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Digital 54-22703-01 Motherboard – L2 Cache

After making this motherboard fit into the IBM PS55/z, I realised I hadn't decked it out fully. I'd mentioned cache in the first post, and finally got around to ordering some. The goal was to speed up the poor old 486 as it wasn't running as fast as I would've expected it to. Of course, this was also all very subjected as it'd be pretty impossible to actually remember how fast my first PC actually ran!

Usually, parts like this can be pilfered from other items laying on the shelves in my apartment, but this motherboard needed specific 'TAG' RAM, as well as the standard 32KBx8 static RAM chips. I had to go hunting...

Required components

Back to Pafe 45 of the User Manual for this motherboard and we find that we need eight 32 KB x 8 cache SRAM chips and three 16 KB x 4 cache tag SRAM chips to max it out. Straight to eBay and I found a seller in Israel with the correct parts. I incorrectly ordered two sets of TAG RAM chips and only half the required static RAM chips... whoops... fortunately I could pilfer those off another board!

The TAG RAM chips are labelled MCM6290BP25 RIQAB9131.

As per usual... always be careful when inserting ICs. Make sure their legs are aligned with the sockets and don't press until it's safe... otherwise this happens!

With everything in, we just need to adjust the jumpers...

Set all four jumpers (J3,J4,J6,J7) to 2-3... and then boot!

Yosh!

Test Software

Go here and download anything that starts with Cache. I then tested them all out...

They all showed that any data size under 256kb proved quick response times. The rest started spiking as more operations were required. The CCT386 application had awesome graphs.

Now to work out if the games actually operate faster...

Microchannel Sounds Cards (aka Hen’s Teeth)

I was interested in these when the IBM PS/55z was on its way as I wanted to deck the machine out with sound. Turns out that MCA is a rare breed and actually-interesting cards are impossible to come by.

Imagine my surprise when I saw an MCA ChipChat Sound Card (with wavetable addon!) appear on eBay. It started at AUD$50 and I was interested... just because it had to be an investment to sell later?

Here's the description...

This a ChipChat Sound-32 Card for a IBM PS/2 Microchannel computer.
It comes with original box and contents. Including reference disk and driver disk.
Drivers are for DOS, Win (3.1, 95, NT), OS/2 (2.x, Warp)

And a few pictures:

So yeah, nothing special... not even a mention if it works? Anyway... the 7 days were nearly over and it had gotten up to AUD$141. I was a little disjointed, but yeah... it's a relic! I mean, it's beautiful.. but... I wasn't expecting the outcome:

I'm very happy that someone, who I hope REALLY REALLY wanted it, got a very nice piece of computing history!

Testing EGA/CGA Cards

I'd picked these up a while back but never thought I'd get to test them. I don't have any monitors that support the old standard and haven't actually seen any available on eBay for a long time. I was quite surprised when I realised that the GBS-8200 that I picked up for my MSX would work to convert the frequencies! I'd only ever expected to use it for the MSX RGB signal.

V7 VEGA 8-BIT VGA

This card (thanks, stason.org!) has the ability to output both EGA/CGA and VGA! It's 8-Bit ISA and it a little worse-for-wear...

This seems to be quite an advanced card of its era. Happily outputting to the monitor you happen to have and allowing for future upgrades! It also even seems to have the VGA auxiliary header?

VIDEO SEVEN V7 VEGA EGA

This card (thanks again to stason.org!) is a little older. It has a header for a light-pen and suppsoedly two composite video inputs!?

GBS-8200

I had purchased the bare-bones board and never tried it. Thanks to my new desktop power supply, getting it going was really very easy. The board comes with a standard DC jack, but also a pin header for the input voltage. Instead of using a crappy wall-wart, I instead powered it on the supply, having the additional benefit of knowing the current requirement!

Ian Stedman thoroughly reviewed this board. His outcome was that there were a few issues, but a strong power supply is not needed. It turns out that my testing below shows that it hardly needs 5v at 400mA!

You can see where I've soldered on to for the EGA/CGA input. It's the bottom-right 5-pin header and I couldn't find an acceptable plug. In the end, a quick bit of tinning worked. There's 4 wires: R,G,B, Sync and Ground. The EGA Pinout on Wikipedia (CGA is nearly identical) shows that there are two sync lines, but we only have one on the GBS-8200! As mentioned above, we'll use the bottom-left connector on the board.

Combining HSync and VSync

We'll need to combine the Horizontal and Vertical Sync outputs from the EGA signal as the GBS-8200 requires a single Composite Sync signal. To do this, we can use an XOR or OR gate. Ian is our saviour once again and has provided a circuit to combine the signals.

Build the circuit as he's described. I actually found that either XOR or OR worked fine with the GBS-8200!

I probably should've tested some games...

Hercules?

No such love. Same connector, but a very different video signal. Turns out it's actually a digital TTL signal that this unit cannot process. If you really want yo convert it then you'll need to buy a GBS8219.

Is that a printer port? Space saving tech! I don't have any plans to pay for a Hercules monitor or an 8219, so this is going straight on eBay.

DOS USB CD Drives? Of course!

After mucking around trying for a while trying to get the new Compaq motherboard into the old IBM PS55/Z, I realised I'd wasted a lot of time playing with SCSI cards. This motherboard has a USB port! Can I use an external USB CD drive in DOS? It turns out the answer is yes!

Download USBASPI.SYS from here and then a USBCD.SYS (choose your brand) from here. I fluked it and tried the first USBCD1.SYS driver which worked perfectly! Firstly, copy the files to your HDD (I always put them in C:\DOS\), and then edit CONFIG.SYS:

DEVICE=C:\DOS\USBASPI.SYS
DEVICE=C:\DOS\USBCD.SYS /D:MSCD001

And don't forget AUTOEXEC.BAT as follows:

C:\DOS\MSCDEX.EXE /D:MSCD001

And reboot...

Out with the old and in with the new!

Meanwhile, Windows 98se kept locking up (whole machine freeze!) at Programs on the Start Menu. I actually had to unplug the CD drive and reboot to get it to continue! But the end result was lovely...

Time to really make this motherboard fit!

IBM PS/55 Z – All About The Pentiums

Found this at the local flea market on the weekend. After spending many nights replacing the guts of my IBM PS/55Z with a 486 DX2/66, I saw the specifications of this motherboard and couldn't resist snatching it up. 166mhz! PCI! ATX! 96mb RAM! USB! What more could you ask for in a vintage machine? I wonder if I should try and make it fit!?

Turns out it's the motherboard from a Compaq Deskpro 2000. Am I happy to have the Compaq splash screen display when the machine powers up? I believe the BIOS will also be tricky to get into as these machines need a separate hidden partition with Compaq's proprietary tools?

A quick Google lead me to realise that building an AT to ATX adapter would be a nightmare. I'd need to create a solid +3.3v DC supply from the 5v rails and also muck around with more sense wires? Might be easier to just rip out the power supply and slap an ATX unit in there. Would have to merge in the CRT electronics though... Of course, it's also ever-slightly too long, so there'd need to be quite a bit of hacking to make it fit.

Such delight at finding this beautiful piece of equipment! ... Oh wait, maybe this will be easier than expected!

How To Actually Connect An External MIDI Device

I started this journey thinking that MIDI cables were really simple. There's a joystick-style plug at one end and two DIN-5s at the other for MIDI-OUT and MIDI-IN. MIDI output from the computer comes out the OUT cable and MIDI you're receiving from elsewhere comes into the computer on the IN cable.

So, when you're hooking up an external module, like this MT-100, you simply connect them up...

There they go, OUT to IN and IN to OUT. Right? You want the output from the PC (be that the soundtrack of a game) to go into the Synth/Module to be processed. Like so... I don't really care about the module output at this point, but for-neatness-sake, let's plug it in!

IT TURNS OUT YOU DON'T WANT TO DO THIS. You're actually creating a loop and the MIDI data will come straight back out of the module and into the PC. This will then cause all matter of DMA/IRQ interrupts and you'll probably freeze your machine. I've actually just spent the greater part of two nights having DOOM II lock up every time I set both SB16 and MIDI-OUT. I went through all matter of IRQ or DMA settings, thinking the combination of a SCSI card, Network card and Sound card were fighting. After a quick google of vogons, I realised that the machine was freezing/slowing-down/locking-up due to the rebounding MIDI data!

This article was actually going to be titled 'DOOM II Freezes when selecting SB16 and MIDI-OUT'. Either way, do this instead... connect OUT (from the PC) to IN (on the module)...

And you'll be an uncle's monkey!

Ahhh… Floppies

There's nothing like the smell from a fresh box of floppies. That acrid plastic fragrance, reminding you how technologically advanced these little wonders are...

I recently found this box for a dollar at a local tip shop. Over the moon, I thought I could finally build a solid set of DOS 6.22 and other disks. I even got labels! Of differing colours!

Of course... none of them worked... They'd neither be read, formatted or imaged. I assume that fresh smell of acrid plastic meant that these had all been toasted by the sun at some point.

In the bin they go... Or maybe I should make some art.

IBM PS/55 Z – Replacing the Guts

I was unsuccessful in restoring the original motherboard contained in the IBM PS/55 Z – 5530 that I picked up recently, so the new goal was to find a similar motherboard with riser card and give the machine an upgrade. I knew I'd never find an exact fit, so I started preparing to make things work.

The overall structure

The motherboard in this machine is around 290mm x 340mm and has a central riser card with 3 MCA slots. These are slimmer than ISA cards, so there was always going to be an issue fitting a standard riser card in there. There was also only front-panel space for two 'tall' floppy drives and hardly any other room internally for hard drives.

Digital 54-22703-01 Motherboard

This item popped up on eBay and looked like a perfect fit. It had no RAM and a Dallas CMOS chip, but I'm always up for a challenge. The board happened to be smaller than the IBM board and so there'd be extra effort to mount it, but it had a replaceable CPU and I had an upgrade for the stock DX-33.

At first it didn't even want to boot. The front-panel connector is a pin-header and I have no idea of the pinout. Flying blind, I tried just about every RAM SIMM I had and still couldn't get it going. Finally I remembered I had an ISA diagnostics card, of which I'd never tested.

Once plugged in, I kept getting 0xD0 on the display... oh wait... that's 0x09. The manual indicates that it's failing to read the stored CMOS configuration data for the BIOS. Well, that isn't entirely unexpected as the Dallas clock-chip is probably toast. I quickly fixed this, as I've done before and before.

With this in, it still didn't work. I emailed the eBay seller as they'd hinted the board needed specific RAM. He sent a few pics of SIMMs he thought might work and I scrummaged through my box-o-junk and found similar. With a little more swapping and testing I got the card through to 0x57. Interesting... nothing on the screen.... OH! I'd disabled the on-board VGA whilst testing!

After a little more testing, I found 3 4mb SIMMs, totalling me up to 12mb of RAM. Perfect for a vintage 486 DX2/66. Note that the board still uses a 33mhz clock when running the DX/2 66mhz. As per the board configuration, the 66mhz is 'internal' to the CPU!

Mounting it

The chassis is pure steel. It took a lot of bending, twisting and grinding to make this fit. The bottom rear slot needed to be extended and the base was punched to allow mounting screws for the motherboard. I then created a vertical bracket to secure the ISA cards to. Thankfully this board had on-board VGA... otherwise I'd have totally run out of slots!

The middle riser card that came with the board was too low... the bottom slot was too low. Fortunately I had another riser that worked perfectly. The lower riser also didn't clear the clock-mod I did for the cell battery!

The plastic housing for the hard drives and floppies was a bit of a pain. It used to secure the center riser card and this was no longer an option. It also held the front floppy drive with very little clearance from the motherboard. I chose to swap the floppy to the other side, but this caused even more problems as the actual case had a blank panel there! More dismantling saw this to be an easy swap, but not after a LOT of fiddling.

As you can see above, I'm messy and always in a rush. Regardless, the end result was totally functional.

Power Supply

The previous motherboard had an edge connector with voltages supplied from the power supply in the chassis up top with the monitor circuitry. This was based off 110v, as the unit was from Japan. I wanted to change this to a newer power supply... so I dismantled the monitor to determine if it was even possible.

All was looking good until I saw that one of the wires over to the monitor board needed +85v. I've no idea how to generate that from a standard PC power supply... so I went back to the original idea of augmenting the internal power board to work with an AT motherboard.

After analysing the pins, I started the re-routing. All was available except the -5v. Goshdarn. I tried to boot it anyway and got a 'blip' from the SCSI LED... but no POST. How do you generate -5v? Seems you can use an oscillator circuit or an LM7905. The guess was that I could use the -12v rail to provide a -5v rail.

A quick soldered-up hack got the -5v rail in place and, well, it booted??? I couldn't actually believe my eyes...

I then turned the power switch off and back on again. I then had issues getting the machine to reliably come back on. Seems that I'd fluked it this time around and the -5v rail wasn't the answer.

Power Good

Seems that the very first pin of a standard AT Power Supply is known as the Power Good signal. This line goes high (+5v) when the power supply has decided it is outputting valid power values and that then notifies the motherboard to start booting. The main point to note in that article is that a motherboard will reject this signal if it fires before 100ms and after 500ms. Eep... we're tied to 5v, so it's probably either totally noisy or easily firing before 100ms.

So... do I fully review the power board in this system and determine a proper value for this? Or just hack in a fake timer to produce a 200ms delay? It seems that we're already causing a random delay on the line as I can get the machine to boot sometimes... so I might just try and fake the signal by use an RC charging circuit to add a small delay.

A quick interesting note: I actually used the wiring off an old power supply from a dead power macintosh for the motherboard plugs. It turns out that pin 1 and 6 were tied together by a tiny capacitor!? That capacitor is shown above. It seems Apple were using the same trick on their 7220 line of Power Macs. Might've been a cheap way to use pc-specification power supplies in that model/series as the goal back then was to be as off-the-shelf as possible to produce a cheaper line of macs.

Anyway, where was I? Oh yeah... I want to fake the signal as well. To do this, I'll throw an electrolytic capacitor and resistor onto the power good signal wire. Use the calculator here (thanks Digikey!) to determine what you need. We'll want a 200ms delay from a 5v supply, so that's a 2k resistor and a 100uf capacitor. The resistor will be between the 5v supply and the positive terminal on the capacitor. We'll then connect the other side of the capacitor to a ground line. Finally we'll run the power good signal wire to the join between the capacitor and the resistor.

Turns out my trusty box-o-stuff only contained 3k3 resistors, so I soldered in this and an 100uf electrolytic capacitor and, heavens above, the machine booted everytime without fail! I then used the remaining 12v and 5v wires to get both full-size and floppy-size molex power plugs connected. Make sure you get the power wires the correct way around! Before I knew it, the machine was booting without any external support. Unfortunately it was stalling at the SCSI BIOS.

HDD Sizes

The BIOS in this machine was determined to not let me use the full size of my 1.2gb C:. I attempted to use ANYDRIVE, but it really didn't like the GOTEK that I was using. Instead I gave EZ-Drive from Western Digital a shot. (Really good VOGONs thread on the topic here!)

I also considered tinkering with the actual BIOS of the motherboard. It seems to be two EPROMs and I would've been happy to whip out an old machine with a real LPT1 port to program one. A little digging revealed a great archived site with the DEC LPV+ support files. One of them even mentions the drive size limitations I was facing! Hah... it then simply recommends to use drive overlay software... So, back to EZ-Drive...

Firstly, set up your BIOS with the 'default' setting for a 504mb drive.

Next, download the EXE (not the ZIP) from Phil's Computer Lab and copy it to a disk. I was using a Gotek, so I copied it to one of the blank disks available. Boot using another disk and then switch back to this one. When you run the EXE, you'll be greeted by the welcome message. It'll take some time at this point as it's copying itself to RAM. Once in RAM, it'll inform you that it's time to switch disks. At this point you need to insert a blank disk that'll be your EZ-Drive boot disk. I swapped to a new slot on the Gotek and hit enter... in no time the disk was built and I was prompted to restart.

From here, it's child's play! The GUI is perfect and found all the information it needed. I just kept choosing the default options. During the install it'll ask for a disk with a bootloader on it. I switched the Gotek back to DOS 6.22 Disk 1 and it copied the required files over.

Once complete, the machine will actually boot from this drive to the basic DOS it installs. Unfortunately, DOS still needs to be fully installed and cannot be done from the booted HDD as the floppy will tell you to restart with the disk in A:. Of course, if we did this and booted straight from the floppy then we'd undo all the work that EZ-Drive has just done. Instead, as per the instructions below, we need to try and boot the HDD, but hit CTRL just as it's about to start.

If your timing is good, then you'll get the following screen...

From here you can hit A, get the disk in the drive (if you have a Gotek, then wait 2 seconds after selecting the floppy index number!) and then hit any key to boot the disk. DOS 6.22 then installed with a minor warning that it'd overwrite the current DOS install... it's not a real DOS install (it was just the boot files that EZ-Drive copied over), so yes, please, wipe it and get my OS ready!

Meanwhile, if you're adventurous... there's a truckload of DDO software here to try out if you can't win with ANYDRIVE or EZ-Drive.

SCSI Card

The card is an Adaptec AHA-1542B and it really didn't want to find the attached drives. I had an external case with a CD drive and an ultra-wide (converted to 50-pin) 9.2gb IBM HDD.

I could see it pinging both drives, but the card never seemed to find Drive ID 0 at LUN 0 whilst loading the BIOS. Usually you can hit CTRL-A at this point to get into the BIOS configuration, but this card wasn't even offering that option?

There's a mention on this forum post that my card can only do up to 1gb HDDs. The manufacturer reckons that it will support 8gb drives. Unfortunately, I don't seem to have any drives small enough? Maybe this is why the boot is stalling. The AHA-1542C BIOS ROM is here, but probably wont work in this card. There's AHA-1542B BIOS ROMs over here on Github, but a quick Notepad++ inspection of the BD00 bin image shows that the newest one is already version 3.20... I have 3.10 so maybe I should update?

I'd been testing all this on an ultra-scsi hdd with a converter... but I remembered I had an ancient macintosh 1.2gb drive laying around and it was a proper 50-pin! It worked perfectly... and then I remembered that old MOTOR START trick. These server-grade SCSI HDDs don't actually spin up until they're told to. Usually you can request this under options in the SCSI BIOS, but this card doesn't seem to have one! Instead, I had to adjust the jumpers on the drive itself AND the converter/adapter. Note that these drives, with only power applied and the MOTOR jumper set, will spin up. Once you plug the SCSI cable in, regardless of the MOTOR jumper setting, they WON'T spin up until the host has been turned on!

All of my SCSI devices were mounted in an external case and it was causing me grief. As mentioned, the drive would spin up fine with the jumpers set and power applied, but as soon as I mounted them and closed the case, a quick power-on test would see the HDD no longer spin up by itself! I spent a long time trying to work out this out. As mentioned above, the result is that the drive won't spin up if an actual ribbon cable is plugged into the drive. The MOTOR will only spin up when it senses that the host is switched on. So the MOTOR jumper is really I'LL SPIN UP IF I SEE THE HOST IS ALIVE; I assumed it was I'LL SPIN UP IF I HAVE POWER.

With everything now powering up, the BIOS was listing the drive as D:. I then tried the ADAPTEC DOS Drivers and found that ASPI4DOS.SYS 3.36 just kept reporting Installation Failed. I found a forum post on VOGONs that mentioned a version downgrade to get things working. I love little hints like this: ASPI4DOS.SYS 3.35 worked perfectly! Of course, 3.36 has all the disk tools whereas 3.35 is just the drivers... I had to download and put both on C: to be able to get the SCSI drive into a usable format.

With partition size limitations, I made 3 that were around the same size as C:. D: was still only being mounted... but I assumed Windows would find the rest. Note that, if you've mounted your D: via the SCSI BIOS, you will be limited by your computer's BIOS for partition sizes. I recommend NOT mounting via your BIOS first and booting to DOS to use AFDISK from the 3.36 driver archive. Once you've created your partition set, you can then turn the BIOS back on, or just let Windows use the drives and have DOS forget them.

Sound Card + MIDI + Speakers

I had an ISA sound card sitting on the shelf. It turns out it's a Reveal SC400 Rev.3 (I38-MMSN811) which seems to have come from a Packard Bell system. Further digging indicates that this card is actually just a rebranded clone of a third generation Sound Galaxy Nova 16. It utilises the AZT-2316 chipset and you can find more information about the whole family here. Grab the full Aztec Driver kit here, and make images of the first three disks in the NOV16E folder. I couldn't actually get the DIAGNOSE application to work successfully... it seemed to either hate the DMA or IRQ configuration... but running DEMO8 and DEMOFM produced sound!

Of course, if you're going to use Windows, then everything will just work. This card is new enough to be well-supported. That bloody W95 Chimes and TADA! were playing over and over whilst installing software and restarting.

Networking

This was the easiest LAN card I've ever installed, well the easiest ISA LAN card. It's a 3Com EtherLink III 3c509b. No jumpers, capable of PnP! Of course, that wont work here, but Win95b happily configured it.

Under older windows, don't forget to provide the gateway and DNS settings! These won't be auto-discovered from DHCP. Internet Explorer 3.0 actually just worked perfectly. HTTPS sites all failed... which is actually a really big issue now with older hardware. Thanks to all the new HTTPS security requirements, no older software works with new URLs.

Front Panel Connection

The DEC obviously had a proprietary front panel board. The header on the motherboard was unlabeled and there is zero documentation online. I grabbed my trusty multimeter and started probing the wires for voltages.

The hard drive activity light was found by choosing the biggest folder on C: and copying it to another folder. From there, there was only one pin that was 'pulsing'. I wired this through to the LED on the front of the IBM. The speaker was a little more tricky. I created a quick QBASIC program: 10 BEEP; 20 SLEEP 1; 30 GOTO 10; which happily started a 1 second beep every second second. Again, this rhythmic pulse was found on another pin. Each seemingly had a GND as a neighbour... but maybe I should have hard-wired to a real GND as I don't know if the neighbour wasn't another digital signal?

Windows

This was going to be another WFW311 machine before I realised I was easily spec'd for 95B. Back in the day, the family had a 486 DX2/66 with 4MB of RAM and we went to the computer store to get a bigger HDD and an extra 4MB of RAM for Windows 95! This machine has a MUCH bigger HDD and 12MB of RAM... so we're good to go.

A quick visit to my favourite site produced the required install media and the WIN95 folder was copied to C:\. I always do this as it makes it much easier when configuring (or re-configuring) network options in the future. Windows always manages to ask for the Installation CD and if it's on C:\ then it just zooms through without asking.

The installation was nearly painless. After typing SETUP.EXE, I was stuck just after hitting ENTER to scan disks. Scandisk didn't actually come up and the SCSI drive was making a very noisy hum. Turns out the heads were starting to fail and SCANDISK's attempt to wake up the drive locked up the computer. Well, not the whole computer... turning off the external SCSI enclosure saw SCANDISK continue... but that wasn't acceptable. I quickly swapped out to another SCSI drive (and partitioned and formatted...) and started the install again.

Before I knew it, I was at that treasured desktop once again! Here's Opera 6.00 and WinZip 5.0.

1024x768 Resolution

The Display Adapter IV card in the old mainboard was capable of a 1024x768 resolution. Unfortunately, this had a weird mode and wasn't standard SVGA. The display mode is detailed here (thank you, Diary on wind) and I tested out if Scitech Display Doctor would make Windows 95 display it. Turns out that previous link is shit.. use this one instead. (or here) (or here) You can find PMHELP.VXD here.

Here's the Quadtel DEC VLB S3 805 Driver.

It turns out that, even with the relevant display drivers installed, Scitech just doesn't care for my video card. The video is soldered onto the motherboard, so we're out of luck. I'll try and find a monitor INF for the display or something shortly... there must be other methods!

L1/L2 Cache

Windows 95B performed pretty awfully... or maybe it was Scitech Display Doctor that started to make it chug... either way, I wanted to see if I could boost performance. One standard method is to install cache. This is a small block of RAM that sits right next to the CPU and provides a 'working area' to pre-load the next disk or ram segment so it's readily available. It's actually the reason the newest CPUs on the market have security bugs as the data pre-loaded can be from other applications and then be viewed.

For this motherboard, there's 8 RAM slots and 3 TAG RAM slots? Page 45 of the Service Manual indicates that I need For the DECpc LPv, secondary cache memory consists of four or eight 32 KB x 8 cache SRAM chips and three 16 KB x 4 cache tag SRAM chips. I jumped on google to try and find the TAG RAM chips, as all boards I already had only had the cache chips.

I hadn't actually heard of TAG RAM before and didn't exactly know what to look for. It turns out it's a block of RAM used to store address data of what's actually in the cache. The CPU uses it to bookmark where it's at and what data is where. For this we'll need 3 chips of 16KBx4. These all seem to be in Israel, so I'll sit tight and wait for them to arrive.

Update: Cache has been installed!

The Final Product

Getting this thing running was a real tour-de-force. At no point was a single task easy, but for the first time in a long time everything did come together nicely. I'm really happy with the end result and may just leave this as my beige beast for playing old games!

IBM PS/55 Z – 5530 All-In-One

I saw this on eBay and couldn't resist... I probably should have resisted... I also probably should have actually reviewed the specifications prior... but whatever... I made the seller drop it to a Pack'n'Send and it arrived, perfectly packed, in no time. It's a cute little unit. I actually had the 12" IBM VGA monitor back in the day as a single unit and loved it for its clear and sharp 640x480 picture!

The IBM Personal System/55 (Here's some more information) was a series of computers released in Japan back in the late 1980s. It was based on the x86 architecure, but used IBM's own Microchannel (MCA) system bus. I sorta wish I'd researched that point beforehand as nowadays MCA cards are few and limited in technology. Ethernet is hardly BNC co-axial and SCSI is rare. Audio is even rarer... but there were Creative and Roland cards! Good luck trying to find one!

The front sports two slots for floppy drives, brightness/contrast and a lovely lever-style power switch. There's also your power and HDD LEDs. The swivel base is also a nice addition. There's even a lever on the rear to secure the unit once you've swivelled it to the point you like.

There's a panel on the rear to cover up the VGA cable. This cable is a little strange... it seems to be an artifact from the fact that the whole unit is really just an IBM 12" monitor with a growth hanging from the base. Instead of running the cable internally, they actually have a midget lead and plug that is exactly the length required to fit into the Display Adapter card which can therefore only be in slot one. This becomes more apparent inside when you realise the card requires an extended slot and, you guessed it, slot one is the only such slot.

The whole PC area of the unit slides out once you unplug the VGA cable and unscrew the two black screws. I really do like the modular design! Note, it also seems this unit expects the keyboard to have a speaker in it? Interesting!

But what does it look like on the inside?

Getting access to the motherboard is super easy. Unscrew the two screws and then slide the whole lot out. Make sure you unplug the VGA lead first! The shelf that the motherboard sits on is easy to work with and provides access to drives as well. My unit didn't come with any... I assume the floppy will be standard? But the HDD definitely isn't. Jeesh. The MCA bus is also totally obsure and the graphics card is a Display Adapter IV. It also needs to stay in the top slot as that's the only extended MCA slot and it's also the only one the VGA lead will reach to.

You'll note that with the motherboard removed, the case is still very much in-tact. Actually, it's sealed. Getting to the area where actual power supply and monitor are is a little more tricky. I wanted to give it a good visual inspection prior to powering up, so I endeavoured to open it. Turns out it's built to be totally tamper-proof and return-to-factory only! There are two removeable caps on top that present you with 'headless' screws. Yes, they're screws... but there's no ability to actually unscrew them.

I made a total mess with my (fake) dremel to try and gouge a flat-head screwdriver slot. I ended up melting a lot of plastic... but for some reason I'd decided that the covers will go back over, so the mess is contained. Either way, the screws came out and the case came off.

Yup, it's a CRT alright... and that power supply is totally embedded into the monitor housing. So much for an easy switch to a 240v supply. I'll revisit this once I work out if the motherboard is good. If it's not, I might just gut the whole thing. Back in '99, The Techtroid Box did just that.

Meanwhile, the patterns of dust on the inside of the monitor housing were slightly mesmerising!

Motherboard Layout

This is a flat AT style board. All integrated ports are along the rear. Some of the ICs have IBMs infamous heatsink shields that make them look military-grade. The MCA bus is obvious and two riser cards exist for a HDD and the 3 MCA slots. There's also a floppy header and some random jumpers.

There's a header at the top end that plugs into a socket very similar to a Commodore 64 User Port Edge Connector. This is fed from the powersupply that's intertwined with the monitor circuitry in the do-not-touch zone. Looking down at the board, with the edge connector pointing up, the pinout seems to be as follows:

		GND	GND	GND	GND	GND	GND	GND
-12v	12v	2.8v	5v	5v	5v	5v	5v	5v

So, above you'll find the top and bottom rows, as if you were looking into the socket inside the chassis from the rear. I have no idea if the voltages are correct as my machine isn't booting.

Does it work?

The unit requires 110v AC, so I used my trusty step-down transformer. After re-assembling the bare minimum, I applied power. The monitor came to life, but the motherboard was dead. There was a little bit of heat from the CPU, but no other life. No manner of RAM SIMMs helped. A closer inspection revealed that just about every aluminium electrolytic capacitor had started to corrode. Tracks were beaten in a few areas. Looking even closer, it also seems that the motherboard is 4-layer: tracks top and bottom with two plates in the middle... possibly positive and negative?

I started replacing capacitors where relevant and testing tracks... No amount of effort brought it back to life though.

Turns out you can feed the motherboard connector through the front floppy slot and then connect it up... allows for much easier fault diagnosis!

Is it the EPROMs?

I intend on popping them out and reading the data off them. From a visual inspection of the code, I might be able to tell if they look OK? Maybe copyright data, etc... but I'll have no checksum to work with to determine if the images are correct. I'll also have no other images to load to test further...

Final answer: replace the guts?

I'll do this in another post. There's a few options for motherboards with riser cards on eBay and I'll need to choose wisely as I'll want the measurements to line up as closely as possible. Of course, I could just slap something in (as per The Techtroid Box's post), but I want it to be cleaner and more permanent.

Does the CRT work?

The video card is an IBM "Display Adapter IV". Supposedly it has an 1024x768 mode? Here's more information, albeit in the wrong language. And this article (scroll down to PC # 6) also indicates the resolution.

I happily got 640x480 working... I'll spend a little more time later with 1024x768. First I'll find it some new innards.

68-pin RAM SIMMs

I had previously picked up this Bravo 4/33 486 Machine and had assumed, from the photos in the auction, that it needed standard 72-pin SIMMs. A quick physical test proved this assumption very wrong. This was a proprietary motherboard and the slots were narrower than 72-pin SIMMs and wider than 30-pin! I'd never actually seen anything like this before. I then researched and realised that this board needed 68-pin SIMMs.

eBay came to the rescue and two 4MB SIMMs arrived from Denmark! Seems they're mainly used in Roland hardware or Macintoshes. Anyway, from the photo above you would easily mistake them for 72-pin SIMMs. It all becomes obviously when you line up all the types...

Above we have a 128-pin SIMM, a 72-pin SIMM, two 68-pin SIMMs and then a 30pin SIMM. I think quickly tested in the motherboard and success! They fit!

Of course, the machine still didn't boot... time for more mucking around... (and no, it wasn't the fault of that loose screw...)