• Please review our updated Terms and Rules here

A tale of two 386s, a 3.5" floppy drive, and woe.

bozimmerman

Experienced Member
Joined
May 26, 2005
Messages
52
Location
Austin, Texas
Hello all,

I'm not an expert on olde PCs, so please bear with me.

I have two old 386s.

One works fine, has a couple of floppy drives, and a hard drive, and it's happy, but it's a 386sx, so its best isn't great.

The other is a 386dx with a math coprocessor and a tower case. So cool! It too has a hard drive and boots fine from it.

But to save my freaking flipping no good life I can not get this darned thing to read a floppy disk.

I gave up on the onboard floppy controller awhile ago. "Drive seek error on 1" at boot and no recognition at all from DOS.

However, since then I've tried IO/cards of various shapes and sizes, SCSI cards with floppy controllers, and even a sound card or two. But in all of those cases, after booting to DOS from the hard drive, it simply can not read the disk in the drive. Trying to pull a directory gets me lots of spinning action and eventual failure.

Before you ask, I know the 3.5" HD floppy drive works. I've tested it in the 386sx I mentioned before. In fact, whenever I feel suspicious, I test it again. And it is still fine in there.

Is there some floppy controller magic I need to understand?

If it matters, the 386sx is a Commodore PC50-II, and the troublesome 386dx is a Commodore PC60-III.

Thanks for any advice. I mess with this computer at least once a year, cry a lot, and then put it away. I'd sure like some resolution.

- Bo
 
Last edited:
Hi Bo,

Well, you're better off than some 386 owners--Commodore actually published the schematic for the PC60-III here:

https://computerarchive.org/files/c...II_System_Schematics_314676-01_(1990_Jan).pdf

Looking at it-and in particular, page 15 of 20 in the schematic, I see that the FDC is a WD37C65B and it appears that it's hard-wired to port 03fx, IRQ 6 and DMA 2. So sticking a regular ISA floppy controller is going to create conflicts and not work. So, you're going to have to work with what's on the motherboard.

You'll want to check the state of motherboard jumpers J37, J30 and J43 (although that should be hard-wired).

Is U127 socketed?

Finally, what electronics tools (logic probe, oscilloscope, DMM, etc.) do you have at your disposal?
 
Thanks for your reply Mr. Chuck,

J37 is a 2-pin jumper and it's open
J43 is a 3-ping jumper and it's completely open
J30 *I think* is the little two-pin jumper between two groups of 4 square chips. And it's open too.

U127 is socketed, but only because I socketed. My first thought was a bad controller chip, and those WD37C65Bs are common as hell, so I clipped out the old one, but in a socket, and dropped a brand new one in. Didn't change a damn thing.

I have several multi-meters of varying quality, and a little hand-held electric oscilloscope (which, despite my electronical ignorance, came in handy once when I determined that a +2.5v output on a power supply was actually a 5V clock).

Thanks for your response. I hope this information inspires another!

- Bo
 
Oh, since the computer model was useful, I might as well mention the floppy drive as well -- it's an ALPS DF354HO68F. When I first received the computer, it had a CHINON-357, but that little mother-father doesn't even work right in the 386SX, so I figure it's dead and keep it around only for nostalgia.
 
I had this happen to me with an Everex. It did allow me to disable the onboard FDD controller but after a while it died anyway. Something must have fried on the MOBO. My suggestion: find a generic 80386DX if you really want one. Those are still pretty common and cheap. Part out the Commodore.
 
If you don't have the tools and experience, maybe an IDE based floptical type drive would work for you. Something like the Imation LS‑120 SuperDisk, if it would work in a 386DX system. If not, a Zip drive would be an idea.
 
I had this happen to me with an Everex. It did allow me to disable the onboard FDD controller but after a while it died anyway. Something must have fried on the MOBO. My suggestion: find a generic 80386DX if you really want one. Those are still pretty common and cheap. Part out the Commodore.

Hahahahahahahahahaha. Not gonna happen.

Please allow me to introduce myself.

http://gallery.zimmers.net

- Bo
 
If you don't have the tools and experience, maybe an IDE based floptical type drive would work for you. Something like the Imation LS‑120 SuperDisk, if it would work in a 386DX system. If not, a Zip drive would be an idea.

LS-120s will work on something that old, but you need a device driver for them on mainboards that don't natively support them. Which means, to my knowledge, any 386, and MOST 486 boards will need the drivers. Anything beyond that up to any modern board that has pata, or a pata-sata adapter, will use them functionally without help.
 
Hmmm....

Looking at the schematic, it appears that the PC60 doesn't use the usual IBM drive cabling (i.e. one with a "twist"), but a "flat" one with drive select jumpers set to 0-3 for each of 4 drives (yes, your 386 has support for 4, count 'em 4, internal floppy drives).

So that 3.5" floppy drive has to use a "flat" cable and be set to DS0 (PC floppy drives are set to DS1) in order to work as drive A:. The second floppy would be set to DS1 and use the same "flat" cable.

To summarize, there's probably nothing at all wrong with your PC60. Just with your cabling and drive jumpering.
 
I was going to ask the probably obvious, but do you have 4 drives in it right now?
pc60-iii.gif
Is there a BIOS to disable the onboard floppy? You have the other drives working or unplugged? I *think* I've seen BIOS bugs that make disabling onboard not work on some other systems but that doesn't offer any solution other than a BIOS update if there were any. I was wondering if it supports HD or if it's limited to DD drives perhaps? I think I only have a Colt so nothing real to compare it to feature wise, although you said it does work in your PC50 so that'd imply the 60 would probably also support it.

Oh.. welcome back also btw :) Great to see you active. I was starting to worry when I saw the collections for sale in RR on craigslist.
 
I was going to ask the probably obvious, but do you have 4 drives in it right now?
pc60-iii.gif
Is there a BIOS to disable the onboard floppy? You have the other drives working or unplugged? I *think* I've seen BIOS bugs that make disabling onboard not work on some other systems but that doesn't offer any solution other than a BIOS update if there were any. I was wondering if it supports HD or if it's limited to DD drives perhaps? I think I only have a Colt so nothing real to compare it to feature wise, although you said it does work in your PC50 so that'd imply the 60 would probably also support it.

Oh.. welcome back also btw :) Great to see you active. I was starting to worry when I saw the collections for sale in RR on craigslist.

So funny you should post that picture! If memory serves, that picture came from the auction where I picked it up.

Anyway, the unit did NOT come with four drives, only two. However, it did come with a spare motherboard (!!), but that one doesn't post at all, so I've always been focusing on the one that does. The BIOS does not let you turn off the internal controller the way modern ones do. It does allow me to select "NONE" for all four positions, but that's not the same thing I guess. Besides NONE, the BIOS offers options for 720k and 1.4m 3.5" drives, and 360k or 1.2m 5.25" drives.

If you could PM me the information about the local collections for sale, I'd be curious. It certainly wasn't me.

- Bo
 
Hmmm....

Looking at the schematic, it appears that the PC60 doesn't use the usual IBM drive cabling (i.e. one with a "twist"), but a "flat" one with drive select jumpers set to 0-3 for each of 4 drives (yes, your 386 has support for 4, count 'em 4, internal floppy drives).

So that 3.5" floppy drive has to use a "flat" cable and be set to DS0 (PC floppy drives are set to DS1) in order to work as drive A:. The second floppy would be set to DS1 and use the same "flat" cable.

To summarize, there's probably nothing at all wrong with your PC60. Just with your cabling and drive jumpering.

Hello Mr. Chuck,

Well, I did find a flat cable with 2 edge connectors, which I tried with the 5.25", alternately telling the BIOS that it was drive 1 or 2. I also found a single jumper on this drive and tried closing both of its positions. But all I get is Drive Seek Error on 1 (or 2).

I don't have a 3.5" fully flat cable, but tried using the "first position/closest to the board" connector on a 2-drive-connector twisted cable, since that appeared flat enough going to the board, and again tried all possibilities in the BIOS -- always the same "Drive Seek Error on 1" (or 2). This particular floppy had no obvious jumpers.

At one point in my yearly ventures, I took a stab at documenting every jumper on the board, and had written nothing I understood for the jumpers you mentioned. J37 I had as DRV-22, J43 as RWC-36 FMODE, and for J30 PCVAL-24. Would any of those be capable of disabling the onboard controller enough to allow a multi-IO card to take over those functions? If so, I think I'd rather do that. Heck, that goes for the IDE controller as well -- perhaps I can even upgrade it.

Once again, my most sincere thanks for any response,
Bo Zimmerman
 
We have had a discussion on another Commodore recently, the Colt aka PC10-III/PC20-III: http://www.vintage-computer.com/vcf...61-few-quick-question-on-Commodore-Colt/page2
Conclusion is that it doesn't use the regular IBM cabling either, and an untwisted cable, and a floppy drive jumpered to have 'motor on drive select' seems to be the way to success. Chances are your PC60-III works the same way.

Hello Scali,

It's so curious that the same drives work fine in the PC50-II, ostensibly an earlier 386 model from the same company. The PC10/20s were 8088 based, and presumably more than a few years older.

Either way, my question for you is this: Are there particular make/model of floppy disk drives I should be focusing on here? I keep hearing about these PC floppy drives with jumpers to do this and jumpers to do that. But that seems to presume both a year-range of models, and the availability of documentation to know 1. where to find these jumpers, and 2. which one is which. So if you have recommendations, I am all ears sir.

As it is, I'll start poking around for more flat floppy cabling.

- Bo
 
The problem is that almost all later 3.5" drives have the drive select hard-wired--that is, not changeable. Earlier ones often had drive-select jumpers. Unfortunately, the model number is not a good guide. I recently reworked a Citizen drive identical in number, type, etc. with a slightly older one. The older one had drvie-select jumpers under the cover; the newer one, no such luck. It took unsoldering and moving two very small SMD jumpers and two SMD resistors. Not quite the same thing.

That being said, of modern 3.5" drives, I find the Samsung SFD-321B the easiest to reconfigure (you'll still need a soldering iron, but it's not difficult) and they're pretty easy to find.
 
The problem is that almost all later 3.5" drives have the drive select hard-wired--that is, not changeable. Earlier ones often had drive-select jumpers. Unfortunately, the model number is not a good guide. I recently reworked a Citizen drive identical in number, type, etc. with a slightly older one. The older one had drvie-select jumpers under the cover; the newer one, no such luck. It took unsoldering and moving two very small SMD jumpers and two SMD resistors. Not quite the same thing.

That being said, of modern 3.5" drives, I find the Samsung SFD-321B the easiest to reconfigure (you'll still need a soldering iron, but it's not difficult) and they're pretty easy to find.

Thanks, I'll pick one up immediately.

So.. no chance of disabling the onboard controller enough to let a Multi-IO board controller work? Shame. I'm not optimistic. If the onboard controller was capable of making the drives spin, or make a noise, or turn on their activity light, or do ANYTHING other than give that stupid POST error, I would be more with you.

Well, I've been taking a crash course in floppy controller pinouts, perusing those schematics, cross referencing with the controller chip docs I found online. The only thing I can think to do right now is check the cable header pins to make sure they match what the schematic says, and then start looking for docs on the various 3.5" floppy drives I have, at least until the SFD arrives.

- Bo
 
Last edited:
Is the WD37C65B the DIP version or the PLCC one? If the PLCC one, I have a tube of the things, NOS. If it's in a PLCC socket, so much the better. I can probably also give you a few DEBUG commands to try to see that it's working.
 
Is the WD37C65B the DIP version or the PLCC one? If the PLCC one, I have a tube of the things, NOS. If it's in a PLCC socket, so much the better. I can probably also give you a few DEBUG commands to try to see that it's working.

Thanks, but it's the DIP version WD37C65C (not "B" -- schematic searches didn't show a diff), and I think I have a even have another spare from back when I socketed it.

I tried running without the chip altogether just to see if the computer would post, and it does. Heck, even the error message was the same... those BIOS programmers aren't very original or specific in their messages I guess. However, even with the FDC chip removed, the Multi-IO card worked no better than before, so whatever is causing the Multi-IO board to have its own problems, it's not that chip.

Next I spot checked a few of the pins that run directly from the FDC chip to the floppy header pins (like DS0 for example), and they seem fine.

BTW, since there's a missing pin "3" on the motherboard, I assume this is a "SHUGART" interface, whatever that means?

I also tried a spare Amiga HD 3.5" drive I kept around for my Amiga 4kt, and saw no difference in behavior -- using my floppy cable that has a 3.5" connector BEFORE the twist, of course.

- Bo
 
Hello Scali,

It's so curious that the same drives work fine in the PC50-II, ostensibly an earlier 386 model from the same company. The PC10/20s were 8088 based, and presumably more than a few years older.

8088s have been around for a long time... The Colt/PC10-III/PC20-III date from around 1988.
I think the 'II' and 'III' were a generation, so likely the PC60-III is from around the same time.
I know later models went to a more Amiga-style case, which was around 1990. I had a 386SX-16 like that.

Either way, my question for you is this: Are there particular make/model of floppy disk drives I should be focusing on here? I keep hearing about these PC floppy drives with jumpers to do this and jumpers to do that.

Yes, Commodore liked to use Chinon drives. And you'd want them from around that era, so pre-1990 probably (I believe the FZ-354 or FZ-357 are models to look for).
I know someone posted a list of floppy drives and their jumpers somewhere recently, but I can't find the post atm.
 
I received the SFD-321B. Of course, as-is, the onboard controller ignores it, like it ignores all floppy drives. I did manage to carefully remove the casing and I can see all the tiny jumper pads. I have no idea what I'm supposed to do from here. Not even a guess.

So, On Scali's recommendation, I tried some of my Chinon mechanisms -- I have several kinds as spares for the Amigas, and he is correct -- the 3.5" drive the computer came with was a Chinon. Anyway, "Seek error on Drive 1", as always, so no luck there.

I also fiddled around with more BIOS settings -- disabling all caching, disabling the onboard LPT, COM, and BUS MOUSE ports, just because I could. I dropped the bus speed down to 8mhz, just for fun. I suppose I should mention that the CMOS batteries were dead as doornails when I got this thing, so I've never been comfortable knowing what the correct value for that one is.

Are there any floppy pins that can be snooped upon with my multi-tester to some benefit?

Lastly, as usual, I played around with the Multi-IO board. It can see the drives just fine -- it gives them their little kick, and when the computer says "go", they read the disk. I can hear it passing tracks for about 5 seconds, then it just stops. No "Starting MS-DOS" (the disk is one of my trusty DOS 6 boots), nothing. I can even hit F1 again, and it will again read tracks for several seconds, and stop again. Very strange.

Anyway, I guess the last thing to try will be the flat cables when they arrive. If that doesn't work, well, I've given this computer it's yearly attention. I dearly want to be able to use it, but it's taking up half my worktable space, and I have other projects behind it I can make some progress upon -- including some Commodore external IEEE-488 hard drives I picked up that I'll be cleaning up, testing, reading the ROMs out of, etc ... if anyone cares for such things.

- Bo
 
Back
Top