Data General 6070 disk system start up

updated 9 mar 2020

Tom Jennings, 10 February 2005

I'm bringing up this machine as fast as reasonably possible -- or unreasonably, in the instance of the 6070 disk system.

I really screwed up, but recovered from my folly. I underestimated the difficulty of cleaning the heads -- it took actual physical force to get the crud off. At the same time it's sensitive to cleanliness, and I don't know about you, but I don't have a clean-room here. You can read about (and learn from) my stupid mistakes.

From [email protected] Wed Jan 26 11:33:36 2005
Date: Wed, 26 Jan 2005 11:33:35 -0800 (PST)
From: Tom Jennings 
To: "General Discussion: On-Topic and Off-Topic Posts" 
Cc: "General Discussion: On-Topic Posts Only" 
Subject: Data General NOVA4 status

Well things are moving along very nicely, I'm going to power up in
the next few days. I've been picking on it each night (30 min - 2
hrs) and it's pretty much ready to begin power-up.

I took another look at the DG LP2 that "faulted". With a dry
paintbrush and vacuum cleaned out the dustbunnies and a few
spiders, esp. attention to the photo-interruptor. Loaded paper
into it, powered up. This time carriage zeroing worked, everything
behaved including self-test printing out the charset onto
greenbar.  The "new" ribbons seem dried out and the print is
yellow-gray (likely from Bakersfield heat) but I'll try another or
WD40 the ink ribbon. Washed it all down, other than a couple of
scuffs it looks like new.

Completed all the rack wiring, made a terminal (console) cable up
from the stub that got cut off for transport. Fan filter, rack
panel fillers all in.

Took a look at the other chassis; one now empty (DG salesmammals
talked customer into too many (profitable) racks, as Bruce
suspected :-) one's got the big analog mux thing (more, next
message), the remaining has the second tape drive (6023) and the
4300 expansion chassis.  Which I might keep -- ask me in a month
-- it contains a 16 in/16 out digital interface and I think a
one-channel A/D and D/A. Nice.  Big though, we're talking 14" rack
space but it's mostly air (lots of slots).

Laid out all the docs, culled more dupes, which Bruce will get (hi
Bruce :-) Bought binders on the way into work today for never-used

My lab, quickly outfit last fall (moved out of my nice,
purpose-built lab, which we turned into a rent-generating
apartment -- when I get sad, I think of the income :-) has crappy
power. I'm not sure it's got enough amps to run the CPU, tape and
disk.  Umm, we'll see, the obvious way.

From [email protected] Mon Jan 31 12:03:39 2005
Date: Mon, 31 Jan 2005 12:03:39 -0800 (PST)
From: Tom Jennings 
To: "General Discussion: On-Topic and Off-Topic Posts" 
Subject: DG NOVA4/X runs

Well I just put a cord on it, plugged it in and powered on. No
smoke escaped.

The CPU passes self-test (no idea what it really checks, but it
alleges to be thorough) after I seated the memory board (I forgot
just how tough to seat the 15 in square DG boards are).

I can poke memory, registers, etc just fine. Took a bit to get the
console wired right (to minicom on a laptop, 9600/8/n/1) as the
sample cable (from the orig. install) was misleading.

The tape drive probably has a bad vacuum sensor; I'll look at it
Tuesday again. Might be cable fell off. It otherwise loads the
tape and one vac col does the right thing. Other functions seem to
work. I have a 2nd tape drive, not yet tested.

The disk (10 fixed, 10 removable) is not behaving right. Problem
with load/ready. Looks mechanically OK but I will do one more test
before the covers come off and the scope and DVM come out.

Tom Jennings 

From [email protected] Wed Feb  2 10:36:44 2005
Date: Wed, 2 Feb 2005 10:36:43 -0800 (PST)
From: Tom Jennings 
To: "General Discussion: On-Topic Posts Only" 
Subject: NOVA4 6070 disk booboo

Decided to try to get the Data General 6070 disk (10 fixed 10 removable)
going last night. There's reasonably complex LOAD/READY logic,
but from the indicators it wouldn't go ito either state.

Got out the schematics and docs, found a nice startup flow chart
and checked each signal. (DG does a great job on docs; there was a
flowchart and table of signals, each with a drawing/page/zone
callout!) so I went down the list and looked at gate inputs; power
supply checks (6 supplies all threshold checked), cover in place,
a bunch of random logic for zero RPM, temp difference (fixed to
removable), heads HOME, blah blah -- turns out it was the fromt
panel LOAD/READY switch! It drives an RS flop but the grease in
the rocker switch hardened/corroded so it was a two position
OFF/OFF switch. Disassembled, cleaned, LOAD/READY worked.

Got proper LOAD state, turned to READY, spindle spun up, brush
cycled, ... no head load.  ALl the logic was OK and saw the
RNENABLE or whateveritwas command, just didn't move. The linear
motor had acquired stiction from sitting. I took the dust cover
off, EXTREMELY CAREFULLY extracted the head assembly about 1/8"
'til it clicked the HOME microswitch, a few times, it loosened up.

Reassembled, READY, spinup, brush, head load.... CRASH. Top
surface of the fixed disk unmistakably crashed.

While I had the dust cover off the first time I did look at the
heads and the platter surfaces. I didn't clean the heads (I do
have the right stuff for the job; hydroentangled sterile wipes and
99.5% anhydrous isopropyl) first, and maybe I should have looked
closer, but I saw the typical "I" shaped pole in the white ceramic
substrate, assumed it was OK.

Post-crash, there was definitely a lot of FeO on the head. Cleaned
that. Ovbious grooving on the platter; 'far as I can tell all
other (3) heads/surfaces are fine. Can't see the bottom of the
fixed but thehead remained clean.

Upon closer examination of the offending head there is definitely
something caked on it on the "far" side of the head (from where I
can reach) that won't come off with the cleaning pads. It may have
been there, but if so, it would indicate a previous crash.

Knowing that the platter was trashed, I took off the dust cover,
cleaned the platter with a new pad, and felt for large bumps, and
ran the READY sequence again. Crashed two more times then I

I'm 90% sure (...) that there was a preexisting crash, but it's
entirely possible it happened on my first power-up. Since it's sat
for so long all sorts of subtle things couldhave happened which
makes that seem likely, though I did examine it before power-up,
though probably not closely enough.

It suuuuure looks like the platters on the removable cartridge are
physically the same as the fixed platter; and since I have two
spare (three total) carts I may attempt surgery.

From [email protected] Wed Feb  2 15:02:30 2005
Date: Wed, 2 Feb 2005 15:02:29 -0800 (PST)
From: Tom Jennings 
To: "General Discussion: On-Topic and Off-Topic Posts" 
Subject: Re: NOVA4 6070 disk booboo

On Wed, 2 Feb 2005, Jay West wrote:

> Almost always the problem is failure to completely clean the drive; heads, 
> airfilter and ducts, all platters (both surfaces)... you've got to 
> disassemble the platters, clean and buff them, clean the head armature, ALL 
> internal cavities, etc. Ye

Not gonna do that for this machine. Not all machines deserve that
sort of attention; this one doesn't. There's only so many
mountains I can move with a spoon in one lifetime; currently, that
will be the LGP-21.

The NOVA4 got it's airducts cleaned, PS's bench checked, disk
surfaces inspected as far as I could w/o disassembly. I admit I
did not deeply examine the fixed head set (esp. the top-surface,
hardest to see).

Complete disassembly introduces it's own set of problems itself,
but for the full tilt boogie job, necessary.

> s, it could be a pre-existing crash. The above 
> would have caught that ;)

Yes, but I'd never get to it, #1, and #2 an in-place cleaning would
have got this one to the 99% point. I didn't do that.

>> Knowing that the platter was trashed, I took off the dust cover,
>> cleaned the platter with a new pad, and felt for large bumps, and
>> ran the READY sequence again. Crashed two more times then I
>> stopped.
> Yeah, I bet it did ;)

I realized it would never work again! This wasn't a subtle crash,
or the >tink< of a skip. I wanted to characterize it (by ear) after
the head and surface debridement.

> job and buff it. Remove the platter. Also break out a dial test indicator and 
> measure the runout/flatness (which you have to do when you replace it 
> anyways).

No runoff on the outer edge visible to careful scrutiny; certainly
less than .001"

> The key of course if is there is a designated servo platter, or if the drive 
> uses a glass reticule with cylinder markings on it and an optical system. I

No servo track, reticule. I will remove the fixed platter's heads,
clean out the cavity and run the removable cartridge only, at
Bruce Ray's suggestion. I'll examine and photo the bad head, see
what state it's in.  I'll leave the platter in place for now and
see if I can find part numbers and if the removable platter's
number matches.

From [email protected] Wed Feb  2 15:05:33 2005
Date: Wed, 2 Feb 2005 15:05:32 -0800 (PST)
From: Tom Jennings 
To: "General Discussion: On-Topic and Off-Topic Posts" 
Subject: Re: NOVA4 6070 disk booboo

On Wed, 2 Feb 2005, George & Oksana Wiegand wrote:

> I had a 6045 disk system (1/2 the density of the 6070) with a head crash on
> the top surface of the fixed platter about 3/4" in from the edge. One of the
> idlets that are mounted in the white ceramic head came out, so I took this
> one head assembly off but first measuring it's alignment with a feeler
> gauge, cleaned and super glued the idlet back into the head and replaced it
> with the alignment reading taken earlier. It worked, booted Ok, the damage
> must have been in the unused portion of the disk platter.

What's an idlet?

Mine's crashed in the same physical spot, likely it's track0. I
imagine it's a common spot.

I think the 6070 has double TRACK density, not bitrate density;
Bruce Ray thinks it's possible the 6070 heads are the same as 6045
heads. I'll found out later, hopefully tonight.

> Is the blower working though the filter to generate a cushion of air for the
> head to ride on? I thought this is how it works, not only for dust removal.

It is, but that's only to cool & purge. It doesn't lift. Bernoulli
& skin effect on the head does the lifting, induced by the high
surface speeds.

Tom Jennings 

From [email protected] Wed Feb  2 19:10:40 2005
Date: Wed, 2 Feb 2005 19:10:39 -0800 (PST)
From: Tom Jennings 
To: "General Discussion: On-Topic and Off-Topic Posts" 
Subject: Re: NOVA4 6070 disk booboo

OK, you all get to laugh if this is a spectacular failure, but if
it's a success, I expect flowers.

So the fixed platter is crashed. It turns out the heads were very
dirty, I was an idiot to not to take the heads *out* for cleaning.
I tried cleaning in-place, but it appeared that there was deep
scoring hard-to-see black streaks).

When I got the heads out, the black streaks, on only the
upper-surface heads (both platters) looked like grooving. Instead
it was very hard gunk/oxide.

The heads are ceramic. So I took a clean, new popsicle stick
(wood) soaked in alcohol, and scrubbed the crap off. The heads are
perfect, with zero scoring or scratches under a halogen lamp and
magnifier. Set these aside.

The fixed platter is trashed. With my calibrated eyeball (English
units) I determined that the removable cartridge has the same,
exact platter inside. Seeing how I have three of them, I took the
platter out.  This involved drilling out (GAK!) four
extreme-torque screws [100% tape seal, vacuum, etc]. Extracted
spotlessly clean platter.

Removable platter fits perfectly as a fixed platter. Zero play at
the center ring, zero runout after torquing into place.

Heads installed, loosely. There's a head-alignment procedure, but
I'll set the fixed heads statically since that platter needs a
format anyways. The upper heads I will do the alignment.

Haven't spun it up yet. My main concern, besides dirt, is torquing
the heads in their floating mount during cleaning.  But the way
the retracted heads lift, causing a HUGE torque on one side of the
head holder seems really awful, and likely swamps and tiny error I

Even if it works, I can't be too proud of fixing a problem I
caused in the first place.

From [email protected] Wed Feb  2 22:43:30 2005
Date: Wed, 2 Feb 2005 22:43:29 -0800 (PST)
From: Tom Jennings 
To: "General Discussion: On-Topic Posts Only" 
Subject: NOVA4 6070 disk

Well, it worked, but failed anyways.

The replacement and cleaning worked for the fixed platter just
fine, but I crashed the removable platter.

The fixed platter repair went as planned. The platter dropped in,
the heads cleaned and installed OK, aligned OK. The upper heads
went in OK, did the basic mechanical alignment and since they're
accessible, did a final clean in-place.

(While the bottom platter was out I wiped everything down with a
kimwipe and 99.5% isopropyl.)

I was exceedingly careful and clean, and I don't know how to
diagnose what happened. Possibly the head got canted in it's
holder during cleaning, removal or installation, no way to tell. I
went out of my way to not apply torque to the end of the head, and
it wouldn't seem too delicate; when the heads are retracted they
are lifted on one side of the carrier, which applies a lot of
off-center force.

I followed the remove/install procedures to the letter.
Iropnically, the lower platter heads seem to have floated OK so
the repair worked.

From [email protected] Fri Feb  4 00:25:04 2005
Date: Fri, 4 Feb 2005 00:25:03 -0800 (PST)
From: Tom Jennings 
To: "General Discussion: On-Topic Posts Only" 
Cc: Tom Jennings 
Subject: NOVA4 6070 disk -- whew!

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

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


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

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" :-)


(*) 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.

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