Elanman99 wrote on 2025-07-23, 09:27:

but all my attempts to make the required Compaq 'Diagnostic' floppy have failed.

Although I've never created a diagnostics disk for this specific Compaq model, I remember that there isn't any particular difficulty with the process so more information is needed please.
What have you tried to create the disk and how does it fail exactly? Do you have an SPxxx.EXE file or a disk image? Can your floppy drive write DD disks?

My SLT286 has a Citizen 3.5" drive which I understand is a 1.44Mb but a bit of an oddity as it has a 26pin connector. I dont think the drive is faulty because if I try a DOS 6.2 boot disk it starts OK, reads the disk, shows 'Loading MS DOS...' and then hangs.

To create a 720K boot disk I have an XP machine with 1.44 drive and a couple of real 720Kb floppies as well as several 1.44Mb floppies. Using command line settings I was able to successfully make just one 720k formatted disk (on a 1.44 disk). My experience seems to be exactly the same as Catbones, Reviving a Compaq SLT 286 with a (longish) thread that documents almost the same as what I have tried.

The reply to this short thread give the SP0308 file I used
Help getting Compaq Diagnostics/Setup floppy image on real floppy?

The files were written to the 720k formatted disk by QRST.exe which itself is extracted from the SP0308 file. The diagnostic files are all now on the disk, but its not bootable.

Ian

So you don't face any problem while creating the disk following the normal and intended way, it just doesn't boot from it. At this point, and given that you weren't able to boot from another dos disk too, I'd make sure that the computer can boot from something, anything. Maybe it's not the disk but the drive/computer and buying a new disk won't help.

Ideas to try:
-Use some virtual machine/emulator (like pcem, 86box, virtualbox...) or another old pc and boot from the disk you created. If it works then the disk is not the problem.
-Try other dos boot disks like v3.3 to see if anything works.

Also, make sure the drive is the intended type/density for that boot media.

286 is genuinely old enough to have low density drives.

A high density boot disk naturally will not work, since the drive cant actually seek to tracks that small, and the head's sense area is too large.

If it's a 3.5" drive, look inside the flap to check for little vertical spikes at the extreme sides of the flap.

Low density will only have one on the right. (It checks for the write protect hole) High density will also have one on the left. (Checks for the disk medium ID hole)

Write a diag disk set of the appropriate type.

Some low density drives 'have problems' reading media formatted/made in a high density drive, due to the 'head too small' issue.

Another diagnostic step is making the diag disk in a low density drive.

The Sp0308 disk is not bootable ! You need a DOS 3.3 boot disk as konc mentioned, or maybe a DOS 5 boot disk to boot from then run the Setup.exe off the diag disk.
minuszero has a disk image: minuszerodegrees.net/software/Compaq/sp0308_720k.imz

konc wrote on 2025-07-23, 12:08:

So you don't face any problem while creating the disk following the normal and intended way, it just doesn't boot from it. At th […]
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So you don't face any problem while creating the disk following the normal and intended way, it just doesn't boot from it. At this point, and given that you weren't able to boot from another dos disk too, I'd make sure that the computer can boot from something, anything. Maybe it's not the disk but the drive/computer and buying a new disk won't help.

Ideas to try:
-Use some virtual machine/emulator (like pcem, 86box, virtualbox...) or another old pc and boot from the disk you created. If it works then the disk is not the problem.
-Try other dos boot disks like v3.3 to see if anything works.

A s I understand it, these Compaq machines will only boot off a standard boot disk once the BIOS has been set using the Compaq diagnostic floppy. BIOS I think has parameters settings for hard and floppy drives.

Ian

Horun wrote on 2025-07-23, 14:04:

The Sp0308 disk is not bootable ! You need a DOS 3.3 boot disk as konc mentioned, or maybe a DOS 5 boot disk to boot from then run the Setup.exe off the diag disk.
minuszero has a disk image: minuszerodegrees.net/software/Compaq/sp0308_720k.imz

As you say, SP0308 is not bootable, its just part of the route to getting the diagnostics disk

Ian

Horun wrote on 2025-07-23, 14:04:

The Sp0308 disk is not bootable ! You need a DOS 3.3 boot disk as konc mentioned, or maybe a DOS 5 boot disk to boot from then run the Setup.exe off the diag disk.
minuszero has a disk image: minuszerodegrees.net/software/Compaq/sp0308_720k.imz

The image from minuszerodegrees might not be (I don't know, I didn't check), but running the self-extracting SP0308.EXE @Elanman99 used and then QRST.EXE does create a boot disk which boots to this screen

Elanman99 wrote on 2025-07-23, 15:44:

A s I understand it, these Compaq machines will only boot off a standard boot disk once the BIOS has been set using the Compaq diagnostic floppy. BIOS I think has parameters settings for hard and floppy drives.

Well if you have this information (I don't disagree, I just can't confirm it) then your next step should be checking if the disk you created boots. Not in the Compaq, somewhere else. In another computer or mounted to an emulator or virtual machine. If it does then the disk is not your problem and getting another won't solve anything.

konc wrote on 2025-07-23, 16:37:

Horun wrote on 2025-07-23, 14:04:

The Sp0308 disk is not bootable ! You need a DOS 3.3 boot disk as konc mentioned, or maybe a DOS 5 boot disk to boot from then run the Setup.exe off the diag disk.
minuszero has a disk image: minuszerodegrees.net/software/Compaq/sp0308_720k.imz

The image from minuszerodegrees might not be (I don't know, I didn't check), but running the self-extracting SP0308.EXE @Elanman99 used and then QRST.EXE does create a boot disk which boots to this screen

Good to know, thanks ! I only peaked inside the .imz and didn't see any recognizeable boot files 🙁