Maintaining and hooking up a Mitsubishi M4853 Floppy Drive to a modern PC

[BogdanV]

I once had an external dual floppy drive unit from my Tulip but only one unit seems to actually work. I cleaned its head with izopropyl alcohol, hooked it up to a K6-2 PC and inserted the only 5.25 inch floppy I had (a Misco Colour Plus, 1.6MB diskette if it matters). I set it up as a 1.2MB 5.25inch drive in BIOS (highest available capacity) and booted into Windows. I got a floppy disk fail error (40) during POST but it seemed functional nonetheless.
In Windows 98, it tried reading the diskette but said that it wasn't formatted. Format (quick and normal) failed though.
Probably the diskette is long dead and the drive is functional.

One other oddity is the fact that the DS jumper was set to 1 (as it came out of a dual floppy unit) BUT when connected alongside my 3.5inch floppy it showed up as drive A. Setting it to DS 0 caused a "Device not ready" error to pop-up when accessing the drive.
There also seems to be an array of unmarked pins on the unit. On the faulty 5.25inch drive that was set as DS 0, that array was filled with jumpers. On the functional one, with DS 1, those pins were unjumpered (if that's a word). Any idea on what purpose do they serve ?

I probably need to get my hands on a batch of (hopefully working) 5.25inch diskettes but until I manage to do that, I'd like to completely rule out the possibility of a configuration error on my side.

What do you guys think ? Could there be a configuration error I didn't notice ?
Also, if anyone happens to have any scanned manuals and is willing to share them with me, I'd be grateful !

 

[Chuck(G)]

I've got at least one of the buggers in my stash. If you'd like, I can check it out for you.

 

[k2x4b524[]

Set your bios to recognize a 720kb 3.5" floppy disk. the 4853s are 720kb in nature (I believe), despite being 5.25" it will probably work just fine like that.

 

[BogdanV]

@Chuck(G) That would be awesome if you can.
@k2x4b524[ Haven't tried that. I'll give it a shot, although, if the floppy diskette is dead, I probably won't be able to tell the difference haha.

 

[SpidersWeb]

One other oddity is the fact that the DS jumper was set to 1 (as it came out of a dual floppy unit) BUT when connected alongside my 3.5inch floppy it showed up as drive A.

When using a twisted floppy cable (I'm guessing you are in your modern PC), both drives should be set to DS1.
The twist in that cable reverses the drive select lines.

If both are set to DS1, the drive at the end of the cable will always be A, and the one in the middle will always be B.

 

[BogdanV]

Ah so that explains it ! Thanks for the info.

EDIT: I posted the same message once but it failed to register. Sorry if it ends up in a double post.

 

[vwestlife]

inserted the only 5.25 inch floppy I had (a Misco Colour Plus, 1.6MB diskette if it matters)

That's a high density disk, which will not work in a 720K 5.25" floppy drive because it requires a stronger magnetic field to format, as shown in the chart below. You need to use a double-density disk, preferrably rated at 96 tpi, but ordinary 48 tpi "360K" floppies should work fine as well.

8" all formats: 300 oersteds

5.25" double density (360K): 300 oersteds
5.25" quad density (720K*): 300 oersteds
5.25" high density (1.2MB): 600 oersteds

3.5" double density (720K): 665 oersteds
3.5" high density (1.44MB): 720 oersteds
3.5" extra-high density (2.88MB): 900 oersteds (unconfirmed)

* as used by the Tandy 2000 and other non-fully-IBM-compatible MS-DOS machines

 

[BogdanV]

UPDATE:
I managed to get a hold of a stack of 360K floppies and succeeded in writing MS-DOS 3.30. How I managed to do it was kind of convoluted because rawwritewin didn't want to work with the 5.25 drive and WinImage always triggered an illegal operation error when trying to write to disk (all versions from 3 to 7).
Alas, what I did was extract MS-DOS to a folder, use dosver to spoof DOS version from 6.2 to 3.3 and run the MS-DOS 3.3 version of format with /4 /s. I then proceeded to manually copy all DOS files to the diskette. So far so good...

Except that BIOS refuses to boot from it.
Whatever I tried, I couldn't get that "Floppy Disk(s) Fail (40)" error to go away. It DOES work however because I just managed to write DOS 3.3 on it but it just won't boot.

I removed the 3.5 drive and left the 5.25 as the sole floppy drive. Also switched the jumper to DS0 (since its alone). This didn't help.
Tried setting the drive in BIOS either as a "360K, 5.25inch" drive or as a "720K, 3.5inch" as someone suggested before. This didn't help either.

Am I missing some kind of obscure jumper configuration or is it something blatantly wrong and obvious that I'm doing here?

 

[MikeS]

How I managed to do it was kind of convoluted

Sounds like it...
I didn't get why you had to mix DOS versions?

I removed the 3.5 drive and left the 5.25 as the sole floppy drive. Also switched the jumper to DS0 (since its alone). This didn't help.

Not surprised; read post #5 again (in a PC all drives must be set to DS1).

Am I missing some kind of obscure jumper configuration or is it something blatantly wrong and obvious that I'm doing here?

Could be; lots of possibilities...

 

[BogdanV]

Sounds like it...
I didn't get why you had to mix DOS versions?

Because the programs run a version check and if that fails, they simply blurp something along the line of "Wrong MS-DOS version". Simply running DOS 3.3 utilities on 98/DOS6.2 doesn't work.

Not surprised; read post #5 again (in a PC all drives must be set to DS1).

I might be dense but if the unit is alone, what's the point? There's nothing to switch around if there's only 1 floppy drive on the entire ribbon.

 

[Chuck(G)]

Because of the peculiar way that IBM decided to assign pins on the FDC connector, all drives are the second drive select. The twist in the cable for the first drive not only swaps drive select pins, but also adds an extra motor control pin. On older machines where all floppies are on a "flat" cable (no twists), each drive has a different drive select, but there's only a single motor control line shared among all drives. Turn one motor on, they all come on.

There were a few third-party FDC/HDD cards that could be jumpered for the "flat mode" and have 4 drives on a single floppy cable.

 

[BogdanV]

Thanks. I can see the reasoning behind it but truthfully, without knowing about it, it sure seems counterintuitive. I'll switch it to DS1 but I'm not keeping my hopes high.

 

[Chuck(G)]

Even more confusing is drive-select labeling. Some manufacturers decided to use DS1-DS4 labeling; others used DS0-DS3. They're all the same electrically; only the names have been changed to confuse the innocent.

 

[MikeS]

Because the programs run a version check and if that fails, they simply blurp something along the line of "Wrong MS-DOS version". Simply running DOS 3.3 utilities on 98/DOS6.2 doesn't work.

I got that, but why not use 6.2x in the first place?

I might be dense but if the unit is alone, what's the point? There's nothing to switch around if there's only 1 floppy drive on the entire ribbon.

As a matter of fact, as Chuck explained there is nothing to switch around whether there's one drive or two; on a PC a drive will work equally well as drive A or drive B without changing any jumpers, but that does require that all drives be set to DS1 (and the cable has a twist).

 

[BogdanV]

I got that, but why not use 6.2x in the first place?

Because, afaik, the boot sector has changed from 3.x to 6.2, which makes Win98's FORMAT.COM useless in this case.

Ok, the floppy is now on DS1, still getting that "Floppy drive(s) fail (40)". Apparently MS-DOS also fails to access it, which means that only Windows 98 can actually see and read/write to it. How on Earth is MS-DOS capable of working with the floppy from Win98 but not natively, I don't know. Possibly because of the way thunking is handled I guess.

 

[MikeS]

Because, afaik, the boot sector has changed from 3.x to 6.2, which makes Win98's FORMAT.COM useless in this case.

Another different FORMAT program? Now I'm really confused; just what are you trying to accomplish? Even if you do get the drive working it won't be compatible with anything in the PC world.

How on Earth is MS-DOS capable of working with the floppy from Win98 but not natively, I don't know. Possibly because of the way thunking is handled I guess.

Huh?

 

[BogdanV]

Okay, I think neither of us actually understood eachother xD

Let me try to rephrase this.

1. What I seek to accomplish:

A. Successfully hook-up a Mitsubishi M4853 Floppy Drive to a PC with a AMD K6-2 CPU.
B. Write a bootable 5.25" diskette with MS-DOS 3.3
C. Plug the floppy drive back to my Tulip System I 8086 PC-compatible and boot off that diskette

2. What I have accomplished so far:

A:
Set up Mitsubishi M4853 Jumpers on the following pins: DS1, HS, H1R2.
Connected Mitsubishi M4853 Floppy Drive to a PC (that's the one with a K6-2).
Set up Mitsubishi M4853 Floppy Drive as "Drive A: 360K, 5.25inch" in BIOS settings.
POST shows "Floppy drive(s) Fail (40)".
MS-DOS 6.2 (part of Windows 98SE) shows "Error reading drive A: Abort, Retry, Fail" when trying to access A:
Windows Explorer from Windows 98SE can read, write and format to the 5.25inch drive.

B: Got a hold of a MS-DOS 3.3 5.25inch floppy disk image file from BetaArchive
Tried writing the image to a 5.25inch floppy using RawWrite: program refused to work with the drive
Tried writing the image to a 5.25inch floppy using WinImage v3: writing to diskette triggered an Illegal Operation Error, thus crashing the program.

Manually extracted MS-DOS 3.3 from the floppy image and dumped all files in a folder.
In order to make a floppy diskette bootable, one needs:
1. A boot sector compatible with whatever Operating System you want to run from it
2. The actual Operating System files you want to boot
For Point1:
FORMAT.COM can format and write to floppy boot code compatible with its own MS-DOS version (ie. FORMAT.COM from MS-DOS 6.2 can write MS-DOS 6.2-compatible boot code BUT NOT MS-DOS 3.3-compatible boot code)
Windows98's FORMAT.COM can not write MS-DOS 3.3 compatible boot code, thus one needs an older version of FORMAT.COM - the one I just extracted from the MS-DOS 3.3 disk image.
DOS3.3 FORMAT.COM cannot run due to DOS version mismatch. Temporarily spoofing Win98's DOS version from 6.2 to 3.3 (using the dosver freeware utility) solved the problem.
For Point2:
Formated a 5.25inch diskette with MS-DOS 3.3-compatible boot code, then copy-pasted all MS-DOS 3.3 system files over.

And this is where I am right now. Before proceeding to C., I wanted to try and make my PC boot from the 5.25inch drive as a test to make sure everything works properly.

I sincerely hope this is clear enough. If not, then either my English is fubar or my brain is, for I honestly fail to see what was unclear in what I previously wrote. I'm not saying this as an insult, just that I really fail to see what was wrong in my wording.


And the last issue...

How on Earth is MS-DOS capable of working with the floppy from Win98 but not natively, I don't know. Possibly because of the way thunking is handled I guess.
Huh?

Like I already said, trying to access the 5.25inch drive from DOS directly, natively (ie. "Reboot to DOS" / "Command Prompt Only" boot option if you hold down CTRL) throws a "Error Reading Drive A: Abort, Retry, Fail?" error.
Opening a DOS prompt from within Windows98 (ie. WIN+R + "command") and accessing the floppy works. Likewise, accessing the 5.25inch drive from Windows Explorer also works perfectly.

So, what is the difference then? As you know, a DOS session running inside Win9x is different from one running natively on bare metal. DOS sessions are created and managed by the Virtual Machine Manager, with 16-bit DOS calls being thunked by the system. What I believe is that somehow Win98 is smart enough to compensate whatever wrong settings there are and help DOS properly access the floppy drive because DOS depends on VMM to handle its calls.

 

[Chuck(G)]

You do realize that the M4853 is a 720K floppy, (96 tpi) don't you? So, shouldn't you set it up in your BIOS as 3.5" 720K? (the actual physical media size doesn't matter)

 

[Malc]

A long time ago i used M4853 drives on My BBC Micro and swapped between my PC and the Micro ( obviously switching jumpers ) Is there another number ie: M4853 - ??? or any other details on the plate ?, I should have my notes on the drives i used and will see if i can find them.

 

[BogdanV]

You do realize that the M4853 is a 720K floppy, (96 tpi) don't you? So, shouldn't you set it up in your BIOS as 3.5" 720K? (the actual physical media size doesn't matter)

Tried that. Didn't change a thing.