Fixing Up an IBM Model M2 Keyboard

A few weeks ago I picked up a Model M2 keyboard from eBay. I'm not a raving fan of mechanical keyboards but I definitely agree that they are quite nice to type on. I actually got a Das Keyboard Model S Pro years ago but haven't used it recently since it's a Windows keyboard layout and my modern computer is a Mac and I've just grown to hate using Windows keyboard layouts on Mac. But otherwise, it's quite nice and I wouldn't hesitate to recommend a Das Keyboard to anyone. Unicomp also makes apparently very nice mechanical keyboards along the style of the original IBM keyboards but I've not tried these personally.

At any rate, I picked up this Model M2 to use with my "retro" computers. Not really for any particular reason other then it feels era-appropriate and is a nice relatively compact buckling spring keyboard. Many more people would prefer the original Model M over this, but I've always been put off on getting one of those due to the bulky size.

The Model M2 is infamous for having bad capacitors. The two capacitors on the controller inside will apparently go bad (dry out) quicker if unused for long periods of time, so even a brand-new-in-box M2 keyboard isn't guaranteed to work.

And as if bad capacitors weren't bad enough, the M2 is also infamous for being difficult to take apart and to reassemble (probably harder to reassemble then to disassemble I think). Apart from two screws on the bottom, the majority of the keyboard is held together by somewhat easy-to-break plastic clips internally that need to be very carefully opened. Oh boy.

It should be noted that not all Model M2 keyboards are mechanical. Certain ones made by Lexmark with a model number beginning with '7' are rubber dome. But otherwise from the outside they look identical.

This one I got arrived and initially didn't work when I plugged it in to give it a try it. It gave the tell-tale sign of bad capacitors where only two LED lights flashed on and stayed on and no key-presses were ever registered. However I noticed that by unplugging it and replugging it in that it worked perfectly. I continued using it for a couple weeks like this and all was good, but I knew that this wasn't a long-term solution and that I really did need to go and replace the capacitors.

Onwards to disassembling!

First thing is first. Take a picture of the keyboard before you take anything apart. This is so you can use it as a reference for where the keys all go when you're putting it back together.

To begin, the keycaps all need to be removed. This is because the aforementioned plastic clips that hold the keyboard together are underneath the keycaps. And you'll probably want to clean the keycaps anyway. Mine actually weren't that dirty as you can see from the above photo, but I still cleaned them anyway.

Removing the keycaps is really simple. You can use any thin flat tool to pop them off. I began by popping off all of the square keys. A number of the longer keys such as Backspace, Enter and the space bar have additional little brackets that attach to the bottom that need some extra care, so it's best to save these for last.

With keys like Enter shown above, I found it easiest to pop up the keycap first in the same exact way as I'd done for every other square key, but before trying to lift it off completely, you take a some dull flat/thin tool and press down the bar so you can easily slide it out. It's very easy, but you do need to be careful as the plastic that holds the whole bracket to the keycap is very thin and easy to break!

The space bar is a little bit different then all the other keys. Again, I started by popping it up in the same way as the other keys, but again, before trying to lift it off, you need to release the bracket. This one is different then the other brackets and is held down by two little bars that need to be pushed out. You push the left one out to the left and the right one gets pushed out to the right. Use a dull, flat, thin tool again to push them out. They are a little tough to push out, but once you get the first one the second one is easy. Again, be very careful as the plastic is thin and easy to break!

Now the keycaps are all removed.

At this point, you'll want to take another picture. This is important because as you can see, not all of the holes have springs in them! All of the missing springs are the extra holes that are covered by the longer keys which all only need one spring each just like the smaller square keys.

If you're cleaning the keycaps, get some soapy water ready and let them soak for a good hour before doing any scrubbing. That'll give you plenty of time to do the rest of the disassembly and maybe even get the capacitors replaced too depending on how things go.

As you'll be able to see in the above picture of the keyboard without the keycaps on, there are 13 small plastic clips that need to be separated to remove the top plastic half of the keyboard. You again use your dull, flat and thin tool to separate the two plastic parts of the clip, but I found that they would not stay separated and trying to push down to move the other half of the clip lower so it would not reattach was tricky and not guaranteed. The whole plastic of the keyboard is somewhat flexible so if I got one clip to stay separated, once I picked up the keyboard there was a very good chance the whole thing would flex a tiny bit and the clip would somehow find its way back and snap together again. Super frustrating!

So, I figured I needed something to wedge many of the clips apart while I pried off the top plastic cover on the keyboard. Not having much in my apartment to use for wedging, I turned to my little stack of spare computer expansion slot/bay covers. This actually worked much better than expected and I was able to turn the keyboard on it's side to begin prying it apart with the confidence that the clips would stay apart.

If you decide to go this route, whatever you use as a wedge should really be thin and hard (so as not to bend/flex while wedged in the clip). A very common complaint about these keyboards is the ease with which these plastic clips break, so you really don't want to flex them more then you have to!

As you can see in the photo on the right, you need to pry apart the top and bottom halves of the keyboard from the side. I started from the bottom and once I got it apart enough, used my finger nails to keep it apart while I worked on the top half. Eventually got it open enough to fit the tool I was using in. By this point, the expansion slot cover wedges that were closest to where I was opening the keyboard from were falling out, as expected, since there was nothing to hold them there once I started opening it.

I only had enough wedges for half the keyboard, so once I had it open enough so that the first 5 of the wedges had fallen out, I used my tool as a bigger wedge and left it placed between the two halves of the keyboard, set the whole keyboard back down and re-used those expansion slot cover as wedges, placing them into the remaining plastic clips on the opposite side of the keyboard. At this point, all of the plastic clips were either already apart or had a wedge in them and I was simply able to somewhat gently but firmly pull apart the top and bottom plastic halves of the keyboard as if I was slowly and carefully opening a book.

Luckily for me, I did not end up breaking a single plastic clip in the process! Hooray! Even if you broke a couple clips, it's not the end of the world. Hopefully though you don't break too many. If that does happen I imagine you could probably use a bit of hot glue to put them back in place.

I should point out that all the while you will probably notice and hear/see the buckling springs inside falling out of their place. Don't worry about this, but definitely do not try to close the keyboard again at this point else you'll probably squish and ruin some of these springs after they've been freely moving about inside. Just keep going with opening the keyboard and it'll all be fine.

Take all of the springs and carefully place them someplace safe for now, out of the way. We won't need them until we begin reassembly. You should also carefully peel up the thin black sheet/mat that the springs were sitting on. You can clean this if you like. I just brushed it off lightly with a dry cloth and then set it aside.

Some people report finding that the traces on the membranes corrode and go black or dark brown or whatever. As you can see, I didn't have that problem. Not sure what people do to fix that problem so unfortunately I cannot advise there. I would not recommend removing any of these membranes if you don't see any problems on any of the traces. It looks like it would be tricky to get them all back perfectly aligned and I've read comments from people saying as much. Just leave them as they are if you can.

And now the problem capacitors. You can kind of see in this photo that some of the contact pads underneath the capacitor has gone all dark brown, due to the capacitors starting to leak out. After seeing this, I was kind of surprised that the keyboard had worked for the couple weeks I'd been using it so far. I scraped off as much of the dark brown gunk from the solder as I could using my pocket knife, being very, very careful to not scrape any of the surface of the PCB surrounding it. Once I'd got enough of it off that I could see mostly solder, I got out my soldering iron.

You could of course try removing the controller PCB from it's position in the keyboard. As you can see there are several plastic clips holding it in place. It seemed that it would be quite tricky to remove to me, so I decided that I didn't want to risk breaking these clips. These capacitors are surface-mount, not through-hole, so technically there is no actual need to remove the PCB anyway in order to remove them. Plus it's only two capacitors and there is enough of the contact pads visible on each of them that I figured I wouldn't need to apply much heat anyway so there wasn't likely to be any harm caused by doing the whole re-capping with the controller left where it was.

Post-removal, I was left with more of a mess to clean up from all the leaking that had gone on over the years. Unfortunately I also pulled up a bit of the bottom contact pad while removing the smaller capacitor on the left. Whoops. With that in mind, I'm not sure I'm the best person to explain the process of using your soldering iron to remove these capacitors. But if you do still want to know what I did, basically, I just heated up the exposed area of one of the contact pads and gripped the capacitor with a pair of pliers and twisted the side being heated up away after I could see the solder had melted. Then repeated the same process for the other side. I think my problem was that I tried twisting the capacitor too soon when the solder wasn't melted yet, so twisting the capacitor away just ended up ripping up the contact pad in the process.

I used 99% alcohol and Q-tips to clean up the remaining gunk from the leaking old capacitors. I initially used my pocket knife to scrape up some hard bits without really thinking about it and ended up scratching a bit of the PCB. Dumb, dumb, dumb! Thankfully I didn't end up cutting a trace or anything. After this close-call I decided to just use my fingernail to scrape off the remaining bits of hardened gunk.

The replacement capacitors needed are a 2.2µF 50V and a 47µF 16V. You can of course go higher with the voltage, but should definitely keep the capacitance the same in any replacements you decide to use. Specifically, I used these two capacitors that I got from DigiKey.

I placed little squares of electrical tape down as a precaution. I wasn't sure if the capacitors would get pushed down and by how much (potentially putting the side of them in contact with the PCB) once the top of the keyboard was placed back on. Maybe it wasn't needed. Also, certainly anyone could do a better job of soldering then I did here, heh.

Before reassembling, it's important to test this out and see if the new capacitors are doing the trick. I took the keyboard over to my computer, plugged it in and powered it on and voila, no more stuck LEDs after a cold boot (without my previous unplugging and replugging it in trick)!

You can simply tap your finger on the membrane to test keys. I tested a bunch this way to make sure that everything was working fine.

At this point, it had been over an hour because I am kind of slow with these things. So it was about time to clean up all the keycaps and the top plastic cover of the keyboard. Once this is done, I set them all out, face up, on a towel and let them dry for a few hours. I actually used my DataVac Electric Blower Duster to dry off the top cover quicker as I wanted to get on with the reassembly sooner. But I did leave the keycaps to dry on their own for a few hours in the meantime.

To replace the buckling springs, you need to take the top plastic half of the keyboard and set it upside down, but with something to mount it up a bit higher. This is because when the springs are placed inside, the top of the spring will dangle slightly past the top of the plastic cover. So if you had it just resting flat on some surface you would not be able to correctly and fully insert each spring into it's little bracket. As you can see here, I'm using two hard disks on either side (because they were the only really suitable thing within reach as I sat down to do this, heh) to mount it a bit higher.

Then, using your previously taken picture of the top of the keyboard before you took it all apart, re-insert each spring into it's bracket, leaving the correct few spaces empty. It is absolutely important that each spring fits snugly into it's bracket on the keyboard cover. However, there's nothing to hold them in place other than gravity, so just be careful. When you're done this process do a quick once-over to ensure that they are all snugly in place. Trust me on this!

Now take the thin black sheet/mat that we removed and set aside before. Place it over top of the springs. Each of the holes in the sheet should line up with the various holes for the clips and two screws on the plastic cover. Unfortunately there is nothing to hold this in place.

And now is probably the worst part. We need to take the bottom half of the keyboard (that has the membranes and controller PCB in it) and place it on top of the top half of the keyboard with the springs in it. AND we need to do it while it's mounted slightly off the ground as we have had it thus far. This is incredibly important as otherwise the springs will pop out of place. In my case, holding the bottom half of the keyboard upside down did not result in the membranes falling out, but I would guess if that happens to you that you could use some small bits of tape to hold it in place. In my case, the black sheet would not stay in the bottom half of the keyboard while held upside-down so pre-placing it on the top half as shown in the above picture worked best for me.

Carefully hold the bottom half of the keyboard over top of the top half, lining it up while being careful not to accidentally shift the top half off of it's two supporting mounts and then set it down, pushing it together. DO NOT pick up the whole thing to attach the two plastic halves together You definitely want to leave the top half with the springs in it resting on your two mounts throughout the entire process. Go around all the edges and use your hands to squeeze all the edges together and you should hear all the plastic clips clip into place. If you pick it up (even slightly) to do this, you risk the springs falling out of place!

Apparently this exact problem happened to me with exactly one spring. Once I had reattached all the keycaps I was testing all the keys and noticed that the 'W' key didn't work unless pressed "just so." Taking off the keycaps again, I took a flashlight and looked down at the feet of the buckling springs.

It's maybe a bit hard to see in this picture, but the black feet of the spring for the 'W' key is very slightly crooked. The foot on the left side had somehow shifted out of place during reassembly and was outside of the plastic bracket that it should be sitting in. This was resulting in the key not pressing correctly (even though the sound of it pressing was just the same as every other key that worked fine). The fix for this was to take it all apart again and reassemble it. Not fun. So, be very, very careful when reattaching the bottom half of the keyboard to the top half with the springs in it! Take your time with it.

Once you've got that done, reattaching the keycaps is easy. Start with the spacebar and then do all the longer keys. Leave the simple square keys to the end as they are the most straightforward.

With every keycap, the goal is to have the top of the spring resting in the middle of the underside of the keycap. As you can see in the photo on the left, there is a small round slightly raised piece of plastic inside the bottom of the grove in the middle of the keycap. The top of the spring when inserted correctly will rest perfectly around that small round piece of plastic.

What is somewhat likely to happen when you're replacing the keycaps is that the spring gets caught on the open flat area at the top of the grove, or it ends up resting somewhere on the little plastic ramp thingy on the other side. If this happens you need to pop off the keycap and try it again. You'll know when you got it correct when you're able to press the key down and it makes the very same clicky sound as it did before you took it off in the first place. It it feels too mushy and, most importantly, does not make that clicky sound then the spring is not in the correct position. If you're not sure if it's making the correct clicky sound, assume that it's not correct and try again. If you're still not sure, try replacing a few other keycaps and compare the sounds.

Most of the longer keys have more than one grove. The grove that the spring goes in is always the one that has the top/bottom of the plastic cut away, as you can see in the photo on the right. I had a lot of trouble getting the number pad '+' and Enter keys on correctly. The springs just kept not sitting right when I popped the keycap back on. What ended up working for me was to tip the keyboard up, so it was resting on the top edge (IBM logo down), forcing the spring to be naturally a little lower (due to gravity) as I was inserting the keycap.

As you're replacing the longer keys with the bar/bracket thingy, use a tool to push the bar down slightly (and very carefully, you don't want to push it too much and break it!) so it fits under the clamps.

Finally, remember to replace the two screws on the bottom.

Heh, you probably can't even tell at a casual glance that that is a different photo then the first one I posted because the keyboard was relatively clean to begin with. This photo is definitely post-cleaning-and-fixing!

And that's pretty much it! I hope this helps someone out there. There are a number of guides to repairing and disassembling/reassembling the Model M2 keyboard that other people have written over the years but I always felt like there was some details missing, particularly with regard to disassembling. I wrote this post thinking about what details I would have loved to have going into this. It ended up being quite wordy, but well, sometimes (often) more details are better!

My Custom 486 DX2 Build

Since it's basically complete now, I figured I'd post something detailing it. Actually, it's been mostly complete for a while now, but the last couple small touches came together this week.

Despite the fact that I got a perfectly capable mini 486 PC earlier this year, I still decided I wanted to build my own similar system in a baby AT form-factor case. This way I could customize it more to my liking. I also really wanted to use a specific style baby AT case that matched the old 386 PC my family used to have. It's nothing special at all, but it's kind of stuck in my head over the years and become synonymous to me with "old DOS PC", so I pretty much was unwilling to let this "requirement" of mine go.

I began picking up parts during the summer and piece by piece I've finally got everything assembled. Strangely enough, getting the particular AT case I wanted was hardest, even though from what I gather it was actually a very common style case back then. Maybe just a coincidence that I had a hard time finding one.

Actually this ended up being the second case of this style that I received. The first one was shipped and arrived broken (the plastic front was cracked and broken in multiple places). Got pretty lucky that I was able to get a second one now that I think of it.

So, what's inside? Let's take a look:

  • CPU: Intel 80486 DX2 SX911 66Mhz
  • Motherboard: FIC 486-PVT, 256KB L2 Cache
  • RAM: 16MB
  • I/O Controller: Promise Technology 560C PDC20630, VLB
  • Graphics: S3 Trio32 2MB, VLB
  • Network: 3Com 3C509B-TPC
  • Sound: Sound Blaster Pro 2.0 CT2600 and Gravis Ultrasound Classic 3.74 1MB
  • Hard Disk: Quantum Maverick ProDrive 540MB 3600RPM MV54A011
  • Floppy Drive: 3.5" 1.44MB Sony MPF920-E and 5.25" 1.2MB Teac FD-55GFR
  • CD-ROM: Torisan 6x CDR-S16
  • Power: Athena Power AP-AT30 300W

Since I ended up getting basically every piece separately, it almost certainly ended up costing a bunch more then it would have if I had bought some pre-assembled PC from eBay or some other place (which people do sell, tested and working, even today). However, given all the trouble I had to go through to get this working, it really feels a lot more satisfying having gone this route.

As one may expect given the era, contrary to building a PC today, a lot of things did not "just work" together out of the box with this PC. This is especially the case when talking about VESA local bus (VLB) hardware where stability was a common problem. Having to adjust jumpers on the motherboard and the different ISA cards to get the settings just right is quite a different problem from today's PC hardware. This can be even more difficult a task today because for some motherboards the documentation is sparse or even outright missing, leaving you to either have to figure it out by trial and error, or hope the (often limited) labels printed on the motherboard or ISA cards themselves are complete enough and self-explanatory.

Luckily for me, with this particular motherboard I was able to find PDF scans of the original manual. The other card that you'll usually want a manual for due to all the jumpers on it is the I/O controller. In my case, I was unable to find a manual, but the labels printed on the card itself were sufficient enough to get it working properly.

Well, actually, I'm not sure on that last bit to be honest! It did seem to be working perfectly fine up until a week or so ago where I started having problems with the BIOS detecting the hard disk. I thought at first that it might have been an indication that the hard disk I was using was dieing or dead, but after swapping it out for another, using a totally different I/O controller card and also trying different IDE cables, I was unable to eliminate the issue. And to make matters worse the issue only manifested itself sometimes. The only thing I've found so far that solved this problem was to connect all of the IDE devices to the IDE channel that runs on the ISA bus instead of VLB. This isn't too big a deal, as I believe that since I'm running DOS 6.22 primarily that I don't see any benefit whatsoever to having the hard disk running over VLB.

It is worrisome though that the problem only started to occur just recently and seemingly not a result of any other hardware changes (since it had been a while prior that I had made any). Either some other component in this build is starting to become a little flakey, or this is just the fabled VLB stability problems I've heard about rearing it's ugly head. At any rate, something I need to keep an eye on.

Two sound cards probably seems strange at first but there is a reason for both. Sound Blaster is a pretty typical card for the era. The Yamaha OPL chip on this one (and many other Sound Blaster cards) has a pretty recognizable sound that I quite like. And it's compatible with a great many DOS games, so it was an obvious choice.

The Gravis Ultrasound however is something I had never seen before, only heard of, and certainly was not nearly as common a choice at the time. It's an interesting card however, as it was one of the first (if not the first?) sound cards to support hardware mixing of multiple sound sources. Sound Blaster cards couldn't do this, requiring programs to implement their own software mixer which took up valuable CPU resources. In practice, this ended up not really helping many games that supported the Gravis Ultrasound though as almost all of these games supported Sound Blaster too and in an effort to keep the code simpler, would implement their sound engine to the lowest common denominator. This meant not utilizing the Gravis Ultrasounds hardware mixing support since no other card had it.

However, what I really wanted a Gravis Ultrasound for was for it's subjectively better sounding FM synthesis / MIDI playback. So far every game I've compared that supports both Sound Blaster and Gravis Ultrasound sounds better (to me) when configured to use the latter. In some cases, such as with One Must Fall 2097, the difference is objectively better.

For a 486 computer, VESA local bus graphics are pretty unique, and until PCI came around (which was quite soon after VLB was introduced), it provided the fastest graphics you could get. To me, it feels almost necessary to use VLB with a 486 machine since you cannot use VLB with anything else. Everything beyond this hardware level would be PCI and eventually AGP. Everything before, ISA. Using an S3 card is a pretty solid choice. All benchmarks I've seen and done personally have them as top-tier cards of the era. Compatibility is also excellent. Probably a more common choice would've been a Cirrus Logic card though.

Nothing much else to say really. A 6x CD-ROM feels mostly right, maybe a little bit fast for the era? I remember we had a double-speed CD-ROM in my family's 386. A 500MB hard disk is also quite large for a DOS PC really. It's funny to think of that, but then again, I remember my family's 386 had a 20MB hard disk and at the time I thought that was large! 16MB of RAM is plenty for a 486. Most DOS games would need less then 8MB of RAM, so 16MB is nice to have the option for running SMARTDRV, or using a RAM drive, etc. My DJGPP boot configuration sets up both and it makes a significant difference with compile times, still leaving 8MB of RAM free for everything else.

Follow-up: Unisys CWD 4001

I figured that I would post a follow-up regarding the Unisys CWD 4001 mini 486 PC I picked up earlier this year. I've had a few people now ask me various questions about it. It is certainly an interesting PC, especially for those looking for a nice compact retro PC to play around with so I certainly don't mind posting some more information about it to help out anyone else with questions regarding it.

Almost six months later and I'm actually not using mine that much, as I ended up building another 486 PC in a baby AT case. This was mainly because I wanted to be able to toy around with different hardware customizations, have more options for sound cards and have internal CD-ROM and 5.25" floppy drives. Otherwise my CWD 4001 is still working perfectly fine.

Hard Disk

As mentioned in my previous post earlier this year, the hard drive it originally came with died so I replaced it with a CF-to-IDE adapter. I got a StarTech IDE2CF and a Transcend CF200I 512 MB Compact Flash card. I had to cover the bottom of the adapter with electrical tape as otherwise some of the pins on the bottom would short against the metal part of the case it is resting on (and I could not find any kind of mounting bracket to fit in there instead).

The jumpers I have configured on the CF to IDE adapter set it for 3.3V power and master mode, drawing external power from the adapter you can see plugged in in the photo.

The BIOS configuration that I use for this is 987 cylinders, 16 heads, 63 sectors. If you end up using a CF card to replace a hard disk, make sure you do a FDISK /MBR or you may end up puzzled for a while like I was as to why you are mysteriously unable to boot from it!

You should be able to use a larger CF card if that's all you have (for a short while I was using an 8.4GB IDE hard disk without issue). Though with MS-DOS 6.22 you will only be able to use partitions with a max size of ~500MB.


Mine came with an AMD 486 DX2-66 already and that's what is still installed as I write this. However, these should work fine with up to a DX4 (some even had a DX4 pre-installed). On my CWD-4001 there is a voltage regulator on the motherboard so this should support 5V and 3.3V CPUs just fine, but I've not actually tried this. Do your own research first before trying!

On the underside of the motherboard on my CWD 4001 there is a motherboard diagram showing jumper settings. I've heard some people didn't have this, so I'll share what mine looks like:

The CWD 4001 doesn't include any L2 cache but since these are 486 machines, I believe all CPUs that these would ever have shipped with had 8KB L1 cache. The BIOS has an option to enable CPU write-back cache so if you have, for example, an Intel 80486 SX955 (P24D) then you can make full use of it. Though you will also have to configure the jumpers as shown in the diagram above. However, probably most people won't have a CPU with write-back cache support. Not to worry if you don't, it doesn't make a massive (real world) performance difference anyway.


For MS-DOS, you'll want the NE2000 packet driver. Then you'll want to add this to your AUTOEXEC.BAT with something like the following:

C:\NET\NE2000.COM 0x60 10  

Where the 10 is the IRQ for the network adapter. Mine was set to 10, yours might not be (IRQ 10 or 11 were very commonly used for network adapters). I didn't have to tinker with any BIOS settings to make this work (not that there really is much of anything that you could change that would affect this to be honest).


As mentioned in my previous post, I'm using a Creative Sound Blaster CT4170 (Vibra 16XV). Your options for sound cards are quite limited with a CWD 4001 due to the compact size of the case. As far as Creative cards go, you'll probably be stuck to only a few of the later models that were more compact. Probably the best choice is one of the AWE64 value cards that is more compact but I don't own this card personally. I'm unfamiliar with what other Sound Blaster clone cards may fit.

For me, using IRQ 5 and 7 both worked. Remember that IRQ 7 is also used for the parallel port (LPT1), so if you're using any parallel port device you may want to configure your sound card to use IRQ 5 instead.

I have the following in my AUTOEXEC.BAT for my CT4170:

SET BLASTER=A220 I5 D1 H1 P330 T6  


The CWD 4001 I would say is pretty average for a 486 DX2-66 system. It does not have VLB graphics, but the Cirrus Logic GD5424 isn't too bad really. The lack of L2 cache is also unfortunate, but the RAM speed seems a bit faster than other 486 systems I've tried... maybe something specific to the chipset/motherboard? Not sure really. The two RAM sticks installed in my CWD 4001 are nothing special, two HYM532220W-70 (72-pin 8MB 70ns) sticks.

Versus the other 486 system I built (Intel 80486 SX911 CPU, FIC 486-PVT motherboard, S3 Trio32 VLB, 16MB RAM) just for a slightly apples-to-oranges comparison:

How does this translate to "real world" performance? Well, I can share with you the results from running Phil's DOS Benchmark Pack on both of these systems:

CWD 4001 FIC 486-PVT, SX911, S3 Trio32 VLB
3DBench 1.0 41.6 fps 50.0 fps
3DBench 1.0c 40.4 fps 48.2 fps
Chris's 3D Benchmark 26.9 fps 31.4 fps
Chris's 3D SVGA Benchmark 9.1 fps
PC Player Benchmark 10.1 fps 9.6 fps
PC Player Benchmark (640x480) 4.0 fps 3.8 fps
Doom (min. details) 71.4 fps 70.0 fps
Doom (max. details) 24.3 fps 26.1 fps

Not really too surprising here when comparing ISA graphics to VLB graphics (in particular the S3 VLB graphics cards tended to be top-tier, performance wise).


A few people have asked questions after obtaining their own CWD 4001 (or 4002) after seeing that they were missing some internal components. In particular I've seen some people missing the ISA riser card and/or the bracket that fits onto the inside back of the case which the back plate of an ISA card would slide into when installing one. I'm unsure what people are doing for replacements for these and even if they are easy to come by, but for people's reference I've taken a bunch of photos of the ISA riser card and the ISA back plate bracket thingy.

Anyway, I hope the above helps anyone else looking for information about these Unisys CWD mini 486 computers. Feel free to email me though if you have any additional questions of course (my email address is on the "About" page linked on the left).

Mini 486 PC: Unisys CWD 4001

UPDATE: I posted a follow-up here where I go into to more details about this PC which may be of some interest to you.

A couple weeks ago or so, I came across a forum post with someone showing off a mini 486 PC by Unisys. After a bit of searching, I discovered that there was a seller on eBay who had a bunch of these for sale so I would easily be able to get one. When I saw this, I instantly thought to myself "I must get one of those!"
EDIT: It seems a video someone posted about these got a bunch of people buying them from this eBay auction which in turn caused the seller to bump up the price considerably. I only paid $97 CAN for mine!

However, I decided to sleep on it and wait a few days first and see if afterwards I still wanted it. I had originally decided that I did probably want to either buy or build a 486 PC at some point -- actually scratch that. While I had initially thought it would be cool to go as far back as a 486, when I thought about it some more I realized that getting at least a Pentium would probably make more sense. This was because in addition to wanting to use it for some "old school" development purposes, I'd also definitely want to use it to play games. And a 486 wouldn't cut it for that use for me personally. And with this thought in my mind, the question of what exact hardware specs I should go for was left unanswered and I realized that I had to do more thinking on it all. And regardless, I wasn't in any rush as I was still having fun fiddling with Amiga-related things.

Well, after a couple days passed by I still found myself thinking about it quite a lot. Space is at a bit of a premium for me as lately I keep buying random electronics toys that I don't really need. But what other small 486 PCs am I likely to find or be able to build myself anyway? Plus it wasn't that expensive (well, shipping to Toronto cost more than the PC itself, but even so, I can afford it ... meh). So I bought one!

It arrived pretty quick (4 days). And my god, it is small!

There's little information out there about these that I was able to find, just a few web pages with spec lists and some French videos on Youtube from some guy doing both an overview and a tear-down. Evidently, the exact hardware that these come with can vary a bit, but mine was:

  • Model: Unisys CWD 4001-ZE, Manufacture date: Sept 10, 1995.
  • CPU: Am486DX2-S 66MHz, socket 1 LIF PGA 169-pin with star-shaped heatsink.
  • RAM: 16MB. 2x HYM532220W-70 (72-pin 8MB 70ns DRAM).
  • Graphics: Cirrus Logic CL-GD5424, 1MB VRAM
  • Network: Accton/Unisys UK0022 (based on Novell NE2000)
  • Sound: PC speaker
  • Hard Disk: Fujitsu M1612TAU (545MB) IDE
  • Floppy Disk: Teac FD-05HG-4684-U (Slim)
  • Expansion: One unused ISA slot
  • Ports: 15-pin VGA, DB25 parallel port, 2x DB9 serial port, 2x PS/2 port (keyboard/mouse), RJ45 network port
  • PSU: Built in (proprietary).

Total dimensions: 29cm x 22cm x 6cm (width/depth/height).

Here's what the motherboard looks like for those curious (click for full picture):

In the above picture, the floppy drive, hard disk, and ISA riser have all been removed of course. But with them all in there it's packed in pretty tight! I was a little bit concerned about what the temperature might be like when it's been running for a while, especially since the only fan in the whole computer is a small one for the PSU only.

Honestly, I'm quite happy with these specs! I knew it was possible that these could come with anything from a 486DX2 33MHz to a 486DX4 100MHz, and I was hoping for at least a DX2 66MHz since it's what's largely regarded as a minimum spec necessary for playing games like Doom at a decent speed (you can do it with less of course, but then it all depends on your tolerance for lower framerates). 16MB of RAM is plenty and for a 486, you won't need any more at all. I was a little bit unfamiliar with the graphics cards of this era since I was younger at the time and had no money anyway, so I just used whatever was available to me (heh), but a GD5424 with 1MB VRAM is not too shabby either. Not amazing, just average really. Onboard LAN is quite nice, means I don't have to use floppy disks to transfer stuff to it since it's obviously lacking a CD-ROM drive.

Aside from the lack of a CD-ROM drive, the other big thing that is missing is sound. With no onboard sound capabilities aside from the lovely PC speaker and with a single ISA port available, getting a Sound Blaster card seemed like the obvious next step.

Of course, since this is such a small computer, one needs to take into account whether any given expansion card will actually fit into the case. Most of the better Sound Blaster card options are unfortunately too long.

I eventually settled on two possible options: a Sound Blaster AWE64 or a Sound Blaster Vibra 16XV. The few people I could find that had these computers all seemed to go with the AWE64 (something like a CT4520 is small enough to fit). I ended up going with a Vibra 16XV CT4170 mainly because I found one locally for cheaper, but would've gone for an AWE64 otherwise myself.

The only other thing of note was that within a few days of having this computer, the Fujitsu hard disk it came with died. I didn't intend to use that disk over the long term and had already ordered a CF-to-IDE adapter to replace it with. However, since the adapter hasn't arrived yet, I ended up replacing the drive temporarily with an 8.4GB Maxtor drive I still had sitting around. The BIOS only recognizes 2GB and is only able to boot from a partition that is 504MB (max) however.

For the first several days I was using an old SyncMaster 943N 19" 4:3 LCD monitor but grew tired of the poor upscaling of low MS-DOS resolutions. Picked up a cheap CRT monitor (a 15" Sony Trinitron CPD-100SX) from someone on Kijiji and now I really feel like it's all come together as a real old-school DOS PC!

In the above picture, the text editor on-screen is RHIDE for use with DJGPP. I was fiddling with some VGA Mode 13h C code... a nice trip down memory lane.

Overall, I'm glad I got it. It runs great, it's quiet, for a 486 it's decently specced and runs pretty much any games I throw at it from up until about 1996 or so (then you start getting into games really intended for Pentiums). Even Duke Nukem 3D is playable at 320x200, though barely. I actually think that the CF-to-IDE hard disk would help here as I do notice the game does load stuff from disk during game play here and there, and it seems like those disk accesses usually correspond with a slow down.

After the computer has been running for a while, the PSU does heat up quite a bit and the case does get warm to touch on that side. It still does concern me a little and I might investigate to see if I can get a better fan. Also, I would hope that once I remove the "big" hard disk and replace it with a much smaller CF card that it might help improve airflow inside the case and possibly reduce the internal temperature a little bit. However, from what I can tell from the few other forum posts that I've found from others who own this computer, heat doesn't seem to be a problem. So, fingers crossed that it remains that way as I'm not sure what else I could do (nowhere inside the case that I could install an additional fan or anything like that).

Some Upgrades

A number of nice upgrades arrived over the past week or so.

The most significant honestly is the Amiga RGB cable. I'm no stranger to using RGB video for game consoles, but having been stuck with only Composite video on my Amiga 500 for the first two weeks that I had it, and then suddenly switching to RGB reminded me of what a huge difference in quality that switch is. Awesome.

Next up is an accelerator I bought, the ACA500plus:

This is honestly quite overkill for what I really want out of it, but it's probably nice to have all of it's features available anyway.

I primarily wanted a hard disk or some other non-floppy disk storage medium available. This is really just because we all know that floppy disks aren't super reliable over the long term. I've bought a few boxes of sealed double density 880K (1MB raw) floppy disks as well, but it is nice to have some more reliable storage medium available.

Getting something like an A590 would probably cost at least as much as the ACA500plus, and wouldn't offer any of it's other features. The Amiga 500 doesn't really have any other hardware options for adding hard disk-like storage (as it doesn't have any kind of IDE controller built in).

The ability to have a full 8MB of RAM is also nice as an option, especially so once I get into using C compilers. And the CPU overclocking ability (14MHz guaranteed stable, higher without the guarantees) is nice too, though I will probably keep at it the base 7MHz, as my goal has always been to work on projects that are targeted for the Amiga 500 specifically.

I have mixed feelings about the extra RAM being enabled or not. One thing I hadn't realized about Amigas (at least in Workbench 1.3, not sure if this changed with newer versions) is that when you have large partitions mounted, the system ends up using larger amounts of RAM (probably for some caching purposes? not sure exactly). So if I'm using the hard disk ability of the ACA500plus, leaving the extra RAM also enabled is a very good idea else the base 1MB (with 512KB trapdoor expansion) gets used up super fast. However, I need to make sure I don't get lazy with memory usage in my projects and make them incompatible with the baseline spec.

Final upgrade that was a nice change was a new power supply for both an Amiga 500 and Commodore 64, custom made by Ray Carlsen:

Since the Amiga 500 I got is from the UK, it came with a European power supply which of course is 220V which means I was forced to use a step up voltage transformer in conjunction with it. This was kind of annoying, and both the original Amiga power supply and the step up transformer ran a bit hot which I wasn't a big fan of. This new power supply runs on 120V of course and runs quite a bit cooler. Plus it physically takes up less space (one unit versus two).

Other then that, I've been toying about with AMOS here and there. It's been fun, and a real blast to the past for me which I'm enjoying so far. Not much to say other then that yet really, as I've just been continuing to work through the user guide for an hour or two each night, as well as consulting some other books I've picked up as I go along while learning the ins-and-outs of the hardware. Once I finish up going through the user guide (which is fairly thick, almost 400 pages), I'm thinking I may start with a vertical scrolling 'shmup type of game just to get my feet wet. It'll probably take awhile to get going as it'll obviously be my first AMOS project. Overall though I'm finding AMOS easy to get into. I think what will be difficult at first is optimizing for the limited hardware. And that's the challenge I was after in the first place.