14 Oct
1999
14 Oct
'99
2:20 a.m.
One thing, the drive never really seems to *look* for
the BOT marker. I
mean, pressing load causes the drive to immediately rewind a good 8"-1' of
tape and then stops there. Nothing else.
It's possible that the optical sensors in the tape path are out of
adjustment or simply just dusty. Most tape drives have at least
two sensors, one for the BOT and one for the EOT marker, and some have
a third sensor for "tape present in tape path". If these are giving
nonsensical combinations, (for example, both BOT and EOT at the same time)
the machine is likely to do weird things or fail its self-test.
In some cases, bright light (i.e. direct sunlight) shining into the
tape drive will temporarily screw up these sensors, leading to the classic
stories of "tape drive works in the morning but not in the afternoon"!
--
Tim Shoppa Email: shoppa(a)trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
7328 Bradley Blvd Voice: 301-767-5917
Bethesda, MD, USA 20817 Fax: 301-767-5927
14 Oct
14 Oct
5:50 p.m.
A little update on my progress...
I think that I've determined that it's a tension problem. The BOT/EOT
sensors are working fine, and I logically (or otherwise) deduced that it
reads that there's a tape present when both sensors are *not* getting a
reading at the same time (two sensors side-by-side, the adjacent piece on
the media side is highly-polished - i.e. reflective - aluminum).
An incidental post to the HP3000 mailing list about a guy fixing the
tape tension on his system using DirtDevil vaccuum belts prompted me to
run to Target and pick up a couple, as the rubber on my capstan was badly
glazed. On they went, and I got the machine in really bright halogen light
so I could watch it closely. Bingo! The tape slacks *badly* when you push
load, right below the head assembly and right above/around the capstan.
But why? (And how did I miss that before???)
I have a small idea, but I don't know enough about the general mechanics
of tape drives to really figure it out. Here's the deal: the capstan is a
little over an inch in diameter and has a flat ring behind it (toward the
backplate) that extends about an eigth of an inch beyond the radius. This
disc is white with uniformly-spaced black dots, around a quarter-inch
apart, going all around it. Like timing marks for a strobe? Positioned
directly behind the path of the dots, recessed in the case, is a small red
bulb. And it's dead.
Could it be that it is somehow supposed to read the rotational speed of
the capstan from these dots and the sensor/light emitter is dead? Do these
things work this way? I know the servo for the capstan is working fine,
testing it by fooling the sensors into thinking a tape is threaded and
pressing load makes it spin strongly (no slipping when I trail a finger on
it).
Ugh, unfortunately I left my vom at work and can't check if there's
current to the bulb during the load procedure. I'll check tomorrow night
and let you know...in the meantime does anyone have any ideas/comments?
Thanks for everyone's input so far, it's been invaluable.
Cheers,
Aaron
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