NOVA4 6070 disk -- whew!

From: Tom Jennings <tomj_at_wps.com>
Date: Fri Feb 4 02:25:03 2005

Success! But what an ordeal!

I removed the top head, got real zen with an 8X magnifier and the
desk halogen. Damned head was dirty; I did a crap job cleaning it.
I carved off a thin sliver of wood with which to clean and explore
the aero holes, leading edge, etc. Scrubbed off some carbony crud.
Got it spotlessly smooth and clean, washed it all out.
Re-installed and did static alignment.

(There's an electronic alignment procedure, similar to aligning 8"
floppy heads with an alignment disk, but (1) I don't have an
alignment disk and (2) pack interchangability isn't an issue and
(3) I don't have any existing packs to worry about so I'll just
re-format to this particular alignment.)

So I've got one cartridge left, the brand-new one still wrapped in
DG plastic. It's spotless. I mount it, spin up (with the servo
DISABLE/ENABLE switch set to DISABLE *), ... a horrible rumbling
noise! It's coming from the new pack, definitely something
spinning that is roughly dragging on something not. I demount, no
crap on the platter? Remount, check the plastic container's
alignment (the platter magnetically attaches to the spindle,
floating free, but close, to the enclosing plastic housing). Check
the housing all around, etc. Spin up -- NOISE!

Sigh, removable cart on the bench. Long story short, I hear a
rattle, and a broken screw head falls out... half the mag-latch
mechanism isn't attached, and falls down with gravity to drag on
the inside of the platter's mounting hub.

So that's why this brand-new, never-used DG 10MB removable
cartridge is sitting there in a plastic bag. It's broke. CRAP!

Well I had all the parts from the sacrificial cart that I turned
into the fixed platter. However it's of a different latch design,
so I had to transfer the removable platter into the old housing
and mechanism! HAIRY! The inner hub was filled with turned and
melted plastic, luckily the design of the hub fully contained the
shavings.

It worked. Well, heads load without crashing, a good start.
Electronics, if broken, I can fix.


POST MORTEM:

So what did I learn: One, I did a shit job of inspection. Though I
can't know, I have to assume the initial crash was my fault. I
underestimated the subtlety of the dirt. The dirt was very old,
and very hard. Plus, my eyes are 50 years old now, not 21; I was
actually surprised how much more was revealed with the magnifier.
Two, I didn't *fully* learn the lesson of the first crash when I
finally did remove the heads for a 'proper' cleaning after the
second.

So I rethought my general approach (non-heirloom: assess condition
(overall: excellent) therefore fix only things needing fixing) and
still think it is correct for this machine, but I neglected to
consider that that disk-drive heads/platters is simply a unique
situation. Heads and platters are simply to precious, and
problems manifest too disastrously. A counter example is the tape
drive(s); while I'll be paying a bit more attention (ahem) the
relationships 'tween head and media is vastly simpler, easier to
grok and to fix. And I'm testing with a tape marked "bad" :-)

tomj




(*) The drive sequences airpump on, spinup, brush cycle, head
load. I disabled the servo so I could let the air pump run extra
time, and manually trigger 3 - 4 extra brush cycles, and generally
flush things out.
Received on Fri Feb 04 2005 - 02:25:03 GMT