----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Monday, February 18, 2002 6:33 AM
Subject: Re: Destructive charities (was: STAPLES STORES...)
> > > Indeed. All the more reason that old computers shouldn't just be
treated
> > > as scrap metal. There are useful parts in there.
> >
> > Yes, either for experimentation/reuse or to fix other machines.
>
> Of course. I've got plenty of PCBs where one custom chip has failed. I
> keep them as a source of the _other_ custom chips on them, for example.
Precisely.
> > > I'd probably go for the old Tandons (mainly because I have a box of
dead
> > > ones...).
> >
> > I'm looking but yet to find any, they are far easier to interface to.
>
> At the risk of being flamed, original PCs and PC/XTs use them. As do many
> CP/M machines. Oh, and TRS80 Model 3 and 4. No, I am not suggesting
> raiding such machines just for the drives, but the drives can't be that
> rare...
Hmm, not many of either around here. I have a genuine XT and a TRS80 Mod 3?
4? but I don't
want the drive that bad.....
> IBM Options and Adapters TechRef, TRS-80 Model 3 service manual. To name
> but 2 manuals I have that contain said schematics. I guess there would
> have been an official Tandon service manual, but I've not seen it (yet).
Hmm, ok, thanks, I'll look into that.
> > > Did you save any of the printer's electronics? At least the output
stages
> > > should be useable.
> >
> > Got the entire board. Including all the pin and stepper drive
transistors
>
> In which case it wasn't a Sanders 12/7. That's on 4 or 4 plug-in boards
> inside. And a separate SMPSU.
No, a very old Citoh IIRC. Came from a bakery, it's about 18" high and
weighs a ton.
> > and the psu.
> > (Print head was stuffed in it)
>
> Depending on the space you have available, you might be able to use the
> printer PCB as-is. Just send it space and CR characters :-).
Did think of that, but I would prefer to have direct control over the motor,
as I think the onboard firmware will cause
undesirable effects. Realistically, the psu and driver transistors should
be all I need. I'll generate the step sequences in software, since I want
to be able to half step if necessary.
> And you're still getting 0.4V between the computer ground and the
> peripheral ground??? How much current is flowing in that ground
connection?
Miniscule, around 5ma. Just enough to be a PITA.
> I'd use an external PSU to power the 'disk drive', wired up to the 4 pin
> power connector only. Then link the ground pins on the drive interface
> connector to the ground on the computer's parallel port. What happens now?
Same story. .4v potential difference between the grounds. This should not
be so under this circumstance, so I am suspicious of the board.
Cheers
Geoff
Received on Sun Feb 17 2002 - 17:18:17 GMT