Acorn Archimedes A3000 Repair

A few years ago I bought an Acorn Archimedes 3000. It had the power plug cut off, but was a reasonable price even if not working. Knowing that these machines often suffered from bad battery corrosion, I opened it up right away. I didn’t actually ever take a picture, but the battery damage was significant. It was so bad it put me off even thinking about repairing it. All I did was remove the battery, and neutralise the corrosion to stop it being even more destructive. The motherboard looked better after that, but you could see there was significant track damage.

Fast forward a number of years, and I was inspired to see a forum post where a repair was done to an A3000 with fairly bad corrosion damage. This encouraged me to pull my A3000 out and have a go.

The picture above is deceiving. This is after I had cleaned up corrosion with vinegar, clipped the battery out, and removed the ROM chips. See how the corrosion has worked its way all the way up into the keyboard ribbon cable connectors.

I have removed most components from the affected areas now. you can see underneath the components the bright green remainder of the bad corrosion.

Battery corrosion is very destructive! Some of the 0 ohm resistor jumpers fell apart while removing them.

I gave the board a bit more of a clean with vinegar and alcohol. It is better now, photo still looks rough.

Many tracks are in a bad way.

Underneath the battery area wasn’t too bad, although the ground track took some damage. The residue you can see is mostly from flux. Can be hard to remove components once solder joints are corroded.

Some stubborn components when desoldering, but no damage done to board in removal.

After a bit more of a clean, to prevent further damage to tracks I sprayed the area with lacquer. I made sure to contain the spray to just the affected area.

It’s a good idea to protect damaged tracks with lacquer.

Now the fun begins. In the affected area I checked every single trace. Luckily there are good schematics available, which make it easy to trace all connections. The schematics can be downloaded from http://chrisacorns.computinghistory.org … awings.zip . Credit to the owner of the site for a fantastic resource. I have added a copy here as well available from the links below. I methodically and carefully checked all components which took a while, documenting everything as I went through. All up there were over 30 broken traces!

Now that I had documented all the broken races, it was time to replace components on the board. Apart from the ROMS themselves, all other chips, sockets and components from this area were removed and replaced. The exception was any SMD components.

The ribbon cable connector (SK6 & SK7) is a bit harder to find. It is a FFC & FPC Connector made by TE Connectivity part number 7-520355-0 available from Mouser. All the other components are easily available from eBay or electronic component retailers cheaply.

Have started adding new sockets , with a couple of traces on top.

Most traces were fixed under the board, as you can see in the following photo.

Many many trace fixes.

After fixing everything up, time to test it out. To start with I tried a composite connection, which only outputs black and white. Because I had replaced the CMOS battery, the first time you start up it will look like the picture won’t sync. To resolve this you need to hold down the Del key while starting up to reset the CMOS memory.

Success! Greeted by a black and white desktop.

Unfortunately I did not yet have a mouse solution, so next steps where to build an RGB SCART cable. I had a decent SCART cable in my box of spares, so I cut one end off and soldered pins through to a 9 pin connector. The pin out for the A3000 is as follows:

There is also a 3.5mm stereo jack on the rear of the A3000, so I broke a stereo cable out from the SCART hood so I could use external speakers.

The completed RGB cable with stereo connector. I had not yet put the backshell on the 9 pin connector.

A handy mod to do at is to bypass the low pass filter, providing much better audio output. This is a simple mod, with more details here https://stardot.org.uk/forums/viewtopic.php?t=13630

For this model the steps are:

– Disconnect the +ve leg of electrolytic capacitors C65 and C70
– Solder a wire from Pin1 of LM324 IC39, to +ve leg of C65
– Solder a wire from Pin8 of LM324 IC39, to +ve leg of C70

The audio mod on this model is very simple.

When I tried the RGB cable out, the colours were a bit off. I thoroughly checked my wiring, and everything was definitely ok. It was then time to go and look at the video circuit. I noticed that underneath a row of diodes that form part of the video output there was more visible corrosion. Look directly under RGB SK14 at the row of diodes.

More corrosion, affecting the video output!

After removing all the diodes, I tested traces that ran through the area and found a couple that were broken.

Corrosion can cause many issues

After adding a couple of traces under the board, and replacing the old diodes with new, the colour output was fixed.

It is often much easier to add traces underneath the board.

Now time to test the keyboard. A number of keys didn’t work. Looking at the membrane ribbon connector, you could see corrosion had made its way inside inside there too.

Corrosion worked its way up under the plastic of the connector.

To verify which connections were related to the non working keys, I removed the membrane and traced the connections. I have provided a couple of photos of both sides of the membrane in case it helps anybody.

After identifying the problematic connections, I scraped away the existing conductive material. In the corroded area it crumbled easily.

Need to expose some good conductive material to make a new connection with conductive paint.

It is a good idea to mask the sides where the new trace needs to go. Conductive paint can be messy when doing detailed work. Having a guide will allow a much neater result.

After applying conductive paint with a small brush, now we have a keyboard connector where all the traces work. Did a test, and all keys work now too!

Next up I need a mouse solution as I don’t have an acorn 3 button mouse. The good news is Amiga mice can work, they just need an adapter for the connector, the only disadvantage is there are only 2 buttons rather than 3.

When building an Amiga to Acorn mouse adapter, simply connect matching pins between the 2 cable ends.

I found an old 9 pin cable with the right plug for the Acorn socket. Simply solder a 9 pin male socket on the other side and connect the matching connections together. One thing to note the mouse socket on the A3000 is in a bad spot underneath, and there is not much room to plug the cable end into the socket. I had to remove the casing from the socket connector on the end of the cable I used, otherwise it wouldn’t fit through the case hole.

After carefully removing the case and resoldering the 9 pin connector pins, placed some heat shrink around the end to help keep together.

The A3000 mouse port is in an awkward located, so the 9 pin mini din may need the outer casing removed.

Thankfully the mouse fully worked. A lot of traces around the mouse socket were broken, so that was a relief.

The floppy drive that came withe this Archimedes doesn’t work properly. When inserting disks, they don’t really click into place. It feels like something in the mechanism isn’t working fully. Rather than trying to fix this, I have gone for a Gotek USB floppy emulator solution. I have opted to use the HXC firmware which costs 12 euro to purchase. However I understand that the FlashFloppy firware will also work on the A3000 if you want a free option.

To use a Gotek you will need a longer floppy drive ribbon cable, and to extend the floppy drive power cable to reach.

As far as I know there isn’t a floppy image manager program available for the A3000.

The HXC firmware has an OSD option where it will overlay the screen using one of the RGB outputs to display the selected file name and list of files on the USB stick. This requires a couple of wires to be soldered to the goteck for sync and video signal, recommend using the green signal. it is best to use probe hooks to clip onto a leg or IC to pick up the signal rather than soldering directly to the computer motherboard.

Probes connected: Check

I chose to pull the green signal from D14, just behind the RGB connector. I pulled the C sync from L24 pin 1 or 2. There is a jumper over pin 1 & 2 of LK 24. I removed the jumper, hooked onto the base of one of the pins then placed the jumper back on.

Goteks are a great low cost modern replacement for floppy drives

When pressing one of the Gotek buttons the screen overlay comes on, allowing you to see what files you are cycling through. When you stop pressing the buttons, the image goes away after a few seconds.

The OSD display isn’t perfect but it is practical.

Good thing about the Gotek and the A3000 is that it fits in perfectly, and even the screw holes line up.

The Gotek is a neat fit in an A3000.

Well have now finished most things I want to do with this Archimedes project. Only other thing I want to do is make a joystick adapter, although this will require a bit more research and planning. It’s not so simple!

As I have never used an A3000, I am very impressed with this machine. My primary interest is games, and from what I have seen so far this would have been capable of some killer arcade conversions. Its a shame it was only home to an impressive but limited number of games. For now time to enjoy this great conversion of Pacmania!


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