TRS-80 Model 4 help requested

From: Patrick Finnegan <>
Date: Thu Feb 27 00:06:00 2003

Ok, I've taken the time to take it apart and try a few things, still no

I wrote:

> > I recently picked up a TRS-80 model 4, that seems to have problems with
> > its floppy drives.
> >
> > The machine is a base Model 4 with 64KB of ram (I think - haven't yet
> > taken the EMF shield off the mainboard), and no peripherals attached.
> > When I powered it up the first time, with or without a disk in the
> > (bottom) drive, it displayed "Cass?" on the screen, and then I could press
> > enter to that and the "Memory size?" prompt, and get a basic prompt.

On Wed, 26 Feb 2003, Tony Duell wrote:

> I beleive that means it can't find a disk controller, so it assumes you
> have a cassette-only system.
> Try re-seating the 'ribbon cable' between the CPU board and the disk
> controller PCB _at both ends_. I would estimate that over 50% or disk
> problems on M3s and M4s come from this cable!

Aparently, the Drive 0: is bad. Replacing it with the 1: or an
IBM-branded Tandon drive from an IBM 5150 PC, it seems to try to boot from
the disk. No disk in the drive (or the disk upside down) yields a
"Diskette?" message on the display. A disk placed right-side up, which
should be bootable, gives no messages on the display after power-up or
reset. However, with a disk inserted, the drive light (and motor) turn
off after approx 7 seconds.

I tried using a boot disk that I got with the machine, and a fresh one
from a .dsk file of LS-DOS 6.3.1H from Tim Mann's web site, using Tony's
trsfmt and diskdmp. The image works with xtrs too, so I'm fairly
confident that it should work when stuck on a floppy.

> > Also, the disk I used was supposed to be a TRS-DOS (bootable) disk, but
> > it's possible that they've gone bad after so many years. Are the disks on
> > the Model 4 recorded so that I can read them on a PC (IE 48/96tpi MFM,
> > compatible with the NEC D765)? I'd like to know if I can make backup
> > images and/or see if the disks work on another machine.
> Mostly. It is standard MFM encoding (well, the TRS-80 can do FM (single
> density) too, but the M3 and M4 at least expect the boot sector to be
> double desnisty, and the standard OSes use double density (MFM) encoding
> for the entire disk.

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?

Purdue Universtiy ITAP/RCS
Information Technology at Purdue
Research Computing and Storage
Received on Thu Feb 27 2003 - 00:06:00 GMT

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:35:56 BST