On May 16, 16:22, Tony Duell wrote: I never saw schematics for any of the black ones; I've got the diagram for the Astec as you know. I once did have a note of what the chopper was -- or rather, I had a part number that worked. I worked for Computer Field Maintenance for a while, and we used to repair them (though they didn't actually fail very often. They seem to be pretty robust). BSR made a copy under license, but the BSR ones don't seem to be so good -- not so well regulated, for a start, so not so tolerant of overloads. All I can remember is that it's NPN, I think. I'll dig through some old files if I can figure out a way to read the old winchester backups, and see... -- Pete Peter Turnbull Dept. of Computer Science University of York