TRS-80 Model 4 help requested

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Feb 28 18:25:01 2003

> 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?

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

> 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...

>
> > > 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?

> 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.

> > > 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.

-tony
Received on Fri Feb 28 2003 - 18:25:01 GMT