30 May
2019
30 May
'19
12:20 p.m.
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?
Thanks
Andrea
30 May
30 May
8:56 p.m.
On Thu, May 30, 2019 at 8:20 PM shadoooo via cctech
<cctech at classiccmp.org> 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
good.
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).
-tony
31 May
31 May
8:09 a.m.
On 05/30/2019 02:20 PM, shadoooo via cctalk 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?
I don't think this is a field procedure. Definitely, way
back around 1980 or so, they had some bum adhesive that held
the internal filter in the RA80 and RA82 HDAs, as I recall,
and they had to replace all HDAs in the field, over time.
They had some scheme where the oldest HDAs were replaced
first, as the adhesive degraded over time, so they knew they
had a couple years since new before the problem would
occur. It was a BIG expense for DEC.
Presumably, all of these HDAs (that were under maintenance
contract) that had the bad adhesive in them were replaced
years ago. 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.
I think the procedure to update those HDAs was a pretty
involved disassembly.
Jon
8:12 a.m.
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.
Jon
8:46 a.m.
On Fri, May 31, 2019 at 4:12 PM Jon Elson <elson at pico-systems.com> wrote:
On 05/30/2019 10:56 PM, Tony Duell via cctalk wrote:
Sure, if you _need_ them close to the heads (as you probably do
with the smaller amplitude, higher frequency signals in modern
drives).
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.
-tony
[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.
Jon
8:41 p.m.
On Fri, May 31, 2019 at 11:17 PM Jon Elson via cctalk
<cctalk at classiccmp.org> 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.
-tony
Jon
1806
days inactive
1808
days old
5 comments
3 participants
participants (3)
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