Service Note: M4 Data 9914

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(a)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..."