Dear Alan,
As this topic is quite old, I 'm not sure you will really see my answer.
Anyway, if you're still interested in this machine, I can give you help, as
I'm the owner of a complete IBM 5280 system (ie IBM 5288 + two IBM 5285 +
printer IBM 5222)with full disk systems and maintenance documentation.
Let me first inform you that neither 5285 (nor 5281) are albe to work alone.
When you start them up, they try to deal with the master controller unit
(MCU) IBM 5288, on which is implemented the system.
If it can't dialog with the 5288, you'll get only three lines of characters
on the screen, which are a kind of autotest. As far as the floppy drives are
concerned, it's quite the same. Indeed, these floppy are not part of the
5285 machine, but are extensions of the MCU 5288 on your local working
station. So, when you insert a disk inside, it's absolutely normal that you
don't have any answer on your display, as once again the 5285 is trying to
send the data read on the floppy diskette to the 5288 system.
Owning a 5285 / 5281 alone has no really interest, as it's neither a dumb
terminal and won't be useful. But it's a beautiful old machine.
All this system called 5280 is dated from 1981. Mine has been working
beetween 1982 - 1987 night and day. Now I only make it work when a friend of
mine want's to see it working, as it's really worth seeing. Unfortunately,
I've broken a keyboard and noy I've only one working station instead of two,
and my printer has no more ink ribbon :-(
Best regards. Fred (from southern France )