Must be the alignment of the planets, favorable for old
computers...
I got the 6023 75ips tape drive working. Pretty straightforward
debugging. With Bruce Ray's hint, the first thing I checked was
the vacuum switches (there's five, one for "master vaccum supply"
and then two each (low side, high side) in each column as limit
switches) and three of them were bad. Found that out a few weeks
ago. Swapped switches around with the other drive, didn't "run".
So I got scientific (sic). I made a manometer out of a long
plastic tube, a bucket and some automotive vacuum hose, some
masking tape and a tape measure. Attached each vacuum switch to it
with a tee, and hose in my mouth as vacuum supply and adjusted
each switch as close as possible (10% spec). One was way off, the
"master supply" switch has a different setting and I had mixed
them up, from the donor.
It attempted to load, but acted strangely, sucked tape into the
buffers (vacuum columns) then THWACK the tape, then go slack.
Twice it snapped the tape! (I'm testing with a known-bad tape).
Yesterday and today I spent about two hours tracing through logic
to see why the spindle motors wouldn't move (not even for manual
unload). Traced right up to the driver amp -- no power supply!
Duh. ... turns out the DC circuit breaker popped. Sheesh.
While the breakers were popped, during testing I initiated LOAD,
and fondled the reels such that it the servo was happy,
positioning the tape loops in the buffer. Limit switches etc all
worked OK. During this though, I found that the lucite cover over
the vacuum columns wasn't sealing; it'd warped, lifting up at the
corners, leaking a lot of vacuum. For now, I taped it shut.
Resetting the breaker a few times, I determined that a logic
problem causes the two spindle motors, in the middle of the load
sequence, to rotate at high speed in opposite directions --
drawing HUGE currents, tug of war with the tape, which snaps or
wrenches into the spool. The takeup side decided that LOAD
succeeded, and was searching for BOT. The supply side decided that
LOAD failed, and was rewinding!
More servo problems. Turns out it was another vacuum leak! The
lucite cover seals one column from the other, and it was leaking.
I made a seal by wiping silicone rubber in a film about 0.010"
thick with my fingers, tapered to match the lift of the warped
corners. Tape now loads!
Now I tweaked the final servo pots, it all behaves properly.
Now that I have actual DG terminals, I plugged one on instead of
minicom on a laptop. Display works, no keyboard. Terminal wants
CTS or RTS asserted. Fixed!
Reset, self-test, try to boot the tape:
!100022L
Nothing happens.
Long story short: the cables to the disk and tape were plugged in
wrong! Ouch. Luckily, identical paddle card wiring and pinouts.
I'd removed and marked them, but managed to install them wrong
anyways! Off-by-one problem.
Power up, (disk still off), self-test, boot:
!OK 000000 !I !100022L
DTOS (diagnostic tape operating system) boots! I typed ACCEPT, it
ran some tests, then many, many tape retried, !FATAL ERROR (tape
read error). Clean head and capstan. Reboot, ACCEPT... runs! but
I halted it, powered on the 6070 disk, (cringing awaiting head
crash.... head load OK!), reboot DTOS, run ACCEPT... it discovers
the tape (duh) and disk!
ACCEPT (accept list of equipment found, run all applicable diags
one pass) ran... halted when I accidentially hit a key during
GALLOPING ROWS mem test? Seems odd...
Reboot, repeat, hands in pockets... runs many tests... I leave
running and go eat dinner.
An hour later, I find the tape slack. There's a crease in the tape
and a transparent spot (!), but no sign of a jam, I think the
transparent spot triggered BOT (likely an error). On the screen is
the DTOS exec saying "NMMD x V 3.0" which is where it loads the
tape file; it was searching... so without reset I reload the tape,
press ONLINE... and it starts searching again! It gets to
approximatel the same thickness of tape... JAM! WHACK! power goes
out!
1) The tape caught somehow, likely that crease, cross-wound on the
capstan. These reel motors are POWERFUL, likely break your finger.
That's what it tapes to swing a 5lb reel of tape at 75 ips.
2) The jam causes motor current draw to skyrocket. I've got the
terminal, CPU, tape drive, and disk, all plugged into a quadbox
extention, plugged into the (heavy duty) outlet strip on my
workbench... the little breaker on that tripped.
Well that was stupid. The disk heads were loaded at the time, but
wasn't operating (it needs formatting anyways) and I
double-checked that the head-unload mechanism (monster capacitor +
N.C. relay) worked, so it's fine. I checked.
But I likely ruined the already-creased DTOS tape (will find out
Tuesday night) and the other DTOS tape Bruce lent me won't boot;
read error.
But it was a lot of progress anyways!
I took some pictures, like the goofy manometer, I'll put 'em up
this week.
Received on Sun Feb 13 2005 - 23:54:49 GMT
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