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Compaq Deskpro 386s/20n: CMOS Battery

So, I totalled the previous motherboard and found a new one online. This one was the 16mhz version (the original was an SX-20) and had a different component layout. At the same time, I also purchased 8mb of RAM (Parity SIMMs!) and a 'new' Dallas Clock Chip/Battery from eBay.

After slapping it all together, the RAM counted up nicely and I could get into the setup as per usual. I configured the HDDs and then saved the settings and rebooted. Instead of working fine, each reboot presented me with the 162-System Options Not Set-(Run Setup) error. No amount of configuration would work. Everytime I continued and went into the setup, it would remove the HDD configuration. I could see that the BIOS wasn't even searching for the HDDs.

This was weird as the system was more-or-less configured back to a standard Compaq factory-issue. Everything was in good nick. I had a hunch though; maybe that Dallas Clock Chip from eBay was actually already dead!? The fact that I hadn't powered down the system meant that the configuration should have applied; this didn't seem to be the case!


I replaced the battery as per the previous one that I replaced (I actually ended up using the original one on the motherboard for the other 386 I picked up recently.) With the hack in place, the BIOS configuration saved and the HDDs were detected and ... the world was a happier place!

So... if you have a dodgy old Compaq Deskpro like mine: MAKE SURE YOU HAVE A GOOD CMOS BATTERY!


Compaq Deskpro 386s/20n: Onboard VGA

This machine only has two ISA slots available, so options are immediately limited for anyone who wants sound, network and upgraded video! Currently the machine is running (what I believe) is a better spec VGA card and a Crystal sound card. I wanted to also try a network card, so I have endeavoured to get the onboard VGA working.

Rear plug - blocked pin?

The port is there, but back in the day they blocked pins so that you could only really plug in Compaq monitors. I don't know if this was to make sure that you gave money to Compaq, or if they were worried about monitor compatibility.


Either way, I now had to either destroy a VGA cable or build an adapter... I chose the latter.

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The adapter was simple... just don't connect the blocked-out ground pin. It didn't work... well, it did, the adapter worked fine on the add-on VGA card. Once plugged in to the on-board VGA, with dipswitches set and the add-on removed the machine just didn't boot. No beeps, nothing.

Motherboard dipswitches

These are pretty simple. Smush in the top side to set them to 'ON', the bottom side for 'OFF'.


As per the instructions.


I love it that it says 286N. Silly Compaq... re-using old cases for new hardware.

No dice

Maybe that 'X' above the port was put there when the onboard video failed decades ago? I've no idea when, but it doesn't work. Hence why the owner bought an add-on video card? What are my options here?


I straightened the pins that you see bent above, but that didn't work... I was a little sad... I wanted two ISA cards in there. This board could nearly be considered a total loss if it was partially-working. I have no real way of determining what else could be malfunctioning.

Maybe I should 'reflow' the board as described in the process here?

Reflowing, what could go wrong?

I killed it. I totally killed the motherboard. DO NOT REFLOW OLD ELECTRONICS. But this is what it looks like anyway... Bake away, pretty motherboard.


The idea is that, by heating the board to 200 degrees celsius, you'll re-connect all the solder joints that have aged badly. I hardly put the thing in the oven for a few minutes (less than 5) but it stopped working afterwards. Turns out that the board uses tiny solder joints to connect the top layer to the bottom layer and most of these succumbed to gravity. None of my efforts to re-connect these solder connections worked.

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I managed to re-seat that PLCC socket and replaced all the electrolytic caps that were bulging... gah. I assume I've done massive internal damage to the ICs though. Meanwhile, the little motherboard top-layer to bottom-layer solder joints are all stuffed.


Anything above or below that looks like a solder ball sitting on top of a hole in the board shouldn't be there. Above is the underside of the board and the solder has dropped out of the hole and is hanging in a nice sphere. If you look closely, and I apologise for the focus, you'll see 3 spheres, just below the right-hand-side of the edge connector. They shouldn't be there.

Below, if you see holes resembling black-heads then you'll realise that there should actually be a nice flush bit of solder there!


I attempted to re-solder with my soldering iron... but a lot of the joints just wouldn't accept the solder... I'll store this board, I'm not accepting defeat just yet... but I'll need a solder-sucker and a higher quality iron to get it going again. If the ICs are dead. Meanwhile, another motherboard is on its way.

Maybe I should put it back in, upside down?



Compaq Deskpro 386s/20n: More RAM

This has been a challenge. The user manual only really indicates the spare-part numbers for modules, but searching for those proved difficult. Therefore I went in for the lucky dip and purchased whatever I could find on eBay.


First was a cheap batch of unknown SIMMs. They all turned out not to work. I then purchased 2x4mb EDO SIMMs specifically by Compaq, but they didn't work either. There's a few FPM SIMMs below that should work... maybe they've been damaged by static or are of the wrong spec. Seems like I need compaq-certified FPM and hopefully I've now ordered the right parts.

Here's what I've got, what worked and what didn't. I've used the DRAM info page at retro hardware to try and determine the module information.

Update: There's a link here at efetcher that indicates I need parity RAM.

Module details Chip details Status
Original 2mb SIMM
(256kbit x 4) x 16 = 1mbit x 16 = 8MB x 2 = 2mbyte
KM44C256BJ-8 (x16)
KM41C256J-8 (x8)
Works - 2mb
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Compaq 2x4mb EDO SIMMs Compaq 185173-002 - EDO - 4MB
Fujitsu 814405C - 60
9269 F98 (8 chips)
Does not work
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Could be SMART CQ SM5321000W-7
1mbit x 16 = 2mbyte x 2 chips = 4MB
JC - 70
9545A KOREA (2 chips)
Does not work
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4MB DRAM Singapore TM248GBK32U-60 9706
TM5418169DX (4 chips)
Does not work
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4M bit dynamic RAM organized 1,048,576 x 4-bit
4mbit x 8 chips = 8mbit (1MB) x 4 chips = 4MB
Maybe EDO?
J - 70
9512B KOREA (8 chips)
Does not work
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Another 4MB FPM?
ABORL1 - 6 (8 chips)
Does not work
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4M bit dynamic RAM organized 1,048,576 x 4-bit
Officially EDO.
16 chips = 8mb.
SEIWA - Made in Japan
LJ - 60
9461C KOREA (16 chips)
Does not work
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4M bit dynamic RAM organized 1,048,576 x 4-bit
Officially EDO.
16 chips = 8mb.
4mb 72-pinn PARITY SIMMs WORKS! - 8mb
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The machine simply does not turn on when it doesn't like the RAM... no beeping, nothing. Will report back when the FPM parity RAM arrives.


Compaq Deskpro 386s/20n: Running 386BSD

I've wanted to run *NIX on my Compaq Deskpro 386s/20n and I've just stumbled across the perfect distribution for it. Turns out that, back in teh mid-90s, a bunch of developers created 386BSD based on 4.3 BSD. The source of 386BSD 2.0 has recently been released and is now available via the 386BSD github repo.

I'm not overly confident with raw *NIX systems, and so was hoping for a boot disk/installer scenario and it seems that this is provided. Below are my feeble attempts to get it going.

Creating a boot disk on Windows 10

For most of the following, I've used the instructions found here at for getting 386BSD running on Qemu. I downloaded rawwritewin. dist.fs was written to the disk, but it failed in every system I tried it in. Turns out it's a 1.2mb image and not a 1.44mb image. Somehow the tracks/sectors of the floppy are written into the image and incompatible when you write them to a disk of differing geometry.

I then searched, trying to work out how to convert a disk image from 1.2mb to 1.44mb. The link above just pads out the image file with zeros... but this can't be correct? Seems that QEMU will happily boot that though? I then came across this link which uses ImageEdit to convert a 1.2mb image to an IMD. This app doesn't run on Windows 10, so I booted up my Win98se VM and ran it there. An IMD was produced, but this had the same issues on all disk writing applications I tried. You can download ImageEdit here if you need a copy of it.

Using someone else's bootdisk

There's another article at titled Installing 386BSD 1.0 on Qemu. Turns out this has a downloadable disk image in 1.44mb format. There's two images at the top of the article. 5boot.img seems to be corrupt. ddbboot.img is actually a DOS bootdisk that contains the 386BSD kernel in DDB format and uses boot.exe to kick it in to gear.

I booted the latter and ran boot 386BSD.ddb wd1d and nothing... it reads for a bit but just stalls... I wonder if my poor 386 is insufficient with only 2mb of RAM? It has already loaded in to DOS, so there's probably hardly any RAM left and hasn't got a chance to then boot further? The other issue is that wd1d is a hardware device which might only be valid for Qemu?

I'll dig further and see if I can get this working... stay tuned...


Compaq Deskpro 386s/20n: Crystal S23A Audio

Searching through eBay, I was hoping to come across a nice Creative Sound Blaster card. Actually, I found two AWE64s up for grabs... 2 hours left and I was winning the auctions at around $60 a pop. I had mixed feelings as to whether or not I'd actually win them and it turned out my hunch was right: they both went for well over $350 a piece... way out of my price range.

After a little more searching, I came across a merchant in Australia with a large collection of random ISA cards. There were some sound cards, but none of the brands were really well known to me. I saw an Ensoniq or two, but I went budget (more budget than Ensoniq) and opted for the cheapest card in the range. This happened to be a Magic S23A with a Crystal CX4236B-XQ3 chipset. It seems that Crystal offered their chipset to a bunch of manufacturers and that this card could have actually come from Acer, but there is no official branding on the card.

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The card was grotty, but otherwise OK in electrical condition. I gave it a good wipe down with some alcohol swabs and it came up well. The capacitors all seemed OK... but I recorded their values in preparation to replace them. Physically installing the card was straight-forward; the only notable mention was that I shifted the VGA card to the lower of the two ISA slots so that this card (if it was in the lower slot) wouldn't interfere with my CMOS battery hack.


Vogons has a great selection of drivers for this card. Knowing which driver to use is slightly confusing as all chipsets mentioned start with CS instead of CX, but it turns out they're all compatible.

I first tried the v118 driver from this package. All worked perfectly in DOS, but the I couldn't get the Windows portion to work at all. The setup application installs the drivers for you and edits your system.ini, but on boot VSNDSYS.386 throws a nasty error.

I then tried the CX4235 Driver at Vogons, installing it over the top of the driver above. DOS games still worked and Windows did too. But, each time Windows started the mixer dropped all volumes to silent. I had to run the CWDMIX DOS mixer (the latter driver came with no Windows mixer) to re-set the volumes and then things worked. Saving those settings as default did not help as the mixer would set in DOS at startup but then re-set to quiet as windows loaded.

I had no investment in the current Windows installation and so I started again with a fresh install of DOS and Windows. I then installed the CX4235 driver and it all worked perfectly. Still no mixer in windows, and therefore no software volume control, but I had an external one on the Creative speakers anyway.

After a bit of testing, I quickly found out that one channel was distorted/inconsistent/patchy. No amount of external cabling jiggling would fix it. The speakers were also a new acquisition, so it could've been them (they were only $10 at an op-shop), or the card. Trying to determine which was about to get tricky.


Fortunately, I had the case off the computer and I gave the internals a nudge. Turns out that double-jumper setting for Line/Headphones output was the issue. One of the jumpers was not seated correctly and forcing it downwards enabled the second channel correctly. I shut the machine down, removed the jumpers and gave the whole lot a good clean. The card is now performing very well.

I'd never heard of Crystal Semiconductor, but I'm happy with the card after getting the drivers correct!


Compaq Deskpro 386s/20n: Parallel Port CD-ROM Drive

Meet the Micro Solutions Backpack. It's an external CD-ROM Drive that plugs into your PC via the Parallel Port. It comes with its own PCMCIA card which offers a Parallel Port cable dongle. I don't have a PCMCIA port on this 386, so I'm going to attempt to plug it directly into the Parallel Port.

I actually bought it to use with my Amiga 1200, but it turns out that the Amiga doesn't support it out of the box. Fortunately, it is made for Windows... even better, the Windows era that I'm tinkering with!

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It actually has quite a nice slim-line form-factor. Two 25-pin parallel ports on the back will allow you to daisy-chain a printer as well? This hasn't been tested. I fortunately had a Parallel cable lying around (from tinkering with the port back here) and plugged the device in. Everything was connected and ready to test in a matter of seconds.


The Software

Scraping the web for old software isn't fun. So I've provided the download for the driver here. There's a few manuals and larger setup files, but everything I needed was in the DOS folder. I copied these to a floppy and took them over to the Compaq. Since I now had a D: drive, I created a folder named CDROM and dropped the files into it.

SETUP.EXE ran without a hitch from D:\CDROM\. Seems that my efforts to copy it over were pointless though, as it asks for a source disk during install. Selecting D: expected the data to be in the root, so I had to leave the floppy in and copy from there.

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I then crossed my fingers and rebooted. Unfortuantely I was met with a locked up boot. The CDROM driver was trying to load, but freezing. Disabling it allowed my machine to boot. Long-story-short, this driver was conflicting with EMM386! Make sure you load the driver before you start your extended memory manager.

Note that in the folder, there's also a port test application. Use this to find out information about your Parallel port incase things aren't going to plan.


You can find more drivers and information here at minuszerodegrees.

The Result

Back in good old File Manager, we get a new drive (with a new icon!) on the drive bar!


As you can see, the first CD I found was an 'old shit' disk with numerous versions of DOS and WINDOWS. I'll be rebuilding C:\ with this shortly. Time to start from a fresh drive and play games!


Compaq Deskpro 386s/20n: More Disk

So, the old beast is up and running once more. All is well, but I want a little more hard drive space. I've had a 256mb Transcend IDE "Disk on Module" lying around for a long time, so I've decided to install it into this machine.


The IDE connectors on these devices are reversed as they are actually meant to be installed directly into the motherboard. This Compaq does not have a standard IDE connector on the motherboard end, so I'll need a little bit of trickery to get this up and running. I'm going to call this device an SSD from here on; writing Disk-On-Module each time uses my shift key too much.

IDE Pinouts

What I'll try and describe below is where pin 1 is on either end of the cables and how the Transcend module doesn't mate correctly with the 'hard drive' end. For all intents and purposes, we're going to pretend that this Compaq Deskpro actually does have a standard IDE port on the motherboard end. We know it doesn't, but for demonstration purposes, let's stick to the IDE standard.

IDE cables are all female-to-female. Most of the time they have more than one female plug down the cable to allow both a master and a slave to be connected on one channel. The IDE cables in this Compaq are the original 40-pin type. These 40 wires are all connected straight through, down the cable and into the plugs. The drives then determine, via jumper settings, which is to be master and which is to be slave. In this scenario, we can take it for granted that this will occur and that we don't have to modify cables or plugs to allow selection of master/slave automatically.

The best way to explain the pin mapping is sideways. The diagram below shows pin one and two from the motherboard to the HDDs. The important part here is that mirroring occurs and that 1 and 2 seem to 'leapfrog' over each other on the way.


As you can see from above, if we plugged the SSD straight into the IDE cable IDC header then we'd have a mismatched alignment of pins. The top row of pins needs to be swapped to the bottom row. To do this, we either need to put an IDC header on the 'other side' (upside-down?) of the IDE cable, or create a new cable that'll swap the pins around for us.

Due to the staggering of the pins on the IDC header, it doesn't matter which way you orient the plug. The side of the cable is what matters. Then again, this isn't the total truth. If you were hooking up another hard disk, then the rotation definitely matters as the 'notch' must be facing upwards so that pin 1 is to the left (when looking at the 'hole' side.)

Confusing yet? The issue here is that everything is mirrored. Once you then add the rotation, it's a real mind-f##k moment. Either way, for this to work, we'll want to have a plug on the wrong side of the cable. Actually... is that what I really want to do?

You mean, ruin the Compaq IDE Cable?

The IDE cable in this Compaq is proprietary. The motherboard-end is an edge-connector onto the backplane and I can't imagine finding another cable like this, ever. Therefore, we're going to do as little damage as possible to add a slave drive. I could just slap the IDC connector onto the reverse-side of the cable cable, and this would actually minimise any work I had to do, but the issue is that I'd then have to leave a note in the machine to tell the next unsuspecting victim what I'd actually done. Unless you know what you're looking at, you won't have any idea that it's backwards and a normal disk wouldn't work.

Instead, I'll add an IDC connector the correct way, a little way down the cable, as per a standard slave connection. From here I'll then build an adaptor cable that will allow me to female-to-female plug in the SSD. Check the next diagram to understand this.


Note that the 'adaptor cable' seems to be miswired? Pin 1 is pointing to Pin 2!? This is perfectly fine, as that's the cables purpose in life. You couldn't do this with an actual device, but you can with a cable. In the end, if you follow the wires, you'll realise that we now have the pins lined up perfectly. We also have a magical space for the existing HDD!

Building the adaptor cable

After thinking about this for a while, I thought I'd google to see if anyone had done it before. Most people put IDE-CF cards in their ancient laptops, I've even tried to do this before. I then came across an article where Michael B. Brutman installs an SSD into an old IBM L40SX. It was great to see that my concerns of just plugging the 'SSD' into the IDE cable as-is was wrong and that the technique to build a cable was proven.

I went to the shops and bought the required components: ribbon cable and 3 40-pin IDC headers. I already had some rows of header pins available in the cache-o'-crap.


Constructing it was easy enough, just make sure that both your headers are facing up and, just for fun, align the notches the same way. We won't be caring about the notches... but do it anyway!

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Now that we're done, we're going to hack the original Compaq cable slightly... let's put a header on the cable below the current header, allowing for a slave to be connected. Except that we're going to put the master here, using the old header at the end for our new drive. You can see from the shots below that the original cable had enough slack to allow us to fit the header in.

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At this point, prior to plugging in the SSD, test the modification we've just done to the existing IDE cable! After this, the final trick is to just slap it all together. Make sure to set the SSD as the slave! I used the header pin rows, sliding the plastic down mid-way. I then found a power cable Y-Splitter and jammed it all into the case.


Configuring your new disk

Back to the BIOS, you'll need to select a size that is 'just-below' your SSD size. I found a 212mb that I was happy with.


This all worked like a charm. I was then at the usual DOS Prompt. FDISK indicated that I had a new fixed disk and allowed me to to switch to it by using menu option number 5. Doing so showed the old Linux partitions!

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From there it was a quick partition deletion, creation and formatting session. All done in around 5 minutes. The result?


Oh File Manager, how I have missed thee.


Compaq Deskpro 386s/20n

I love old machinery. Apart from the physical presence and the sounds, there's no better reason to tinker with it other than to boot it up and play Railroad Tycoon Deluxe or A-Train. Therefore I purchased a dead Compaq 386 in order to revive it, install a sound card and listen to the beautiful adlib tunes of Railroad Tycoon's intro.

The machine

This poor thing hasn't seen much action for a while. There's dust caked everywhere and the outside of the case is grotty. It's actually a really nice design. Slim form factor with custom floppy drive. Well, not-that-custom... they've just taken the faceplate off and hidden it behind the front case panel. Obviously no room for a CD Drive, but I have a parallel-port model that should work perfectly.


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Opening it up revealed just how custom and proprietary everything was. There was a non-standard power supply with a non-standard connector to the non-standard motherboard. Wait... it's not connected to the motherboard, it's connected to the vertical riser. That's not just for the ISA cards... it also routes power and data to both the HDD and floppy drive.

After a brief visual inspection, I performed the first test... apply power! I already knew it was dead, the seller told me so, so I didn't expect much. Hitting the power switch saw the fan twitch and the floppy drive light illuminate. It then repeated this at 1-second intervals. The power supply was trying to provide current but tripping straight away. No amount of unplugging peripherals would see it start.

Dead power supply

The first point about the power supply was that it wasn't a single removable unit. It's actually built into the case. There's a metal shield, holding the fan, that lifts off. The PCB is then bolted to the main chassis.

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There were some telltale signs already: an odour of ozone and a large patch of fluid residue on the PCB and on the connector to the motherboard. That connector had me worried as well. It's the first time I've seen a direct connection, rather than a bunch of cabling and a plug, between the power supply and the motherboard. Once out, I looked more-closely at the power supply for any further defects.

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Despite the residue, the capacitors actually looked in OK condition. There was no bulging or discolouration. Of course, looks can be deceiving! De-soldering them and looking at their butts showed a different story!


I thought to myself that this was now going to be an easy fix: just replace the damn things. Better point? I actually had replacement caps on hand. Unfortunately, after replacing all caps on the board with equivalent values I still had a dead power supply.

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Replace more components, or buy a spare PSU?

Ok, here's the junction in the road... I mentioned above that the PSU was still dead... but in actual fact I had the HDD spin up for a brief moment! Something triggered the PSU to provide power, but this was short-lived. This could have been because it somehow saw 'load' on the pins, or because it momentarily chose to work. In my excitement, I put the motherboard back in and it all went dead again. Removing the motherboard didn't help; the HDD wouldn't spin up anymore. Still, the fact that the HDD was operational and the noise of that vintage drive spinning up was enough to keep me going.

From this, I could therefore point all fingers at the PSU. There was one on eBay, for over AUD$100, in the UK. That was an expensive gamble for, what could be, a very dead 386. Therefore, my first option should be to replace components in the PSU until it worked again. Looking at the board though, all 'areas of interest' were based around that nondescript Compaq integrated circuit. No amount of googling came up with any results!

The chip reads 114055-002/8072 (C) COMPAQ 1988 RAY H 9006. It's a 24-pin DIP and it's non-existent on the web. No real ability to replace this if I have no idea what it is! The other transformers seem to have dried fluid over them, but this actually seems to be from manufacture? There's a whole lot of power transistors of which look intact. Finding and replacing each one of them would total up to more than the other power supply on eBay is worth. Maybe I should just grab it? If I did then I could at least provide the pinout for this CPU for other users and maybe then repair this unit by working backwards from a functional one.

Further research revealed that the Compaq Deskpro 286N also uses the same PSU. The motherboard is just different, containing the 286 class CPU with all required components. Interesting to know that this 386 machine was built to use existing infrastructure from the previous CPU version. Either way, the googling amped up as I now had a wider scope of information to search for. Unfortunately there was still very little information on this PSU.

Decision to replace with an ATX supply

This was by freak chance. I went on lunch to find more capacitors for the PSU. I knew that these wouldn't help as they were only replacing caps that were actually obviously 100% OK. On the way to the electronics store, I passed a PC store that I've never really been in, as I thought it was all hoity-toity and full of brand new garbage. Turns out they had a random selection of secondhand gear out the back. I saw a tiny PSU (it would fit in the case!) that seemed to have one AT connector on it, labelled P10. Later googling told me that this was not an AT connector, but I got the PSU for AUD$20 when it had AUD$95 marked on it initially! Twas a sign... I purchased the header connectors as well as useless replacement caps.


There was work to be done to rewire the cable, but first we needed to know the pinout.

Determining the pinout

The power supply plugs into the vertical PCB. I don't know what you'd call this component? Maybe a distribution board? Junction board? Daughterboard? It's a vertical riser for the ISA slots, but it also has the plumbing from the disk controller. (Update: it's called a Backplane.) The best part is that the standard drive voltages flow through here. I therefore quickly determined the +12v, GND and +5v. These wires were often duplicated and comprised of the majority of the pins. In short time I had the first two columns of the table below.

Pin Connection ATX Colour Comments
1 -12v Blue 2nd pin, bottom row, MB socket
7th pin, bottom row, ISA socket
I thought this was going to be a challenge... then I traced it to the ISA slot and found the connection.
2 -5v White 5th pin, bottom row, ISA socket
Thank you ISA slot.
3 +5v Red Traced to HDD power connector
4 +5v Red ^^
5 +5v Red ^^
6 +5v Red ^^
7 GND Black These are grounded everywhere
8 GND Black ^^
9 GND Black ^^
10 GND Black ^^
11 GND Black ^^
12 +12v Yellow Traced to HDD power connector
13 Not Connected? I attempted to pull up the plastic on the pin header to see if there were any traces connected. Can't see any!
14 Power Good? Grey 5th pin, bottom row, MB socket
Eep... buried in the motherboard... has to be Power Good?

From here, I had a problem... 2 of the wires fed into the dense motherboard socket. Tracing them further took a bit of work! Here I was assuming that the plug should be similar to a standard AT Power Supply Connector. Unfortunately not. It seems that Compaq (or Miniman) have decided to put a little more logic in the PSU than on the motherboard.

Further tracing saw wires heading to the ISA slots. This is perfect, as it's an industry standard and I could map them. I found -5v and -12v pretty quickly... the final pin went into the motherboard. Must be the Power Good signal.

Rewiring the ATX Power Supply

With the educated guess above on the 'Power Good' signal, I went ahead and wired up the ATX supply.


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With the new cable on... I took baby steps towards testing. Firstly only the backplane with the HDD and floppy attached.

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And then I plugged the motherboard and video card in.


Shittttt.... it woooorrrkkkeedd.... Before I switch to the software realm, I'll make this power supply more permanent.

Making the ATX supply fit

Fortunately this power supply was already tiny. Anything of normal size would not fit in the area provided and it didn't help that the original shielding was slanted. The fan was also mounted on the inside of the shield leaving little room for anything underneath.

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I dismantled the new supply, destroying the leg on a component that was soldered directly onto the back of the power plug. I'd have to transfer these over to the old plug as I couldn't get it out of the case without a lot of extra work. Fortunately, the old power supply had the same component, so I stole one from there.

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I soldered up the old plug as per the new plug's wiring. I then wired up the existing power switch. The old AT power switches had the entire 240v fed through them, and so are quite solid. I cut the plug off and used one pole to switch the green soft power from the ATX to ground. Worked perfectly!

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I desoldered all the cables that I wouldn't need from the PSU. This was quite easy as they're fed in there in clusters! Mounting the fan wasn't fun... but it fit OK up the back on one of the screws that held the shield on. The shield then happily sat on top... a few millimetres higher than it usually would be.

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Quick update: the fan mount was terrible. So I went and purchased a smaller 60mm fan and cable-tied it to the power supply PCB. It actually holds the PCB tighter and in place.

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I previously stenciled out where I'd mount the fan, but now there's no need. Either way, check out the aftermath... here's the debris from the entire operation:


Motherboard Capacitors

Except for the self-test, I held myself back from booting the machine any further. I'd noticed that the rectangular capacitors on the motherboard were corroding and loose. Well, not all of them... 7 to start with, and after a plea for help on the electro-tech-online forums, it turns out I had the relevant 10uf 16v electrolytics in my arsenal.

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Here's a good forum thread at Vogons where people are sharing similar experiences.

With these replaced, I attempted to boot the machine.

CMOS/BIOS issues

Of course, the hardware was never going to be the only problem. On the photo above, you can see the BIOS errors reported on first boot. The configuration data is held by a battery which as long-since expired. Back in the 386 days it wasn't a simple coin-cell either... but I'll talk about that later. Regardless of the battery state, I should have still been able to configure the machine.

Unfortunately, it seems that there is actual no BIOS configuration utility to 'enter' and so Compaq provided disks that loaded into diagnostic and configuration programs. Fortunately, other people on the net have also had to search for them and there were enough results on google. Download the self-extracting archive here. To use this, you'll need a double-density floppy disk. Turns out you'll also need an old machine! The EXE wont run on Windows 10. Virtual Box just threw errors with my real floppy drive and Windows 98 and so I built a brand new Windows 98SE install on VMWare Desktop. That burnt the floppy disk... but the disk then didn't work... it complained that it was the wrong version?


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The screens above are as follows:

  1. SETUP.EXE telling me I have the wrong machine.
  2. TEST.COM telling me I have the wrong machine and to find a newer version of the software?
  3. TEST.COM starting... nice logo!
  4. TEST.COM initial diagnostics list
  5. TEST.COM further machine detail

I tried a few other boot disks... All gathered from AllBootDisks. Starting the machine with DOS 5.0 and then running setup gave me: Packed file is corrupt. This is utter poop, as the same SETUP runs fine when booted by itself.

I then tried a DOS 3.3 bootdisk and it gave me the same errors as above: wrong machine, etc... So it turns out the DOS version determines how well the SETUP program runs. Maybe all these disks are crap because they were burnt via a virtual PC?

There's an entire list of the softpaqs available here. Searching gave me other possibilities, such as Compaq System Configuration Utility v2.58 Rev A SP19624 (actually, that's in Japanese), SP19619 (English), etc... But they're not matching my model. Actually, that index is for much more recent machines. I'd need something from this folder, but the index is incomplete.

But wait, thanks to the wayback machine, we have Compaq's support file listing from 1996. It's all close-but-no-cigar... there's a few interesting 'Rompaqs' in there. They seem to be the flashable ROM BIOS? Maybe there's a version specifically for the 386s/20n.

Hold the phone... the PDF here for the 386N shows my machine in the picture. The PDF here for the 386s/20n shows the 386/20. Were Compaq just lazy and pasted the wrong image? Further digging shows this awesome magazine advertisement from InfoWorld, 1991 (scroll up a little) where it shows my machine with the correct label... lucky... I didn't want a frankenstein.

Meanwhile.. the article here on the 386N indicates that the 'ROM Resident' setup utility (standard for machines of the day?) can be disabled via a dip switch. Well, I know of the switch, but I didn't know how to get into the BIOS. Someone here mentions F10 (find link), but then that is quickly dismissed as Compaq's needed diag disks. Maybe mine doesn't?

Well .. that couldn't be funnier. Indeed my machine just needs the correct keypress at the correct time.

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See that shitty little block in the top-right corner? As soon as you see that, hit F10.


Man, we're in... time to configure disks. Wait. It isn't... we won't be saving anything until we fix the CMOS battery.

CMOS Battery

The motherboard has a DS1287 Dallas Chip for the clock/oscillator and battery backup. This unit is sealed. To get to the battery you literally have to hack it apart.


Fortunately, people have already done this. I've just bought the components to do this hack myself... so, let's spin up the power tools!

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I half killed it. Be REALLY careful when grinding away at it. Either way, my configuration now saves! I even fluked it by getting a battery that has "Lithium Battery" on it in Katakana!

Disk Drives

So, we're booting and we can save CMOS configuration. The clock can't handle the year 2016, so let's pretend it's the year 1991. Due to this machine's vintage, the hard disk configuration in the BIOS is limited. Back then, there was a set table of known disk configurations. Each configuration specified the number of heads, cylinders and sectors which, when calculated together, provided the size of the disk. This machine was meant to come with a 120mb drive... this is option '50' in the BIOS, so I set that.

Reboot and I'm presented with 1782 - Disk Controller Failure. That's a really scary message... I would've preferred something worded with 'drive' rather than controller! What disk do we have in this machine anyway?


What on earth is a PlusImpulse? It looks like a Quantum... oh.. it is... tiny writing under the main brand name. Here's the specifications of the drive. No mention of the matching BIOS HDD table 'number'. Turns out that there isn't one. I found out the hard way by scrolling through the entire 60-odd options.

Quickly checked if the disk worked in my main PC via a USB-IDE adapter. Nothing! Dead drive! Turns out I have a 500GB (yes, gigabyte) IDE drive hanging around. So I tested that on the USB-IDE first and it worked. I then plugged it in to the Compaq and restarted. Same controller error! Quick inspection of the drive: it's in slave mode! Switched to master and there's no more controller error. YES!


That photo above still makes me chuckle. Who would've thought you'd ever see a 500GB drive in a 386? I slapped in a random Compaq FASTART DOS 3.1 boot disk and let it attempt to partition the drive. It really had no chance and kept failing miserably. I really didn't know what to expect when something this large was plugged in.

I tried another 200gb IDE drive which I had lying around. Configured as master, the BIOS then started throwing 1790 - Disk 0 Error. Putting the 500gb back presented the same error? Uh oh. Am I destroying the bus by putting these huge drives on that were never meant to be in 386s? I slapped the original 52mb drive back in and still had the error. Damn.

In the BIOS, to get rid of this error, I was about to set no HDD. Instead, for some reason, I chose a size that was just slightly smaller than the 52mb. On reboot, no error! I still had the DOS 6.22 boot disk in there and, as that I wasn't paying attention, it booted up. There was a different screen up... indicating that installing would overwrite the pre-existing system? What's going on here. I exited and checked out FDISK.


Hah. Wut? It has somehow found a partition. This disk didn't work on the IDE-USB cable... but now it's working here? Have I just, by complete chance, chosen the 'correct' BIOS setting that the previous owner used when setting up this drive? Actually, can you use any disk configuration as long as it is within the bounds of the disks parameters?

Either way, I let it reboot... but it still came up with non-system disk? It definitely tried to access the HD though! I rebooted into the MS-DOS floppy and then ran a benign SYS C:. I could see that all the other files were there, so it may have just needed the minor DOS boot files. Upon reboot... we got to a bloody C:\ prompt!

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AUTOEXEC.BAT pointed to BASEPAGE which no longer existed, hence the errors. There's also a PRINCE folder... no idea. The obvious thing to test was Windows, which booted fine... Paint Brush worked a treat! IT'S ALIVE!... That's enough for tonight... I have more plans for it (hints in the next picture), but this article has gone on long enough!


This has been a blast.