugged into connectors on the
inside face of the PCB, the cables for the positioner drive, servo
head output and r/w PCB areo n the outside face. The ICs are also
on the inside face meaning they can't be field-replaced (although a
schematic of this PCB is in the printset).

The Micropolis 1200 series (8" winchester drives) have a similar idea
with the PCB mounted on the HDA But here the ICs are in sockets on
the outside, meaning they can be replaced without letting any dust, etc
into the HDA.


> Jon

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