Read all relevant information about your system and parts in the ardent tool. Here is the main page for 55SX and it probably already answers many questions and introduces you to the wonderful and annoying world of IBM PS/2s:
https://www.ardent-tool.com/8555/Planar.html/

Learn the system, it helps you long way with these proprietary thingies.

So first question about the MCA Bus. I want to switch the internal HDD for a MCA SCSI 50 pin card and connect a SD2SCSI solution.
What is the max size of HDD space i can use?p
Do i need IBM driver for the scsi board when im running DOS?

Instead of hunting an SCSI controller, IDE controller is probably better option. Here is a new one and easily available:
https://zzxio.com/product/mcide/
Many MCA parts are unobtanium or extremely pricey. I can't say about the maximum size of HDD, it depends on the bios, but that IDE controller has XTIDE so it doesn't matter.
About drivers generally, you always at least need a setup floppy for the MCA card you are installing. It might be a hassle to track that down for some vintage cards.

Next question is about the CPU.
I know its a slow 386 SX with 16MHz. Is it possible to switch the cpu? I mean desolder and socket another one, for example a 386DX 33?

Just soldering a new CPU doesn't solve anything, and slapping a DX processor on a socket of SX with 16 bit bus isn't possible in any case. Ardent tool page has information about possible CPU upgrades. It is best to take these old system as is and enjoy what they offer. 386SX+VGA is a great system for late 80s and early 90s gaming and 386 still gives you good memory management compared to a similar speed 286.

Is there a midi board for MCA?

Most likely, but good luck finding one or not needing to trade your kidney for it. Most affordable sound upgrade is probably this new SB clone:
https://texelec.com/product/resound-new-wave-mca/

Couple of other things you need to know:
You need a working floppy drive. Period, it is a must. If and when your CMOS battery dies or you make changes to your system, such as add memory, you need to use setup floppy to make changes to the CMOS as there is no "normal" bios setup screen. If battery runs out and you can't use setup floppy, you can't boot the system. Unfortunately drives on these are extremely unreliable. Common issues are bad and leaking SMD caps, so recapping is almost always required and people were recapping these already in the late 90s. I had to also recap the drive on my 35SX. You also can't use standard floppy with these systems. Generally IBM PS/2 floppy drives are physically in two categories: ones with edge connector and ones with a regular looking 34pin cable, except that 34pin cable also carries power so the drives and controllers are not standard. Another group is non-media sensing and media sensing drives. Gladly, you can get both type of adapters nowadays from ebay from a Canadian company, I think. PS/2s had also drives with different capacities, you have most likely 1.44MB and it may support some 2.88MB drives. If your floppy drive doesn't work, you don't want to try to fix it and you need to use regular drive with an adapter, be prepared that the eject button of standard drive doesn't fit with the front panel. But at least you have a working floppy drive.

For RAM, you can't use standard FPM sticks. PS/2s require parity memory, but of course standard parity won't work on these systems. Some standard memory can be modified to work with PS/s and there is more information about that in ardent tool. It is your first source of information pretty much always. There is also good information here in vogons about solving many issues and repairing these things as countless of other people have pulled their hair out while trying to get these to a working condition or expanding them and not able to use anything standard with them.

If you are searching original parts for the system, refer to IBM documentation in ardent tool and see what is compatible with your system. If some part FRU number isn't listed as compatible with your system and you can't find confirmation from anywhere else, it is safest to assume that the part is not compatible with your computer. First, it may save you money and second it may save your system. For example, plug a wrong type of floppy drive to your system and you may fry the onboard floppy controller.

Good luck, these are awesome systems!

CharlieFoxtrot wrote on 2023-09-06, 16:09:

Read all relevant information about your system and parts in the ardent tool. Here is the main page for 55SX and it probably alr […]
Show full quote

Read all relevant information about your system and parts in the ardent tool. Here is the main page for 55SX and it probably already answers many questions and introduces you to the wonderful and annoying world of IBM PS/2s:
https://zzxio.com/product/mcide/

Learn the system, it helps you long way with these proprietary thingies.

So first question about the MCA Bus. I want to switch the internal HDD for a MCA SCSI 50 pin card and connect a SD2SCSI solution.
What is the max size of HDD space i can use?p
Do i need IBM driver for the scsi board when im running DOS?

Instead of hunting an SCSI controller, IDE controller is probably better option. Here is a new one and easily available:
https://zzxio.com/product/mcide/
Many MCA parts are unobtanium or extremely pricey. I can't say about the maximum size of HDD, it depends on the bios, but that IDE controller has XTIDE so it doesn't matter.
About drivers generally, you always at least need a setup floppy for the MCA card you are installing. It might be a hassle to track that down for some vintage cards.

Next question is about the CPU.
I know its a slow 386 SX with 16MHz. Is it possible to switch the cpu? I mean desolder and socket another one, for example a 386DX 33?

Just soldering a new CPU doesn't solve anything, and slapping a DX processor on a socket of SX with 16 bit bus isn't possible in any case. Ardent tool page has information about possible CPU upgrades. It is best to take these old system as is and enjoy what they offer. 386SX+VGA is a great system for late 80s and early 90s gaming and 386 still gives you good memory management compared to a similar speed 286.

Is there a midi board for MCA?

Most likely, but good luck finding one or not needing to trade your kidney for it. Most affordable sound upgrade is probably this new SB clone:
https://texelec.com/product/resound-new-wave-mca/

Couple of other things you need to know:
You need a working floppy drive. Period, it is a must. If and when your CMOS battery dies or you make changes to your system, such as add memory, you need to use setup floppy to make changes to the CMOS as there is no "normal" bios setup screen. If battery runs out and you can't use setup floppy, you can't boot the system. Unfortunately drives on these are extremely unreliable. Common issues are bad and leaking SMD caps, so recapping is almost always required and people were recapping these already in the late 90s. I had to also recap the drive on my 35SX. You also can't use standard floppy with these systems. Generally IBM PS/2 floppy drives are physically in two categories: ones with edge connector and ones with a regular looking 34pin cable, except that 34pin cable also carries power so the drives and controllers are not standard. Another group is non-media sensing and media sensing drives. Gladly, you can get both type of adapters nowadays from ebay from a Canadian company, I think. PS/2s had also drives with different capacities, you have most likely 1.44MB and it may support some 2.88MB drives. If your floppy drive doesn't work, you don't want to try to fix it and you need to use regular drive with an adapter, be prepared that the eject button of standard drive doesn't fit with the front panel. But at least you have a working floppy drive.

For RAM, you can't use standard FPM sticks. PS/2s require parity memory, but of course standard parity won't work on these systems. Some standard memory can be modified to work with PS/s and there is more information about that in ardent tool. It is your first source of information pretty much always. There is also good information here in vogons about solving many issues and repairing these things as countless of other people have pulled their hair out while trying to get these to a working condition or expanding them and not able to use anything standard with them.

If you are searching original parts for the system, refer to IBM documentation in ardent tool and see what is compatible with your system. If some part FRU number isn't listed as compatible with your system and you can't find confirmation from anywhere else, it is safest to assume that the part is not compatible with your computer. First, it may save you money and second it may save your system. For example, plug a wrong type of floppy drive to your system and you may fry the onboard floppy controller.

Good luck, these are awesome systems!

I don't have a PS/2 but this was a very interesting read 😁 👍

welcome! The magical world of IBM PS/2 is both challenging and occasionally rewarding. I love these systems, but they can be a ROYAL pain in the ass. They were never popular, and were practically non-existent outside of the corporate sector. So gaming on these systems is challenging at best. So if this is your first retro computer, its going to be a wild ride.

"So first question about the MCA Bus. I want to switch the internal HDD for a MCA SCSI 50 pin card and connect a SD2SCSI solution. "
You can do that! The special snowflake drives are utter garbage. Butt.... I would not recommend SCSI unless you already have the hardware. I would however, recommend this new card: https://zzxio.com/product/mcide/ I want to get one, but I'm spending money on other things at the moment. IBM mca SCSI cards are rather common, but not as cheap as their ISA/PCI counterparts. Also some use special cables.

"What is the max size of HDD space i can use? Do i need IBM driver for the scsi board when im running DOS? "

normally SCSI does not suffer from size issues. normally. this is IBM. This will depend on what SCSI card you end up getting. but generally speaking, the top end is 500mb/1gb. - as for drivers, none are needed for dos or windows. now if you are installing a CD or other removable media then typical drivers are needed. but nothing special compared to "normal" scsi systems. You will get intimately familiar with the setup disk and ADF files. ^.^

"I know its a slow 386 SX with 16MHz. Is it possible to switch the cpu? I mean desolder and socket another one, for example a 386DX 33?"

physically... yes. practically? not a snowballs chance in hell, unless you are already highly skilled in electronics. And there is even less of a chance of overclocking. The platform is just not built for it.

Cpu upgrades exist. they are unique to each ibm machine (get used to that). here is an image: http://john.ccac.rwth-aachen.de:8000/alf/ps2_ … 50z_4_full.jpeg Be prepared to throw your wallet at the screen, because they dont come up often, and when they do...

"Is there a midi board for MCA? "

https://www.ebay.com/sch/i.html?_from=R40&_tr … pu+imc&_sacat=0

These are pretty rare. as the last time I saw them on ebay was like 5 years ago.

"Its my first PS/2 so sorry for my questions."
dont be! you dont learn unless you ask. I think someone else mentioned the ardent tool: https://ardent-tool.com/ it is the defacto standard for all PS/2 Info. 95% of your questions can be answered there. Also there are some facebook groubs, but fuck facebook. Also there is a slow movement of topics at: https://groups.google.com/g/comp.sys.ibm.ps2.hardware

Many thanks guys! Sound like there is a lot of work to do. But also fun for me.
My 55SX has a bad cmos battery. But it also include the Setup floppy. Still waiting to get the package.
Also good to know that i have to recap board and drive. I think than PSU also..
I did many retro Systems before, but its my first IBM. Also thanks for the links. I read them now.

the board may not need to be recapped. its just likely. The power supply is also likely going to be just fine.

Jackhead wrote on 2023-09-06, 17:58:

Many thanks guys! Sound like there is a lot of work to do. But also fun for me. My 55SX has a bad cmos battery. But it also in […]
Show full quote

Many thanks guys! Sound like there is a lot of work to do. But also fun for me.
My 55SX has a bad cmos battery. But it also include the Setup floppy. Still waiting to get the package.
Also good to know that i have to recap board and drive. I think than PSU also..
I did many retro Systems before, but its my first IBM. Also thanks for the links. I read them now.

As someone said, board recap isn’t most likely needed, but for floppy drives it is more than likely.

If that setup floppy doesn’t work, you can always download them from ardent tool and make the disk on some other computer.

Your first task is pretty much to check the operation of that floppy drive in any case. Everything else is pretty much useless if it isn’t functioning, because system is pretty much good as a large paper weight without a working floppy.

https://texelec.com/product/ibm-ps2-to-standa … floppy-adapter/

I bought 2.

he also has the sound card you are more than likely going to want. unless you have a passion for the pc speaker. Original cards are stupid expensive.

luckybob wrote on 2023-09-06, 18:23:

https://texelec.com/product/ibm-ps2-to-standa … floppy-adapter/

I bought 2.

he also has the sound card you are more than likely going to want. unless you have a passion for the pc speaker. Original cards are stupid expensive.

I think 55sx sx has the 34-pin drive, not an edge connector one so this adapter doesn’t work. Another crucial factor deciding a correct adapter is that if 55SX requires a media sensing drive or not. If so, it again needs a different adapter which became available just recently. Media sensing drive pinout and signals are completely different from standard drives and it needs some logic to work so the type of adapter you linked is not correct.

One fits all models type of adapter isn’t possible with these computers. You need to find out the specs of your system and then get the correct one.

Aren't these machines just glorious? Cant even use the same basic floppy disk between models.

luckybob wrote on 2023-09-06, 19:22:

Aren't these machines just glorious? Cant even use the same basic floppy disk between models.

They sure are 😅

In pictures i see my floppy has that 34pin ribbon cable attached. Ok so first focus on the floppy. Nice to see there new boards for it! (sound/ide)
Whats about graphic cards? Do i need one for early dos gaming ?

the onboard graphics are good enough for 95% of games. There are options out there, but anything beyond the IBM made cards is near unobtanium.

Jackhead wrote on 2023-09-06, 20:03:

In pictures i see my floppy has that 34pin ribbon cable attached. Ok so first focus on the floppy. Nice to see there new boards for it! (sound/ide)
Whats about graphic cards? Do i need one for early dos gaming ?

No, you don’t need graphichs card for it. It has plain VGA onboard graphics already. While it isn’t anything amazing, it still provides everything you need for a system like this. It’s not like you are going to play action titles that support SVGA resolutions with this system anyway.

Like previous poster said, there are IBM XGA graphics cards for MCA, which support higher resolutions. However, they like many other MCA cards, are rare and most likely pricey. You don’t get any benefits from it for gaming either so just stick with the onboard chip and enjoy.

At that age, IBM PS/2 are very expensive and one big minus, they are not ready to play with.

To do list:
Buy cards, parts, including battery, very specific memory module. Costly.
Rebuild floppy drive and replace grease that turned solid on the rails and screw drive motor. Very techanical and delicate job, you do not want to mis-align the heads.
Source the ADF files for the cards and create disks for setting up this.
Replace capacitors in the power supply and motherboard. Very skilled job and power supply are on endangered list, need to preserve them as long as they work.
Original, proprietary hard drives that works are now extinct. Really. Yes! Means you need to get new MCA IDE adapter. And solder together power harness, print a sled to power and hold the IDE hard drive or CF card.
SCSI is good way to go but again old hard drives are getting harder to find and increasingly expensive.

I know this. I had PS/2s and still have one model 70 that yet to be completed for several years now due to after-mentioned hard drive issue and lack of sound card, thanks to the new MCA IDE card, and new sound card I might get this one done.

Pentium-class clones using ATX motherboard form factor are cheaper to go this way and can be throttled down easily and still have ISA slots.

Cheers,

There are things in the pipeline to replace the special snowflake hard drives in these machines:

https://www.youtube.com/watch?v=u9cQ6WJdCyg

The big hangup is just the severe lack of demand.

Welcome to the wold of PS/2 from me as well.
For the memory, you will need parity modules with presence detect, where the PD bits can be easily changed using a soldering iron.
http://mcamafia.de/mcapage0/memorypd.htm
The IBM branded Future domain SCSI controller might be the best choice, if you want to go SCSI.
As allready mentioned, for an SD-card solution IDE ist the easier way to go.
For cpu upgrades snap on modules with 486slc exist. Upgrade to a 386DX will not work due to the 16 bit bus of the 386sx.
The Kingston 486 Turboboard is a 32 bit MCA board replacing the onboard CPU with the one on the card, but will not fit the 16 bit bus of the 55sx.
For anything sound related original boards are rare and costly, but meanwhile several newly designed boards are availiable.

Regarding the CPU upgrade: consider that (regular) 386 CPUs don't have a multiplier. So going from 16MHz to 33MHz doesn't just mean running the CPU twice as fast, but also running every single other component connected to it twice as fast. So you'd need to replace a lot more than just the CPU. That's what luckybob means with "not a snowballs chance in hell, unless you are already highly skilled in electronics" - and that's not even taking the 16b SX vs 32b DX stuff into account. Stick with the upgrade modules (if you are lucky and rich enough).

dionb wrote on 2023-09-08, 11:21:

Regarding the CPU upgrade: consider that (regular) 386 CPUs don't have a multiplier. So going from 16MHz to 33MHz doesn't just mean running the CPU twice as fast, but also running every single other component connected to it twice as fast. So you'd need to replace a lot more than just the CPU. That's what luckybob means with "not a snowballs chance in hell, unless you are already highly skilled in electronics" - and that's not even taking the 16b SX vs 32b DX stuff into account. Stick with the upgrade modules (if you are lucky and rich enough).

This. Although like ardent tool page of 55SX implies, using those processor upgrade cards in general with 55sx is not necessarily that straight forward in any case, even if you manage to get one. I'd just happily enjoy what 386sx offers. It is much easier (and cheaper) to build another faster DOS system for heavier tasks.

I can't help but chuckle when I keep reading about the issues, really weird solutions and in general the shenanigans IBM made with these systems. A good example about these stunning solutions is how to remove a password from locked 55sx, according to ardent tool system page:

To remove the password: […]
Show full quote

To remove the password:

• open the cover (hardest part of the operation...)

• locate the speaker cable from the front to the vertical bus riser card

• unplug the cable at the bus riser card

• turn it around by 180 degrees

• plug it back to the bus riser card

• close the cover.

Password is gone.

WTF!? Speaker cable? What kind of black magic is this!? Who came up with this!? 😁

Im a bit afraid after all that messages. I wonder if its more pain to setup as an Amiga or a PC-98 😀 . Anyway still looking forward to get my unit. At least the unit looks in really good shape, no rust or damage.
Here some pictures from the seller.