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IBM PS/2 Floppy converter development

S

steve314

Member
Joined
Jan 12, 2019
Messages
41
Location
Fredericton, New Brunswick, Canada
Hi all,

A few months ago I purchased an IBM PS/2 model 50 for $20 CAD. The floppy drive didn't work, so I've been developing a PCB to connect a standard floppy drive to the computer. At the moment, it consists of an edge connector and floppy connector, as well as some pullup resistors and a power connector(output for the floppy drive, so I don't have to modify the power supply).

It kind of works - when the computer boots, the floppy head moves back and forth, just like on the original drive. However, I get a floppy error and the system refuses to boot. Doing some research, I found one or two people saying that a floppy drive with jumpers is required. This is to change the logic level between CMOS and TTL(I'm not sure which one is the correct one for the PS/2 systems). Since the header requirement is rarely mentioned, I have a feeling a lot of drives work with both logic levels by default(but clearly mine don't!)

If anyone has a floppy drive with headers they are willing to give away(or maybe sell), that would be great. I need to confirm the board works before I start designing a revision with logic level shifting built in. Eventually, I would like to sell the boards alongside a 3D printed floppy drive mount. (I am also designing an MCA card, but that's another project entirely.)

I am also interested if anyone knows more about this. I was unable to find very much information on the specifics.
 
AFAIK, all SA400 floppy drives, no matter their technology work on TTL levels. Signaling is done via open-collector (or in the case of CMOS, open-drain). Since it's OC signalling, some sort of pull-up termination is usually required.

You might want to have a look at this chestnut from 2013 Adapting a cheap 1.44M drive to a Model 50

Sadly, I can't find a mirror for the charter.net page--maybe there's one out there. Sigh. The old problem of writing our web content in sand... :(
 
Chuck(G) said:
AFAIK, all SA400 floppy drives, no matter their technology work on TTL levels. Signaling is done via open-collector (or in the case of CMOS, open-drain). Since it's OC signalling, some sort of pull-up termination is usually required.

You might want to have a look at this chestnut from 2013 Adapting a cheap 1.44M drive to a Model 50

Sadly, I can't find a mirror for the charter.net page--maybe there's one out there. Sigh. The old problem of writing our web content in sand... :(
Click to expand...

Yeah, I've seen that video along with other posts mentioning the same thing. I already have those pullup resistors included - they're the ones I mentioned in my post.
 
eeguru said:
I'm assuming you've seen these:

https://www.ebay.com/itm/IBM-72X675...5:g:hegAAOSwzahZib~z:rk:1:pf:1&frcectupt=true
Click to expand...

I think that's actually for the External floppy drive option. The MCA card just gives you the external port to hook up the drive, and then you use that connector to connect the card to the Drive B slot in the Floppy Riser inside the system. You can see it originally came together as a kit in this listing:

https://www.ebay.com/itm/IBM-645024...1:g:9c8AAOSwzXBZib~g:rk:5:pf:1&frcectupt=true

Now if it will work for any floppy drive though I don't know. At the very least I'd imagine you're still going to be missing the power pins.
 
Chuck(G) said:
AFAIK, all SA400 floppy drives, no matter their technology work on TTL levels. Signaling is done via open-collector (or in the case of CMOS, open-drain). Since it's OC signalling, some sort of pull-up termination is usually required.

You might want to have a look at this chestnut from 2013 Adapting a cheap 1.44M drive to a Model 50

Sadly, I can't find a mirror for the charter.net page--maybe there's one out there. Sigh. The old problem of writing our web content in sand... :(
Click to expand...

Chuck,
I know from past experience with external ATARI drives that in 5.25" drives all are not equal and the Atari ST will not work with some, usually older 5.25" drives. So perhaps not CMOS but LS TTL or something that requires a lower drive level
Dave
 
I've repaired all but one (it had mechanical damage) PS/2 floppy drives of different brands and types (small button, large button, HD, DD) just by replacing the electrolytic capacitors on the motor control board (bottom part of the drive). Swollen caps causing spindle motor to lost speed feedback and run fast. Head misalignment is rarely an issue on this drives (only one drive needed it in all my PS/2 computers) and even it has, it can be easily aligned by using ImageDisk software with adequate accuracy.

Adapting a modern drive is electrically not that hard but mechanical adaptation is challenging particularly for big-button, thick drives. With that adapter with pull-ups, I've successfully tested modern Teac, Alps, Mitsumi, Samsung and Sony branded floppies in different PS/2 computers.

steve314 said:
Hi all,

A few months ago I purchased an IBM PS/2 model 50 for $20 CAD. The floppy drive didn't work, so I've been developing a PCB to connect a standard floppy drive to the computer. At the moment, it consists of an edge connector and floppy connector, as well as some pullup resistors and a power connector(output for the floppy drive, so I don't have to modify the power supply).

It kind of works - when the computer boots, the floppy head moves back and forth, just like on the original drive. However, I get a floppy error and the system refuses to boot. Doing some research, I found one or two people saying that a floppy drive with jumpers is required. This is to change the logic level between CMOS and TTL(I'm not sure which one is the correct one for the PS/2 systems). Since the header requirement is rarely mentioned, I have a feeling a lot of drives work with both logic levels by default(but clearly mine don't!)

If anyone has a floppy drive with headers they are willing to give away(or maybe sell), that would be great. I need to confirm the board works before I start designing a revision with logic level shifting built in. Eventually, I would like to sell the boards alongside a 3D printed floppy drive mount. (I am also designing an MCA card, but that's another project entirely.)

I am also interested if anyone knows more about this. I was unable to find very much information on the specifics.
Click to expand...
 
steve314 said:
I've seen all of those before, unfortunately. This link: http://webpages.charter.net/zip4dos/PS2 may be helpful but I have been unable to find a mirror anywhere.
Click to expand...
I have a copy of that URL. Which files do you need?
Code: 
-rw-r--r-- 1 root root   38377 Dec 29  2013 badpage.JPG
-rw-r--r-- 1 root root  293197 Dec 29  2013 blowup.jpg
-rw-r--r-- 1 root root   94457 Dec 29  2013 Fdpinout1.jpg
-rw-r--r-- 1 root root    1866 Jan 25  2016 index.html
-rw-r--r-- 1 root root     935 Dec 29  2013 Narration.txt
-rw-r--r-- 1 root root    2000 Dec 29  2013 Notes.txt
-rw-r--r-- 1 root root 2146042 Dec 29  2013 test1.jpg
 
Tor, perhaps one of the forum members would like to re-post the information on their own web servers. I see the charter.net site referenced on several other pages.
 
Yes, that would be good. I have a copy of http://webpages.charter.net/zip4dos (copied Jan. 2016) but I can't provide a mirror myself. Anyone wanting to put that on their mirror, please PM me. It's only about 9.6MB.
I don't have the rest of the charter.net site, only the zip4dos part.
 
pcdata76 said:
I've repaired all but one (it had mechanical damage) PS/2 floppy drives of different brands and types (small button, large button, HD, DD) just by replacing the electrolytic capacitors on the motor control board (bottom part of the drive). Swollen caps causing spindle motor to lost speed feedback and run fast. Head misalignment is rarely an issue on this drives (only one drive needed it in all my PS/2 computers) and even it has, it can be easily aligned by using ImageDisk software with adequate accuracy.

Adapting a modern drive is electrically not that hard but mechanical adaptation is challenging particularly for big-button, thick drives. With that adapter with pull-ups, I've successfully tested modern Teac, Alps, Mitsumi, Samsung and Sony branded floppies in different PS/2 computers.
Click to expand...

My multimeter has a capacitance setting. I already went through all the caps on the board and they're reporting the right capacitance.

Hardware modification isn't an issue; I can just design and 3D print what I need.
 
UPDATE!

I noticed the floppy drive motor was spinning when the head wasn't moving, and the motor wasn't spinning when the head was moving. Thinking the motor enable signal may have been inverted, I used a piece of tape to isolate the motor pin. I then scraped a piece off the PCB I designed(NOT the PS/2, I would never hurt it like that) and shorted it to ground. Because of this, the floppy motor would spin always, as long was the machine was turned on.

It worked! The system actually booted. Now, I have to figure out why my signal is inverted but nobody else has had that problem. But I'm making progress!!
 
steve314 said:
Hi all,

A few months ago I purchased an IBM PS/2 model 50 for $20 CAD. The floppy drive didn't work, so I've been developing a PCB to connect a standard floppy drive to the computer. At the moment, it consists of an edge connector and floppy connector, as well as some pullup resistors and a power connector(output for the floppy drive, so I don't have to modify the power supply).

It kind of works - when the computer boots, the floppy head moves back and forth, just like on the original drive. However, I get a floppy error and the system refuses to boot. Doing some research, I found one or two people saying that a floppy drive with jumpers is required. This is to change the logic level between CMOS and TTL(I'm not sure which one is the correct one for the PS/2 systems). Since the header requirement is rarely mentioned, I have a feeling a lot of drives work with both logic levels by default(but clearly mine don't!)

If anyone has a floppy drive with headers they are willing to give away(or maybe sell), that would be great. I need to confirm the board works before I start designing a revision with logic level shifting built in. Eventually, I would like to sell the boards alongside a 3D printed floppy drive mount. (I am also designing an MCA card, but that's another project entirely.)

I am also interested if anyone knows more about this. I was unable to find very much information on the specifics.
Click to expand...
IIRC Texelec offers an adapter.
texelec.com

IBM PS/2 to Standard Floppy Adapter - TexElec

Has your old IBM PS/2 ‘planar’ floppy drive stopped functioning? Would you like to use a standard floppy drive, or better yet, a Gotek or HxC floppy emulator? If so, then we have the solution for you! This adapter will allow you to connect a standard 3.5″ floppy drive to your PS/2. Some PS/2...
texelec.com texelec.com
 
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