WTB Miniscribe 3425 (working or parts donor)

Mark J. Blair nf6x at nf6x.net
Tue Nov 24 22:45:45 CST 2015

I have an aftermarket hard drive system for the TRS-80 Color Computer. It includes a Miniscribe 3425 5.25" hard drive and a Xebec S1410 SASI disk controller. This Miniscribe hard drive has a stepper motor positioner, and Miniscribe actually sprang for an optical track 0 sensor... unlike the 3.5" Miniscribe 20M drive in my first Amiga hard drive system, which simply slammed the stepper against a hard stop to find track 0. I'd like to image this drive with the MFM Reader/Emulator card if I can get it to work. Actually getting the whole system working with one of my CoCos would be even cooler, of course. I have no idea what might be on the hard drive; it was an eBay purchase, back when eBay and I were still on speaking terms.

The hard drive is blinking an error code on its LED, reporting that it cannot cover the track 0 sensor. Measuring the sensor pins with a DMM while the drive is powered makes me believe that the optical sensor itself is working correctly. Its output disappears into a Miniscribe-marked, presumably custom IC, so I don't have high hopes of debugging this further within the bounds of my gumption.

Interestingly, the interruptor on the external stepper shaft appears to cover the sensor on the final step against a hard stop, so it's not clear why this drive even needs the sensor. 

Does anybody have a donor Miniscribe 3425 available for sale or trade? The heads can be rattling around in drifts of aluminum filings for all I care, as long as the logic board is somewhat likely to be functioning. Or maybe has one sitting around that they might like to loan to me to image for them, and they don't mind if I risk board swaps after making a valiant effort to get the data off their drive for them first?

So far, I've only used my new MFM Reader/Emulator to image and emulate a Tandon TM503 in a Tandy Fifteen Meg Disk System, and it worked wonderfully in that role.

Mark J. Blair, NF6X <nf6x at nf6x.net>

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