IBM PS/2 Model 50 (8550) September, 2018

PS/2 Model 50 - Part 2

After working on the PS/2 Model 50, I discovered that the hard drive was having issues. One thing I thought of was maybe the drive controller was the problem.

I grabbed one on eBay and noticed it looked a little different than mine, but it fit correctly and was recognized by the system.

Unfortunately, the controller wasn't the issue. With either of them, I got the same errors with the hard drive that I had.

I went back to eBay and looked for replacement hard drives. I was able to find some, but they all cost more than I paid for the entire system.

I decided to spend that money and grab the drive anyway. Turns out I bought a drive for a different PS/2 system, so I couldn't use it.

The seller let me return it and get my money back. I was then able to buy a drive that was actually compatible with this system.

I'll make this part short... every combination of drive/controller I used all gave me the same issue. I actually bought like 3 PS/2 hard drives, none worked.

I suppose you don't really need a hard drive to be able to use a computer. I have a working floppy drive, so I can just keep booting MS-DOS (or even IBM PC-DOS) from disks.

I don't want to give up on this system, but it was making me very frustrated. In order to take my mind off of the hard drive situation, I decided to do another upgrade.

I grabbed an Intel 80287 off eBay and instaled that into the slot on the motherboard. I don't know what software really uses this, but I thought it would be cool to add one.

After installing the Mountain card and its ADF file, I thought that would be all I'd need to get a hard drive working. Figured I could just connect the drive and boot up the system.

With the drive connected... nothing happened. Booting to DOS (from a floppy), there is no C: drive, and fdisk cannot see anything. Why is this happening? I'm pretty sure I connected everything right and I don't think I need a terminator or anything.

Searching around, I figured out what was wrong. It looks like this SCSI card is only for tape drives. The issue is that this card does not have a BIOS option ROM. That's what I need to be able to boot from a SCSI drive.

I wasn't sure if I could continue with the system. I could continue to just boot from a floppy disk, but I really wanted a hard drive. I was getting frustrated with all the hard drive solutions I've tried not working. I decided to make an eBay saved search for "MCA SCSI" and just left it alone.

I forget how long it took, but one day I got an email from eBay that my saved search had a match! I wasn't sure I really wanted to spend more money or time on this system, but I also just wanted to get it working. I tried my best to verify that this card had a BIOS Option ROM and would actually work here. It seemed like it did, so I bought this card, hoping it would finally solve my issues.

When the card arrived in the mail, there was a floppy disk included with the ADF file to enable the card in the system's BIOS. I installed the card, used the reference disk to load the ADF file and powered the machine back off to connect the hard drive to test.

For now, I am using a SCSI drive that seems to be from a Mac of some sort and an external molex supply. I'll figure out a power solution once I can confirm the card/drive works.

After connecting the drive and powering on the system, to my surprise a "Future Domain" screen appeared! That is the BIOS Option ROM running and detecting my hard drive!

Booting off of a floppy disk, and I was correctly able to run fdisk/format on the drive! Success! I finally had a drive controller that could read and boot off of drives!

Now it's time to somehow mount the hard drive in the system and get power to it without an external molex PSU.

For those curious, the card is a Future Domain MCS-600.

I screwed the drive onto the original drive sled, so I could mount it in the case. The screws didn't line up... well one did. One screw ought to be enough.

Now I need to get some power to the drive. I was using an external molex power supply, and now I need an internal source of power. There is a molex connector on the SCSI card, but I don't have the correct cable for that.

My solution was to solder a molex cable into the system itself. You can solder wires to the back of the floppy connector board. It's actually pretty simple, following the instructions found here.

I suppose I could've soldered together a molex-to-molex cable to use the card's power socket, but I liked the idea of the system itself providing the power, in case I ever want to swap out the SCSI card (even though I don't see why I'd ever do that).

For now, I am calling this a success! Now I can install MS-DOS (or maybe even IBM's PC DOS) on it and start using it.