TRS-80 Model 4 help requested

From: Patrick Finnegan <pat_at_purdueriots.com>
Date: Fri Feb 28 18:53:00 2003

On Fri, 28 Feb 2003, Tony Duell wrote:

> > On Thu, 27 Feb 2003, Tony Duell wrote:
> >
> > > > Aparently, the Drive 0: is bad. Replacing it with the 1: or an
> > >
> > > Does the spindle motor run on this drive when you try to boot from it?
> > > Does the LED come on?
> >
> > Sorry, guess I should have been more specific. The (drive that was
> > 0:) drive spins, and the LED comes on, but the machine still says "Cass?".
>
> OK...
>
> What test equipment do you have available? Multimeter? Logic probe? Logic
> analyser? 'scope?

"Yes." I've actually got all of those. Don't particularly like using my
DMM to observe changing signals, though... I need to find/build myself a
decent analog meter sometime.

> I can probably suggest signals to look at to find out exactly what's
> going on...

That would be most appreciated.

> > The other drive (which I had replaced it with) attempts to read from the
> > disk, and either displays "Diskette?" or nothing if there's no disk in the
> > drive or a disk, respectively.
>
> Of course at this point you don't _know_ that the disk controller or CPU
> boards are working correctly...

That's what I'm betting the problem is.. it'd be nice to be able to rule
out the drive controller and CPU board.

As per your suggestion yesterday, I'll try swapping the RAM banks to see
if the RAM is having difficulties.

> > > > IBM-branded Tandon drive from an IBM 5150 PC, it seems to try to boot from
> > >
> > > What have you done about the termination resistor pack (the 'odd coloured
> > > IC' on the drive logic board)? The machine will not do the right things
> > > if the last drive on the cable is not terminated.
> >
> > Maybe this is part of the problem. Neither drive has a terminator on it.
>
> Are you sure? It normally goes in a DIL socket near the interface cable.
> Is there a totally empty socket on both drives?

There's a SIP socket pretty much 'on top of' the I/O connector. I don't
see anything else (DIP shaped) on the board that isn't a 'normal' black
plastic IC. I'll check again, but unless it's mounted inside the drive...

> > What resistance is it? I could probably try making one out of spare
>
> 150 Ohms, but I can't remember if the resistors are separate or if they
> have a common connection to the highest-numbered pin on the package. I
> think the former.

OK, I think I have one of those laying around, with a common pin. If the
RAM swapping doesn't help, then I'll finding a terminator pack to stick in
there. Oh wait, I have one right here from a SCSI drive. Yes, testing it
with my handy-dandy crappy-DVM, it's 148ohms. I might try this first.

> > > > I would like to try to make an image from the disks I have, is there a
> > > > program that works under Linux with a standard floppy disk controller to
> > > > read disks and spit out .dsk files?
> > >
> > > I've not written one yet (although it would not be hard to do). However,
> > > I belevie xtrs can do this (BACKUP from a physical disk to an emulated
> > > one). Since I don't run X, I can't be sure, though.
> >
> > I haven't seen anything in xtrs that lets me use a physical disk, only
> > disk images. Does anyone know if I'm mistaken and xtrs will read disks?
>
> I have the source of an old version on this machine. I can't run it,
> because I don't run X, of course, but a quick grep shows a number of
> FDRAWCMD ioctl()s in trs_disk.c. Which implies to me that it's accessing
> the PC disk controller at a low level, to read a non-native (for the PC)
> disk format, presumably a real TRS-80 disk.

The help for xtrs didn't seem to indicate that, but I'll try and play with
xtrs when I get back home.

Pat
--
Purdue Universtiy ITAP/RCS
Information Technology at Purdue
Research Computing and Storage
http://www-rcd.cc.purdue.edu
Received on Fri Feb 28 2003 - 18:53:00 GMT

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