17 Feb
2002
17 Feb
'02
9:18 a.m.
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Monday, February 18, 2002 6:33 AM
Subject: Re: Destructive charities (was: STAPLES STORES...)
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.
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.....
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.
> > 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. > > 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. 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 :-). 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