Stripping an RA80

Tony Duell ard.p850ug1 at
Sun Jan 8 13:02:26 CST 2017

On Sun, Jan 8, 2017 at 6:46 PM, Robert Armstrong <bob at> wrote:
>>Tony Duell <ard.p850ug1 at> wrote:
>>R80 the lines are outputs from the drive giving the coding of the ready lamp cap
> I was always thought that the R80 had to be unit #0 to function, but I admit that I've never tried
> anything else.  I wonder if that's not true??  The RL02 drive(s) on the IDC can be any of units
> 1, 2 or 3.

I don't know about the 11/730's IDC. I was just looking at the R80
schematics, the unit number
lines are output on the 60 wire cable. Maybe the RM80's massbus box
uses them or something?

A quick look at the printset and technical manual suggests that the
11/730 IDC compares the
drive select number from the appropriate output register with the unit
number from the R80 (set
by the ready lamp cap). If they match it uses the R80 logic, if not
then it uses the RL02 logic.
I have no idea if the nomal software will work if the R80 s anything
but unit 0, but it looks like
the hardware was designed to allow for it.

>>The HDA is the only major unit I can't repair (yet!).
>   Yeah, same here.  In addition to the 11/730 with one (dead) R80, one RA81 and one RA82,
>  I have a MicroVAX-III with an RA82 drive.  Keeping them all working has been a real challenge.

The only (other) SDI drive I have is an RA60, and I have no packs for
it. I doubt I will ever use it.

> Fixing the electronics and mechanical parts isn't too bad, and I have plenty of spares, but the

Apart from the ROMs (and those 8355s/8755s are not suported by most
programmers/readers now
available), there are no custom parts on the PCBs that I've spotted.
There are custom chips on
the PCB on the front of the HDA and unlike one Micropolis drive I work
on, you can't replace them
without dismantling the HDA (in a clean room). There are also plug and
socket connectors on that
PCB -- inside the HDA. I hope those don't suffer from bad contacts!

> HDAs don’t seem to be very reliable.  I get the impression that they were designed with a finite
> number of spin up/spin down cycles in mind, and once you exceed that limit they die.  Fortunately

Quite likely. Which means we are less kind to them than we should be
in that we don't keep them
running (or at least I won't)

> I've been able to find spares for the RA81 and RA82 HDAs, but R?80s seem to be pretty rare.


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