Misaligned tape heads. SERIOUS data-loss possibility.

[Scott Dorsey]

In article <1991 at brchh104.bnr.ca> karim at uncecs.edu (Omar A. Karim) writes:
>I am wondering if anyone has a fix to this rather dangerous scenario:
>1 Tape head gets misaligned. No symptoms, backups continue as usual, errorfree.
>2 Tape drive crashes IRRETRIEVABLY, system crashes......
>3 Replacement drive cannot read your DUMP tapes. 

On a nine-track drive, this is easy to do.  I assume that your problem is
not with horizontal alignment but solely with azimuth, though if you have
a horizontal problem it's not difficult to do with the proper alignment
tape (or even with Magna-See and a micrometer).  First, put a dual trace
scope on the output of the preamps for the inner and outer tracks (being
careful to put them before any demod stuff), and start running a
known-good tape on it.  Adjust the head so that it's perpendicular to the
tape by matching up the phase of the two square waves.  You'll notice the
corners squaring off as well, as the high frequency response improves.
There, your azimuth is correct.  Now, if you have a bad tape that was
recorded at a slant azimuth, you can readjust the head so that the azimuth
of the head matches that at which the tape was recorded (although you'll
note that the wave will never square off as well, due to the length of the
gap).  Read the tape, and then be sure to put the machine back into
correct alignment so that you don't write any tapes incorrectly.  I know
nothing about the 1/4" tape cartridges, but if they have multiple tracks
this method should work.  You'll probably find that the azimuth is less
critical as the track width decreases and the tape speed increases, and
more critical as the density increases.  --scott

   Of course, the real fix is to 
     A. Align your heads regularly
     B. Clean heads every time you mount a tape