M4 9914 tape loading questions

jim stephens jwstephens at msm.umr.edu
Thu Jan 19 13:04:03 CST 2006


John Foust wrote:

>I'm tinkering with the first of the three 9-track units I acquired recently.
>This is the M4 9914, a seemingly very nice unit in that it was clean,
>powers up and acts from the front panel buttons, and that it handles 
>800 BPI as well as 1600 and 6250.
>
>Mind you, I'm old enough to still have a stack of tapes that I used in 
>college in the early 80s, but I'm not old enough to have worked behind 
>the counter with the big VAXes and UNIVAC.  I might've written a tape
>or two in person under PDP Unix, but I probably did it under the 
>watchful eyes of someone more experienced.
>
>The first time I tried to load a tape, the vacuum fed the tape correctly
>back to the takeup reel but it was not picked up on the reel.  
>The notched leader on the tape is in good shape, but it did not engage.  
>
>I unscrewed the top of the takeup reel and was puzzled.  I expected 
>to see a mechanism to hook the leader (as you see inside a DLT, 
>for example.)  The takeup reel hub is smooth.  It does have openings 
>on the lower half, and the hub is certainly part of the vacuum path.  
>Is vacuum alone supposed to grab the tape and hold it to the takeup reel?
>
>Most other times I loaded a tape, the tape didn't move smoothly back to 
>the take reel.  It bunched up after hitting obstacles along the path.
>
>I do not yet have the user or service manuals for the M4 9914.  I did find 
>several manuals for similar units (HP 88780) on Bitsavers.  I googled 
>quite a bit to find the definitive 9-track history and preservation 
>site but I haven't found it yet...
>
>- John
>
>
>  
>
first: removing the top of the reel was a bad idea.  It's parallel 
alignment to the bottom of that
reel is key to the proper function and handling of the tape.  put it 
back on very carefully and pray.

second.  the finish on the hub is such that static and air forces cause 
the tape to wrap around the
reel.  Most half inch tapes only had a twirl of the tape around the 
takeup reel once to capture
the tape.  same as with home 1/4" tapes.  In this case the velocity, air 
pressures, and the design
and alignment of the takeup reel are very carefully done (holes in the 
top of the reel to exhast the
air is key too, so hope you remember where that was.)  to make the tape 
capture on the
reel.  Fact is, it will more naturally wrap around that if you can keep 
it from doing the
accordion pile up at the entry to that chamber than anything else.

the usual failure is that the tape will not extend to the takeup reel 
hub, but will curl up or otherwise
misbehave when it is blown into the chamber.  It will have a lot of non 
laminar flow of air from
the air feed past the head, so it will be flapping there and so the 
trick is to have it have at least
the distance from the entry to the takeup reel chamber to the hub length 
of tape that is nicely
shaped, and to have a nice flat leader once it wraps.  after a few turns 
of the takeup reel
it should lock down.  The drive senses this change in motor torque and 
assumes the tape is
captured.

Sometimes all you need to do is just wipe the first foot or so of tape 
on a reel with a clean
cloth and try it again (assuming it is not wrecked or damaged). and it 
will work.

Jim



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