In message <150A878A7B7E(a)ifrsys.com> classiccmp(a)u.washington.edu writes: Have you tried Tandy/Radio Shack National Parts? At one time they sold service manuals for all their computer stuff, and such manuals almost always contained schematics/data on the 'bought-in' parts -- things like PSUs, drives, monitors, etc. IIRC if the stock number for the device was 26-abcd, then the service manual was MS260-abcd. At least in the UK, they were available to the general public. There may also have been a Technical Manual (which would have had a different stock number), but I doubt it. Talking of Tandy stuff, I bought a second-hand Model 4 last weekend. Does anyone know where to get a Technical Manual for this machine? What I really need is a list of Supervisor Calls, Docs on the I/O ports, and a schematics of the CPU board. I believe I have a 'gate array' board - there's a 40 pin chip with a Tandy custom number next to the Z80A. I'd be quite happy to buy the entire technical manual if it's still available anywhere, but I do already have the Model 3 manual, so I don't need any info on the disk drives/controller, RS232 board, PSU, or monitor. Anyway, with this machine I got a Cummana hard disk unit. Cummana were a UK company who later went on to make disk drives for the Acorn BBC micro. This unit contains a Shugart 612 disk (any ideas?) a Western Digital controller (I can't remember the number, but it is a standard card), a PSU, and a little address decoder/interface board. Maybe you have an original Tandy version of that. -tony