View Full Version : Atari-Compatible 3.5" Floppy Drives

January 29th, 2016, 09:14 PM
Is there a master list? I'd like to source the cheapest DD drive possible (unless for whatever reason an 1040ST F can somehow take a standard 1.4mb PC floppy drive - which I seriously doubt). Was there compatibility beyond Atari? The interface is 34-pin, which suggests (without research) it could be Shugart; and the 4-pin power adapter is also standard.

Sadly after painstakingly making a VGA cable and InPort Mouse adapter, I've confirmed my floppy drive doesn't work. I get 'target disk unusable' and also that the drive isn't responding. I know nothing about the machine's pedigree so I don't know if someone altered jumpers or something. The drive tries to read both on boot and when I try to format or open the drive. I also tried cleaning the heads with no success.

Maybe I'll try something like this http://eab.abime.net/showthread.php?t=71760 (I don't think I have that drive, though).

January 29th, 2016, 10:44 PM
You can use any PC Drive. Just jumper it to DS0. Just Link the Atari's floppy signals 1:1 to the drive. The lowest Drive select signal of the Atari must be connected to the lowest drive select signal of the drive.

January 30th, 2016, 12:07 AM
incidentally the Atari may very well have used Shugart drives in the beginning (or whenever). Remember the original ST floppy drive was single sided 360k. Later it became double sided 720k. Not sure when, but the TT or something used 1.44 mb drives (I think). There are replacement bare drives on eBay. In fact atarifreak in the UK has at least 1 type (Shugart if I recall), maybe others, or at least had others.

The floppy drive emulators seem to be the way to go though. Not only do you have to find a drive in good condition (granted you may be able to source NOS), but also media. I want to write a book LOL on an Atari ST. I contemplated on the Mac, but nah, I like Ataris better. I probably won't fully entrust the manuscript to any media, except hard copy, but sd/mmc cards rate higher and more reliable then old floppies/drives.

The drive emulators are open source. There's a recent thread from the past week which has the link to most of what you'd need to build one, if you don't want to buy one. In "General" discussions.

January 30th, 2016, 06:54 AM
I appreciate the info. I'm not an ST guy, so I don't want to spend a lot. Are you saying I can put a standard HD FDD drive in place of the DD drive without altering the controller setup (I assumed that wasn't on the drive itself)?

January 30th, 2016, 07:11 AM
Just about. The ST has a couple of quirks. It really wants a Disk Changed signal (yes this is an ST page) and many disks have this. If not you can cludge it...


and it needs to be a fairly low power CMOS drive. The drive will just about work without the disk change but you risk corrupting a disk...

January 30th, 2016, 07:12 AM
Actually all 3.5" drives are low power. You can also use a 5.25" drive but that does need to be CMOS...

January 30th, 2016, 09:36 AM
Yeah I didn't totally understand the above discussion I'm afraid, so I need some more guidance. But I've also learned some stuff about my particular machine: 1) the problem is somewhere in the drive. Once I removed the drive, the slow boot-time dissipated and it boots immediately from ROM. 2) No drives showed up, so it is also actually detecting the drive and I think it's detecting it as a DD drive because there's an A and B drive that both disappear. 3) It doesn't recognize my HD floppy drive: NEC FD1231M.

This might be the solution: http://www.amigaportal.cz/forum/showthread.php?t=5478, so hopefully Google Translate does well with Czech. So... pin 19 of the IC to pin 10 of the floppy (middle wire in the picture); cut the trace to pin 34 [of floppy, hereafter] and connect it to pin 1; connect pin 34 to TP15 on the board. It looks like that's it. I'm a little concerned about the trace cut, though.

January 30th, 2016, 10:01 AM
Slow boot with no disk in drive is normal.

The ST does not know if the drive is single or double sided, it just knows its a drive.

What condition is the drive belt in (If it has one).

Seeing "A" and "B" is also normal. TOS will tell you to change the disk in the drive if you click on "B". Allows you to copy disks on a single drive machine.

Can you put any diskette in the drive and try formatting it to 360K? (a 1.44 will usually format).

If that works leave the disk in the drive and re-boot.

For testing you don't need the disk change.

January 30th, 2016, 10:07 AM
Remove the drive cover and see if you can find something like a blown capacitor or loose chip. Find damage, fix same, maybe it will work.

Otherwise you will need a replacement:
1) Get the Epson SMD-380 (or its high density counterpart SMD-300). Double check jumpers and plug it in.
2) Follow one of the online instructions on how to tweak a normal floppy drive into one that is acceptable to the Atari.
3) Buy a replacement drive or kit that is already setup for Atari usage. The only website I found selling these parts is in the UK and charges 15 pounds for the drive and 25 pounds for a HD controller. Shipping would be a killer so maybe you can find a US counterpart.

Check out http://atariage.com/forums/topic/208904-atari-st-floppy-drive-repaired/ for some ideas. Also http://www.atari-forum.com/viewtopic.php?f=74&t=17530

There are other floppy related topics at both websites which might provide more guidance.

January 30th, 2016, 10:34 AM
Ben @ Bravo Sierra has St disk drives. I think they are over priced but might be cheaper than shipping from the UK...


Best Electronics in Canada also has them, about the same price...


Sorry I am in the UK otherwise I would mod one and send it to you...

January 30th, 2016, 10:45 AM
The Samsung SFD-321B has good OEM documentation on its jumpers and is generally pretty common (Compaq used them on lots of machines).

The single-sided drives used on the 520ST were terrible. I replaced mine with a couple of NEC 720K drives. Are you certain that pin 34 is "Disk changed" and not "Drive Ready"? My NECs have only "READY" and they worked just fine.

January 30th, 2016, 01:59 PM

Drives with no disk change generally work OK most of the time. Its only a problem if you don't re-read the directory after a disk change, and then write to the disk. A duff directory gets written and trashes the disk.

February 8th, 2016, 04:18 PM
I got an SFD-321b Rev WT-05; I did the mod seen here (http://www.atari-wiki.com/index.php/File:Samsung_SFD321B_DS0_Mod_After.jpg) but I still get the error "An error has occurred during format or copy. Target disk may be unusable." with several disks. On the new drive the bar moves slightly and I can hear it trying to format but that's the only difference. The light on the drive and ST seems to blink incessantly. Could this be the mentioned low-power issue rather than an identical problem to the original drive?

February 8th, 2016, 07:09 PM
Drives with no disk change generally work OK most of the time. Its only a problem if you don't re-read the directory after a disk change, and then write to the disk. A duff directory gets written and trashes the disk.

I dug out my copy of the Bruekmann, English and Gerits "Atari ST Internals", and indeed the 520ST floppy interface doesn't use "READY" nor "DISK CHANGE". Just the basic signals, which figures.

So what could be wrong? Well, the ST uses a WD1772 FDC, which pretty much goes directly to the drive, so no buffering. The drive and side select go through the sound chip, but they don't seem to be the problem.

The Samsung drive is a modern drive, so it draws less current than early drives. Hang a voltmeter on the +5 and see what happens to it when the drive motor switches on. Oh-be sure you're using DD and not HD disks.

February 8th, 2016, 11:32 PM
Well, this is a 1040. It looks like the mega had both those signals. I noticed activity when I inserted a disk. Perhaps I'm wrong.

But the led blinking i noted earlier after a disk is inserted, even after ejected, is quick and 'shallow' - like low intensity; it starts once you insert a disk I think and then persists. I'm thinking that now; I'm not sure if that symptom would not occur if you never inserted a disk but with the new drive I also notice a 'slow boot' to ROM, which makes me think there are read problems. My speculation is perhaps it is something like a misfiring ready light or something. I haven't fully articulated the thought but I think you might be onto something - like the drive expects ready but gets no signal or only gets a constant signal perhaps.

The disks are DD, but I probably have written over the TOS disk I wrote. So, forgetting formatting, to test read I have a few questions since I'm not sure I have a working internal floppy for my PC anymore: 1) is there a disk writing program for classic mac, or less preferably an ST emulator? 2) think windows 7 or 2000 can read ds0 floppy drives - preferably the former?

3) how can I measure the 5v? I'm not that skilled with electrical stuff. On compact macs, I would ground one lead in a port screw home and attach another to a paper clip ina particular port pin. Here I guess I would put the clip into a pin hole on the floppy cable from the board. Is there a convenient way too ground?

February 9th, 2016, 04:37 AM
Disk image writing program for classic Mac: Try diskcopy see https://support.apple.com/kb/DL1262?locale=en_US Make sure you have the PC Exchange installed.

February 9th, 2016, 06:36 AM
Wait... that's a link to Disk Copy. Are you saying Disk Copy can just read and write ST formats standard?

February 9th, 2016, 07:01 AM
The standard ST format is close enough to the PC format that disk copy should correctly write out an image. Apple doesn't list which alternate image formats it supports so you may have to try several to find one that works.

PC Exchange should manage to read and write many ST disks if you ever decide to do data transfer. Not all, some Atari ST formats don't even reliably read on the same Atari ST that wrote the disk.

There was an Mac utility that modified ST disk image headers into a form that earlier disk copy versions needed. I can't locate a copy of that. I didn't find any source for a competing classic Mac OS disk imaging program in case you hit problems with disk copy.

Now, if you move to OSX, there are many other disk imaging programs available. Some may be much better suited than disk copy.

February 9th, 2016, 08:20 AM
I have OS X but no longer with a drive.

February 9th, 2016, 12:24 PM
Is there a convenient way too ground?

On a floppy connector, the two inner pins are ground; the two outer are +5 and +12.

February 9th, 2016, 03:21 PM
Wait... that's a link to Disk Copy. Are you saying Disk Copy can just read and write ST formats standard?

"normal" ST Disks are MS-DOS standard. There is a byte set in the header that causes MSDOS to not like them. Not sure if this is a bug in MSDOS or the Atari is violating the standard if there ever was one. However many Atari folks pushed the capacity limit by writing disks with more tracks and different sector layouts which may not read at all on a PC...

February 11th, 2016, 04:43 AM

February 11th, 2016, 01:01 PM
I can confirm that that mod definitely works. You move the resistor from DC to RDY and wire the rightmost pad of RDY to pin 2; solder DS1 over to DS0 and that's it. Pretty cool.

Krebizfan: after repeated failures I was delighted to learn that you are correct. PC Exchange and Disk Copy can read .ST archives. So to that effect (I think) I was required to format on the ST first, mount the archive, and then copy the files. Even though it shows up as a "PC" disk under the exchange, I couldn't format the disks as DOS and then just copy the files. So there ideally would have to be some sort of formatting utility on Classic Mac. I assume that's what's happening on the Windows utility I used. And DiskDup+ unfortunately doesn't recognize any of these as valid disk images.

Also, on this cool archive (http://www.vintagecomputercafe.com/atari/ST/games-clean/) I notice several semi-standard image sizes - mostly 360/720k 800k and sometimes larger. I've also found files just above 720k. So far I've gotten none to actually work - an array of graphics and hardware problems, lol

February 11th, 2016, 02:20 PM
I assumed that you already knew about DS0. My bad.

February 11th, 2016, 02:44 PM
I did know about DS0... That wasn't the issue. The issue was everything prior to the semi-colon. Resoldering DS1 to DS0 doesn't work on its own. And not to be litigious, but the SFD-321B revision I got (and actually the other mods I've seen also) don't have jumpers.

February 11th, 2016, 03:28 PM
To me: jumper=piece of wire; alternatively, "strapping". That someone puts a pin header on it is immaterial. I mostly rework the SFD-321Bs to set 1.6MB mode, DS0 pin 2=DC and pin 34=ready for some Japanese PC_98 type equipment.

Sorry if you misunderstood.

February 11th, 2016, 04:04 PM
I think we're still talking past each other. This mod required moving a resistor and desoldering two pads and resoldering two other pads in addition to what you call jumpering. The "jumper" wire isn't added between pins. If you disassemble a 1040ST's internal floppy you'll note it has an actual jumper set for DS0.

February 11th, 2016, 05:36 PM
Resistor or 0-ohm shunt? When I work on the Samsungs, I just discard the 0-ohm SMTs (not really a resistor) and use a short piece of wire-wrap wire. Sometimes, I'll just use a solder bridge, if the pads are close enough together. (as in changing from DS1 to DS0).

In any case, I've probably been living with floppy drives for too long. Everything seems obvious after awhile.

Sorry for assuming too much. Maybe I should write a tutorial. Floppies aren't rocket science; they're not even little red wagon science. Dumb, dumb dumb peripherals. Even a printer is smarter.

February 11th, 2016, 07:07 PM
You should write a tutorial. This thread was supposed to be that. [That's not intended as sarcasm; I was looking for a tutorial, essentially.]