TRS-80 Model 4 help requested

From: Al Hartman <>
Date: Wed Feb 26 18:32:00 2003

> From: Patrick Finnegan <>
> I recently picked up a TRS-80 model 4, that seems to
> have problems with its floppy drives.
> I tried swapping the floppy drives, and that time I
> got a "Diskette?" prompt if there was no disk in
> the drive, and pressing any keys didn't cause
> anything to happen. If I put a disk in the
> drive, the machine never displays anything, and
> then after 10-20 seconds, the drive light goes out.
> I tried connecting only one drive at a time, with
> the same results. If I connected a 1.2MB floppy
> that I had laying around (a Teac FD-55GFR-149-U),
> it did the same thing as if the drives were swapped.

Ok, a quick primer about TRS-80's and Floppy drives:

Unlike IBM Drives, TRS-80 drives are usually hard
jumpered for specific positions (Not always, but
internal drives are..)

What most people in the PC world don't know is that
floppy drives have an addressing scheme similar to
Master/Slave jumpers on hard drives.

They can be set to positions 0, 1 ,2 or 3. And the
last drive in the chain needs to be terminated (like
SCSI Drives).

For external drives, the drives are set to all
selects, and pins are pulled from the drive cable to
determine what position they are in. If you notice on
IBM Floppy drive cables, there is a twist between the
A: and B: connector. That twist brings the select from
the 0 drive to the 1 select pin. All IBM drives are
set to position 1 (second position).

I don't think a 1.2 mb FDD will work properly on a
TRS-80 Model IV for two reasons. The 1.2mb drive is
much more like an 8in drive than a 5.25in drive. And
transfers data at a higher rate.

Unless the drive can autoswitch to the slower 360k
data rate, it won't work on the controller.

And if you did get it to work, it has a different
Tracks per inch capability than 360k / 180k drives.

However, assuming your problem is with the floppy
drives, and not the diskette you are trying to boot...

A 360k XT Style floppy will work fine, and once you
get it booted, a modern OS like Newdos 80, L-DOS,
MultiDos, etc... Will allow you to use both sides of
the drive for 360k storage.

You can even use 720k 3.5 drives in the same way.

I know for the Model I, LNW made a Disk Doubler Board
that worked with 8in drives, and so would accomodate
1.2mb drives. I don't know if such a disk controller
was ever made for the Model IV.

If you have a PC with 360k Drive, you should be able
to run a TRS-80 Emulator and use a disk image of an OS
to make a bootable floppy in 180k or 360k format.

Let me know if I can help you in any way with this.

The Model I/III/IV was my first machine, and I'm
pretty sure I can remember a lot of info regarding it.
And I still have all my books and disks in my closet.

Al Hartman

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Received on Wed Feb 26 2003 - 18:32:00 GMT

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