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Help IBM PS/2 model 8556 wiring 1.44MB floppy

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Reply 20 of 34, by mattw

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CharlieFoxtrot wrote on 2023-03-13, 18:36:

Yup, I meant desktop size. And yeah, I thought how the heck you have fitted a regular ATX PSU there 🤣

Actually, the wires in my case are long enough and it turned out that I can just put the whole ATX-Adapter-Board outside the PS/2 case and place desktop size ATX power next to the PS/2 case - basically it's like I have ATX connector on the back of the PS/2 instead the 100V-240V plug. I see nothing wrong in that approach as well.

Reply 22 of 34, by cbcduna

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mattw wrote on 2023-02-27, 11:36:
Finally - Success! I really cannot believe it!! the explanation is below - I am not posting pictures, because after so many expe […]
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Finally - Success! I really cannot believe it!! the explanation is below - I am not posting pictures, because after so many experiments my 34-pin regular PC floppy drive cable is an ugly mess that will confuse you and that's why I will explain in details with words only.

It was entirely brute-force approach, i.e. doing countless experiments and observe the results from them, because as you will see, when you read below what solved it - that all information online including PS2FF adapted made by June Tate-Gans that I mentioned in the few previous posts are wrong! (at least wrong for my PS/2 model 8556, which I believe is also called Model 56SX).

So, it's amazing how simple it is when you figure it out - no any resistors or circuitry is involved - hence making adapter PCB makes even less sense. What is most confusing of all is that IBM own "PS/2 3.5-inch Diskette Drives Technical Reference" document (the "ps2_fdd_trm_s42g2194_00.pdf" attached to my 1st post) is wrong - my best guess is that document is made before those models like 56, 76, etc were released and hence the information there doesn't apply for them. (I say IBM docu is wrong, because if we use the information in that docu then setting the motherboard to 1.2MB 5.25" drive made my 1.44MB 3.5" drive work - clearly that documentation cannot be right for those newer PS/2 models like 56).

Initially, when I made it work I was thinking it's a fluke and maybe it will work just with that particular regular PC 1.44MB drive I was using at the time, but luckily - it wasn't - I've already tested with 3 different regular PC 1.44MB drives - Sony, Teac and Chinon - they are all working!

Here is the minimum working configuration - one more time no resistors, no circuitry, all modifications are done on a regular PC 34-pin floppy drive cable:

1) cut pin3 and pin6 wires (see my first post pictures of those cuts and why those pins corresponding wires need to be cut). So, I cut pin3 wire after the middle connector on the cable (for considerations I explained in my first post, which are no longer relevant, but anyway - it needs to be cut - where is the best place on the cable to cut it - you decide). pin6 wire I cut close to the end of the cable that goes to the motherboard and that is the best place as it's +12V that will most likely fry your PC 1.44MB drive if it's not cut there. Nothing new here - those cuts are done for all PS/2 models when you want to mod them with regular PC 1.44MB floppy drive.

2) cut pin4 wire - again see my first post about that

3) the New finding and Critical for the Solution: cut pin9 corresponding wire - it's the wire just before the "cable twist" part of the cable starts - that's why I cut it there, i.e. after the middle connector on the cable. That pin9 is shorted to GND via the floppy drive connector - that's why it needs to be cut, because when it's shorted to GND makes 1.44MB drive not possible to work.

4) on the middle connector of you regular 34-pin floppy cable for PC, use jumper wire and short pin4 to pin5, i.e. short pin4 directly to GND (pulling it down via resistor - I used 2.2kOhms one - is not working, needs to be directly shorted to GND).

That's it - now my recently acquired IBM PS/2 is free of IBM custom parts - I removed their custom (and now dead) power supply and modded it to work with modern regular PC ATX power supply (if anyone needs guide/howto for that - let me know, it's super easy when you acquire proper parts and materials for doing the ATX mod - I did it with all off-the-shelf parts). now it's free from IBM very special floppy drive as well (dead in my case as well). In other words now it uses all standard parts - my RAM is also regular PC one that I modded to be compatible with PS/2, using this:

https://ardent-tool.com/memory/Mods_02.html

the HDD is SCSI, but standard one without any IBM "customization" and thus no changes are needed there in order to acquire cheap available replacements (if needed).

I hope the above will help other PS/2 users - as far as I can tell based on PS/2 Floppy Drive Interface Pinouts here:

https://ardent-tool.com/floppy/Pinouts.html

the solution should work with PS/2 models 56, 57, 76, 77, 90 and 95, etc, i.e. all models that have 40 or 44 pin floppy drive connector and are "media-sense" type.

Hi Matt, i have the same pc and the same problem With the use floppy 1.44mb.
I make your configuration cable but in my case can't function correct.
The floopy initialize fine but in the ps2 always say 00060400 error.
The curious is the referente disk read fine but no is posible start the machine without error 604 and the logo no ok.
Any idea?
Regards and thanks.

Reply 23 of 34, by cbcduna

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Hi,
Soon i send my data and images of my exercise.
Also, added information about the connector pannel and pinout identified with tester of connecrivity. (I do not have the case and cables, only the motherboard with FRU: 84F7994.

Reply 24 of 34, by mattw

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cbcduna wrote on 2024-01-06, 11:50:

Any idea?

unfortunately, I don't have any idea - it worked very well for me. also, as I mentioned here:

Re: Some questions about IBM PS/2 Models

you need to use the floppy only once - to make "IML"-partition, then make image of that SCSI HDD using regular PC and SCSI card (f0r backup if something happens and you need to restore) and now my IBM PS/2 is even floppy free . that way is most convenient to me as well, i.e. it is faster and easier to connect the SCSI disk to PC and copy everything I need and then put it back in the PS/2. so, the only case that really needs the floppy is to make IML-partition.

cbcduna wrote on 2024-01-06, 15:28:

only the motherboard with FRU: 84F7994.

my motherboard is the exact same FRU. so, I most definitely think you must made some mistake with modifying the cable.

Reply 25 of 34, by cbcduna

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mattw wrote on 2024-01-06, 22:22:
unfortunately, I don't have any idea - it worked very well for me. also, as I mentioned here: […]
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cbcduna wrote on 2024-01-06, 11:50:

Any idea?

unfortunately, I don't have any idea - it worked very well for me. also, as I mentioned here:

Re: Some questions about IBM PS/2 Models

you need to use the floppy only once - to make "IML"-partition, then make image of that SCSI HDD using regular PC and SCSI card (f0r backup if something happens and you need to restore) and now my IBM PS/2 is even floppy free . that way is most convenient to me as well, i.e. it is faster and easier to connect the SCSI disk to PC and copy everything I need and then put it back in the PS/2. so, the only case that really needs the floppy is to make IML-partition.

cbcduna wrote on 2024-01-06, 15:28:

only the motherboard with FRU: 84F7994.

my motherboard is the exact same FRU. so, I most definitely think you must made some mistake with modifying the cable.

Hi Matt,

send images for my cable.

Reply 26 of 34, by cbcduna

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Hi,

my understand:

- wires 3 & 6 cut
- Wire 9 cut
- wire 4 cut and short with 5 to gnd directly.

In this situation, the machine always indicate error 000604000 and the logo no OK in screen. However, the disk of reference load without problem.

But when i want start the pc with the OS floppy in drive can't read.

Regards

Reply 27 of 34, by cbcduna

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Hi,

the wire 17 is cut for identified the type of floppy inserted (2.0 Mb) in media type ID1 (pin17)

but the result is same cut or not for the error 604.

Send another image with perspective.

Reply 28 of 34, by cbcduna

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Hi,

add image for error 604 in screen.

In this situation, any action to load from floppy the OS not function. The drive try to read but no load.

The only option to load OS is boot with the Reference disk and choice the option "Load Operation System" in menu. With the restart and with the OS floppy inside the system load corectly and success A>....

In my case only have a SCSI disk of 2GB. and for imndicate in your linkabout SCSI, in 56sx system not is possible use disk with this capacity. Its OK?

Regards.

Reply 29 of 34, by mattw

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@cbcduna:

do I understand right - you can boot the "Reference Diskette", but you cannot boot DOS from the floppy? so, maybe, everything is alright, I mean I doubt that I ever tried to boot DOS from the floppy. And after all the whole point is to be able to boot the "Reference Diskette", then after I explain you use it to create the IML partition on your SCSI drive :

Re: Some questions about IBM PS/2 Models

and after that I've never ever even wanted to use a floppy on that PS/2.

unfortunately, that PS/2 is limited to maximum 1GB SCSI drive:

https://ardent-tool.com/IBM_SCSI/SCSI_over_1GB.html

on mine I am using 500GB SCSI drive that I took from an old PowerMac 7300 that I bought for next to nothing, because it was with totally broken case. I mean buying separate old SCSI disk now is sold on speculative prices, but those old PowerMac machines have usually 500MB or 1GB SCSI drive, which are ideal for such PS/2.

Reply 30 of 34, by cbcduna

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Hi Matt,
Thanks for the information.
My idea will be to eliminate the error missage to boot about media sense of drive.
I search a Hard disk scsi minor to 1gb. For créate the IML partition.

Regards and thanks for all

Reply 31 of 34, by cbcduna

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Hi,

news:

making diferents tests with of signals pins 2,4, 9, 17, 27 and 33.

The result for Floppy 3,5 1.44Mb the correct status is Pin2=0, PIN4=0, PIN9=0, PIN17=1, PIN27=0 and PIN33=0. With this disposition the function is correctly and the driva load reference Disk and SO fine.

With this information, the file of specification Floppys to IBM in my case is correct all configurations for 1.44mb drives in tables. (PIN 4 and PIN 9 must be to 0 for Drive type ID1 and ID0 )

Reply 32 of 34, by mattw

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cbcduna wrote on 2024-01-10, 20:28:

The result for Floppy 3,5 1.44Mb the correct status is Pin2=0, PIN4=0, PIN9=0, PIN17=1, PIN27=0 and PIN33=0. With this disposition the function is correctly and the driva load reference Disk and SO fine.

I am glad to hear, you found a solution that works (in you case), but are you saying with my way of wiring the cable, you were not even able to load the Reference Diskette (and not just DOS from a floppy disk)? I cannot believe this, I mean there has to be some difference (maybe ROM version) between mine and your 8556 mainboard.

Reply 33 of 34, by cbcduna

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Hi Matt,

With your way of wiring the unit also works, but it detects it as a 2.88 Mb unit and not as a 1.44 Mb unit.

The reference floppy disk loads equally because the 2.88 drive can also read 1.44 Mb floppy disks, but the system in bios reports a 2.88 drive even though it is 1.44 Mb.

Regards.

Reply 34 of 34, by mattw

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cbcduna wrote on 2024-02-13, 18:45:

With your way of wiring the unit also works, but it detects it as a 2.88 Mb unit and not as a 1.44 Mb unit.

thanks, in any way, it's good we got to the bottom of it.