Service Note: M4 Data 9914

From: Bruce Lane <kyrrin_at_jps.net>
Date: Mon Jun 8 08:21:57 1998

        Although the hardware I'm mentioning is not in itself 'classic,' the
technology of 9-track tape certainly is. Forgive me if this seems
off-topic, but I'm trying to spare anyone else lucky enough to nab one or
more M4 Data 9914 tape drives some grief.

        There is a potential problem spot in the early production (pre-1992, as I
recall) power supply boards to watch out for with these drives. The +12
rail is supplied by an LM350 in a TO-3 case. The leads from the 350 are
joined to a three-pin Molex connector that is then plugged into a matching
male header on the regulator board.

        I've seen two failure modes in this design to date.

        1). Failure of the regulator. Symptoms include initial startup OK,
followed by the +12 rail dropping to about 8.4 volts after no more than
three minutes. If the regulator output is examined with an O-scope, one
will see an AC potential of about 1.6 MHz at nearly two volts peak-to-peak.
Also of note is that the regulator gets a lot warmer than normal, as does
the bridge diode module supplying the regulator's input.

        I've been told by M4's service department that the most common fix for
this is to replace capacitor C10 on the regulator board. There is also an
alternative cure, specifically replacing the LM350 with a Motorola MC78T12
in a TO-220 case (doesn't seem to be available in a TO-3).

        Note that it is CRITICAL to use the 78T12, not a standard 7812. The 'T'
version has an output current rating of 3 amps, vs. the 1A rating of the
standard 7812. The +12 rail in these drives pulls about 2A under normal
operation.

        2). Poor contact in the three-pin connector, which results in overheating
and connector burning. I saw this in the drive I got most recently. Since I
lacked a suitable replacement connector, I merely removed the male header
and the burned female connector, and then soldered the wires directly to
the pads.

        Post-1992 drives have, I'm told, a completely redesigned power supply that
addresses these issues.

        Caveat emptor!


-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Sysop, The Dragon's Cave BBS (Fidonet 1:343/272)
(Hamateur: WD6EOS) (E-mail: kyrrin_at_jps.net)
"Our science can only describe an object, event, or living thing in our own
human terms. It cannot, in any way, define any of them..."
Received on Mon Jun 08 1998 - 08:21:57 BST