Tag Archives: Acorn

Making the Old work with the New

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Yesterday, I took my Acorn A305 – a 25 year old computer – to another Paul who has developed a rather cunning way of getting these old machines to display correctly on a modern LCD monitor.

After some soldering (a skill I have not developed) and some detective work with some jumpers (used to various control signals to/from the video circuitry), the machine’s upgrade was completed, and we got a display on an LCD screen. I say “we” – Paul was the one doing most, if not all, of the work here.

The really clever bit is that the modification is software controlled, so no need for manual switching. The software knows what signal to send to the monitor and flips the added hardware as required. So it’s invisible to the user. Clever stuff indeed.

For more on this, visit Paul’s website: http://www.retro-kit.co.uk/VIDC-Enhancer/

These are now available to buy: http://www.retro-kit.co.uk/site_news.cfm#NewsID38

More Lego “8-Brick” computers!

I had a lot of interest in the Lego ZX81, you may be interested to know that I’ve also been working on others as well in Lego’s Digital Designer software. Some are closer to completion than others. Here’s what I currently have on file. Will they make it to real Lego models? Hopefully, yes. Sadly Lego closed down the service that gave me a proper kit in January, so I’d have to order future models brick by brick. No exciting box or instructions!

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Sinclair’s follow up to the ZX81 – the ZX Spectrum. This is almost done – I’m in the process of seeing if I can reduce the brick count on this model a bit. The red 1×4 plates sticking out of the base of the model is there to help the software “lock” the lid on (so I’ll know if it all fits together). Eventually, there will be flat plates there, which will allow the lid of the machine to rest on the top without being fixed. Much like the ZX81 model, the Spectrum has a PCB inside. I may include a Lego Rock Dickinson minifig with this one if I can find a picture of him from the time!

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Cambridge Computers Z88. This was Sinclair’s computer post Amstrad sale (Sinclair sold the name as well as properties to Amstrad). This is a little less developed as a model. I’ve got the screen, keyboard and base plotted out. I have to fix the screen to the base, put in some PCB stuff and check they all fit together. And, yes – those are batteries! The Z88 ran on 4 AAs.

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Acorn Electron. This is moving on, but I have a small problem with the keyboard. Unlike the Sinclair machines, which had their own more unique keyboards (which lend themselves more to being modelled in Lego), the Electron had a full size keyboard. The problem I am having at the moment is that there is no Lego brick that looks like a key. So what I have done is made an impression of them out of existing parts. I am not sure if these will make the grade or not. If you have any thoughts on the keys – do they work for you or not? – then let me know in the comments below. Remember, this is Lego, which is a fairly low resolution thing (something I like because 8 bit computers had pretty low resolution graphics). I am looking for an approximation – something which will work within the confines of the medium.

If I can get the keys right for this model, then this opens the door for other machines with more traditional keyboards – most notably the BBC Model B which will be a major undertaking, and will (for me anyway) be the flagship model. I plan on that one being a representation of my own BBC Micro, complete with internal expansions on the motherboard. It’s a big thing, and costly, and I want to get it right. Minifigs of Chris Curry and Hermann “Your Prussian Friend” Hauser may well join the BBC Micro model.

There is an Atari console in the loft. That will get the treatment eventually too. It has those iconic joysticks, which should be fun to model.

Reviving an Archimedes

The other week, I switched on an old computer – my Acorn Archimedes (http://en.wikipedia.org/wiki/Acorn_Archimedes). It’s a 300 series machine, which makes it 24 years old. It started up, then started again, then again and then went dead. It hadn’t been started for a few years and knowing that the BBC Micro has problems with the power supply unit when it’s been left for a long time (they tend to blow capacitors), I suspected that this was the case here.

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So, myself and a friend, Chris, set to to find out what was wrong. I’m not an electronics expert, and I certainly have no skills with a soldering iron, but Chris can do all of this, and a lot more, so between us we took the machine apart and started testing. As we went, I took pictures – mostly for reference – so we knew where the bits, wires, etc. had to go when reassembling. The PSU was the main suspect, but initial tests showed that it was supplying power – all the right voltages came out from the right connectors. It seemed that there was a problem somewhere else – very likely on the main circuit board.

In fact, it seemed that the machine booted up when the 12v supply was not connected. All that could be gleaned from the circuit diagram that I’d downloaded from http://www.drobe.co.uk was that this powered the fan, and sent some juice to the backplane. On the stripped down circuit board, it seemed that there was all the 12v supply did. The fan connector is unoccupied on a base A300 series machine, but on mine it’s used to blow air over the hard drive I’d installed, so it’s necessary.

So, while Chris followed tracks, I followed Google. I found this link: http://forums.nekochan.net/viewtopic.php?f=8&t=16721049 where the original poster lists some symptoms about an A300 series: &ldquoSadly it didn’t start – the PSU buzzed at switch on – this was traced to a shorted tant. cap in the 12V rail.” That was the clue. This machine was doing exactly the same thing.

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Chris said that the capacitor in question was regulating voltage on the circuit, possibly to cancel noise or smooth out the power supply. To me it sounded a bit like an angry appendix. Anyway, what it now appeared to be doing was causing a short circuit, and this in turn was making the PSU go into some kind of protection mode. So Chris removed the capacitor, and cleared the area from shorts.

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We then started the process of reassembling the machine, slowly and testing start up at various points along the rebuild. It started up every time – the machine, it appears, has been saved.

The capacitor is this small, yellow blob-like thing. It looks OK from the outside, but it’s probably mashed inside. This is the culprit.

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A set of photos of the internals of the machine can be found here.

When I got the machine home, I tried booting it again, and it started up first time, and it seems that removing the capacitor was all that was needed to restore functionality.

For those who are interested, Chris highlighted the errant component on the circuit diagram in red:

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Reviving a RISC PC

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This is an Acorn RISC PC. It’s been sitting dormant in storage, somewhere which up until this week I thought was OK. Apparently not – because on the circuit board is a NiCAD battery which trickle charges when the machine is power up. This battery maintains some RAM, as well as the clock, so user settings are maintained and, as you would expect, the time is correct when you switch it on.

However, if unused, the battery will start to leak. This is not good because the acid will spill onto the circuit board and ruin it. So I got the machine from storage, and armed with a screwdriver, some wire cutters and a soldering iron, I removed the battery and wired in a holder for a rechargeable AAA battery, which is kept out of place away from any electronics. Should the battery rupture now, it won’t do any damage to the electronics.

Here’s the fix.

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I’m not great at soldering, and this is the first time I have attempted anything like this in a computer. However, it appears that it’s working. The battery held a charge overnight, and it started up with the clock showing the correct time this morning. The recharging part of the circuit had obviously worked as it was new and hadn’t been given much electricity before I installed it. I replaced the battery with one which had been fully charged over night.

The other problem was the hinged front. The picture at the top shows it open. This is because the spring that kept it shut had broken away from the from the lugs that hold it in place, and had made it’s way under the hard drive. A small hole and some wire reconnected the spring to the case and the door, and it opens and shuts with a rather satisfying clunk.

So I’m feeling rather pleased that I’ve fixed this machine, and it’s now in a better condition that it was at the beginning of the week.

Here are some more pictures of the RISC PC’s innards.

Firing up the Electron

I have an Acorn Electron. It’s the second one I’ve owned. The first being a rather temperamental example that I bought in 1984. It kept breaking down, so I managed to get my money back on it. It was spending more time being mended that I was using it for playing Elite hard work and study. To be fair, it did kick off a project for my computer studies at school, but that ended up being completed on a more powerful BBC Model B there.

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This Electron came my way during the last few weeks at University. A lecturer had one in his office, and I just happened to tell him what it was. I was actually quite surprised to see one, especially in this configuration. He said I could keep it. He didn’t want it, and he didn’t know what he could use it for anyway. So, I took it home, and borrowed a power unit which would work with it to test it. It worked.

What this is is an Acorn Electron (the bit with the keyboard), and two extra add ons which bolt onto the back. The Plus 3 is the 3.5″ disk drive, and the Plus 1 which has cartridge slots, as well as a joystick and printer port around the back. The Plus 1 was fairly common, but the PLus 3 was less so. I don’t think I ever saw one outside of the Acorn User shows I used to go to.

It’s been bouncing around the place unused for a long time. The problem with not being able to switch it on was the lack of a power adapter. It’s a bit of an odd specification – 21V AC – nothing I have offers that kind of juice, so I turned to eBay. It was a while, but eventually something turned up. An unknown “Acorn” branded power supply – 21V. The seller didn’t know what it was for, but in the photo was the plug – with the letters “ADFS” in Dymo lettering. To someone who knows Acorn hardware, this means “Advanced Disk FIling System” – and that is just what the Electron Plus 3 has. This was, I surmised, the long lost power supply unit I need to run this machine. I bought it, and it arrived last week.

The Electron started up – but there was a problem. Right near the plug that connects to the machine was a nasty kink in the cable. This was causing power fluctuations, as well as, at times, failing power ups (and odd display artefacts). A trip to a well known electrical store and an adventure with a soldering iron later, I was able to test the machine with a healthier looking power lead.

It wouldn’t start! Yikes! Had I broken it? My thoughts were that there may be a bad connection somewhere between the expansion units, so I unbolted the PLus 3 and Plus 1 units, gave the connectors a wipe, and reassembled the machine. I knew I could not just test the Electron on its own – the voltage would probably cause it to really pop a fuse, or worse. So it had to work with the Plus 3 connected.

Power applied again, and…

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It started. The picture on the modern TV is excellent, and it remained up and running without any further power fluctuation oddities. I was surprised that the modern TV coped so well – bit it has some nice backwardly compatible sockets, and upscaling the picture to that size didn’t seem to be a problem.

Next step – sourcing a Welcome Disk. That has the all necessary formatting and other disk management software which wasn’t put on the ADFS ROM. It seems that Twitter may be answering that particular problem.

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More on this project as things develop.

See more photos of this machine here:

More about Acorn Electrons here: