Tandon TM 502

Tony Duell ard at p850ug1.demon.co.uk
Wed Jul 4 16:49:11 CDT 2007

> I'm guessing it is: There's an external motor in one corner of the unit; I
> can't read most of the label, but the "0.9 deg./st" that I can see would
> suggest it's a stepper.

It certainly sounds like it :-)

> > > 
> > > Where would I start in trying to diagnose & fix this drive? I have an
> elderly
> > > oscilloscope, but little else in the way of diagnostic tools (no logic
> > > analyser, for example). Or am I better off considering it scrap & trying to
> > > find a working replacement? Personally, I'd prefer to resurrect this one if
> I
> > > can.
> > I assume this is a normal ST506 interface. I'd start by looking at the 
> > signals there -- is the machine trying to select thr drive, does it send 
> > STEP pulses, and so on. At lest then you'll know which drvice (controller 
> > or deive) has the problem
> OK, that will give me something to work on, once I've figured out how to
> re-assemble the thing whilst leaving the control board accessible....

Well, all you actually need to be accessible is the inteface cabling to 
the drive. So leving the drive accessible (and even using longer cables 
to link it hup) might be enough.

> I couldn't tell you if this was a normal ST506 i/f. The control board on the
> drive has "TM600 uP 187345" printed on it; the Sirius' controller board has
> only "XEBEC SYSTEMS INC." and "Assy 104526 rev-07" as identifying marks.

Do the cables look like an ST506/ST412 interface? (34 pin control cable, 
20 pin data cable). I am pretty sure an unmodified TM502 has that 
interface, Xebec were known for making ST412 controllers, so I am 
guessing it is.

> Does any of that help at all? I've not looked for any schematics yet, I guess
> that's the next thing to do.

Somewhere (and it'll take some finding) I have my own hand-drawn diagrams 
of the floppy-drive version of the machine. No help on the hard disk 
controller, but at least I'd have the interface connector pinout.

>From what I remmeebr (and I hope I'm remembering the Sirius and not some 
other IBM-incompatible), the data bus is multiplexed with the low half 
of the address bus on the interface connector -- in other words it's a 
buffered version fo what you get on the 8088's pins. The add-on card has 
to latch the address, etc.


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