Just for anyone else coming across this, I'd say check your power supply, too. One of my Kaypros basically worked fine, hours and hours on end, with GoTek's, or even _some_ disk drives. But when it was shipped, I found that one of the TEC disk drives wouldn't reliably format. May have had trouble writing, but it seemed to be a bit random. I ended replacing the power supply (well, ended up proactively replacing 4 Kaypro power supplies). When I replaced this one, I noticed that a printer problem I was having disappeared. (Printer would occasionally be unresponsive after long idle.) Skip to, the sporadic format/writing problems of that TEC drive are also gone.