HP 9121 9122 drives

I have the ofifical service data for the 9121, it is useless. The only schematic is for the trivial linear PSU section. One day I'll get round to tracing out schematics for the 9121. I can't do the 9122 as I don't have one. There are schematics for the double-sided drive (used in the 9122, at least the double-denisty version) on the HPCC CD-ROM, in the 9114A or Integral diagrams. What's the problem with your units? Most of these HP controllers follow much the same design with a 68B09 running the show, a little bit of RAM and EPROM, a Western Digital controller chip, 8291 GPIB chip, etc. Actually, most of the problems are mechanical and relate to dried-up grease on the eject mechanism. If you don't catch this in time, the disk holder is not latched correctly when you eject the disk and, on the double-sided units, the upper head is ripped off the gimbal spring. You have been warned! -tony