From plus, to plusplus (part 1)

Back in the late 1980s, Commodore needed to refresh their best-selling Amiga 500, to give it just a couple more years whilst they developed new models. There was no need to spend big money here, the basic machine was solid; but games were getting more polished, and especially in the UK more and more people were using this home machine for productivity. All it really needed was a bit more memory, and until now A500 owners would slot in something like the A501 memory upgrade – so the decision was taken to make the A500+, doubling both the standard RAM to 1MB just like fitting a memory upgrade except now the trapdoor remained empty, and the upgrade potential via that slot also doubled to 2MB. Great! They also chose to bring the realtime clock over from the A501. That was…. not so great.

The Amiga 500+

Admittedly that decision was fine at first. The clock was a boon for anyone working with files, from word processing to images to game development. It allowed Workbench to understand the date and time, so it could tell you which files were newest and when they’d been worked on. But that is powered by a battery to keep time ticking when the power is off, and in a shocking lack of foresight those 1980s engineers didn’t expect so many machines to be in use in 2020 and rechargeable batteries don’t generally last 30 years. Instead, they leak their corrosive guts all over the vulnerable circuit boards, component legs and tracks simply rotting away.

Varta, Destroyer of Worlds.
How many Amigas ended up in a muddy field with a £2 sticker on them…. or worse?

Many of these machines will have one day refused to work, especially after a spell in the loft, and been deemed as junk. Not too long ago the A500 family reached the bottom of its value curve – from a £299 initial retail price, they took a massive hit in the mid 90s when low price PCs were on the rise from high street retailers like Time and ironically, Escom. They were increasingly seen as toys, redundant or just something to take to the next car boot sale, like C64s were treated a few years prior. Somewhere deep in every landfill site, an A500+ sits with rotting food waste smeared into the keyboard, many miles away from where it last enjoyed a game of Monkey Island or played a few music modules.

But step forward Rob Taylor, aka “Peepo”, who decided to do something about this terrible crime against computers. The task was immense, many A500+ machines have substantial damage which takes hours by a skilled engineer to painstakingly repair one track at a time. The battery corrosion rots through the thin metal tracks that take signals from one chip to another, and in the case of the A500+ the first circuits it gets to control memory access. With these signals stopped in their tracks, the machine is rendered instantly useless typically with a green screen error. Rob’s plan was to simply replace the entire mainboard with a reverse-engineered, freshly made example. Typically the custom chips that give the Amiga its graphics, sound and – well, personality – are well protected and with the exception of poor Gary who is right next to the battery, will have survived the corrosive onslaught so on paper it’s a simple task. Make a new board, swap all the custom chips over, fit a whole load of new components where they’re available, and enjoy a brand new, 30 year old computer.

It’s perhaps a bit flippant to make it sound such an easy task, but Rob made it look easy – and in fact is also responsible for other mainboard remakes such as the Commodore 64. And he isn’t the only one to be working on tasks like this, with John “Chucky” Hertell creating the ReAmiga A1200 and 3000 in a similar way, Floppie209 created the Amiga 2000 remake, and Paul Rezendes remade the A4000. The A2000 and A3000 also suffer similar battery damage, whilst the newer A1200 and A4000 models instead have poor quality capacitors that leak and damage tracks.

The ReAmiga 1200 formed part of the inspiration for the A500++

What happened next was a series of beta versions, testing, modifications and discussions in a small discord group chat. The name A500++ was born out of the thought process that Commodore followed – a couple of tweaks makes a Plus model – and whilst this is a faithful reproduction of the original there’s still space for a couple of nice touches. A floppy drive switch is incorporated so an external drive can become DF0, and a few adjustments were made to allow a new version of a power component to be used as the originals are hard to find. Therefore a couple more tweaks, gets another Plus!

The first red boards needed a few adjustments, so v1.6 followed in beautiful yellow which is where I became aware of the project and offered to test build one. A faulty A500+ was obtained from a local seller for the custom chips, keyboard, drive and casing – and luckily, with this being quite a quiet project to begin with, the prices were still rock bottom for a “dead” machine and it set me back all of £25. A vacuum pump desoldering gun was also obtained as I predicted a lot of time spent harvesting parts, along with consumables, and a space was cleared awaiting delivery of my blank board.

And that’s where we’ll leave it for now. Tune in next time to see how I got on building it. If you like the sound of it already, A500++ boards are available from Rob’s Tindie store.

2 thoughts on “From plus, to plusplus (part 1)

  1. It sounds great! Can you explain what the problem is producing new copies of the early Amiga custom chips Paula, Agnus, Denise, or even the later Paula, Alice, and Lisa using modern technology to produce them? As these chips were originally produced in the time period 1985-1997 (including Escom Amigas) isn’t it possible for other people to produce them now? If not, then why not?

    1. You can make “simulations” of them using modern FPGA or CPLD technology, where you program a chip to behave to inputs and outputs in the same way as the original would. This exists for Gary and the CIAs, and people have demonstrated Paula and Agnus in the same way. The problem with making identical replicas is the factories that used the processes that made them just don’t exist, everything is geared up to make new ICs at lower voltages and smaller sizes so you’d have to spend millions setting up a production line.

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