The Imitation Game: Fact and Fiction

Last weekend saw the release of ‘The Imitation Game’ in which Benedict Cumberbatch and Keira Knightley star as Alan Turing and Joan Clarke, codebreakers that helped change the course of the Second World War. Amongst an ensemble cast, the story of Turing is told in three parts; his school days, Bletchley Park and his final, desperate years in Manchester.

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The ZX81 Mystery Board

Well, my post on the ultimate pimped-out ZX81 drew a lot of attention; mostly centred around the mystery expansion board that was included in the myriad of components of which this behemoth was comprised. A closer picture shows it to be some kind of EPROM from  ‘Orme Electronics’.

2013-10-13 15.04.56

But what does it do? Well, the best clues can be found from the wonderful ZX81 Stuff resource. Sadly, I can’t find any photographs to confirm but it looks to me to be the first item in their Orme list. It can’t be an EPROM programmer as the chip is soldered in and there would be no practical way of removing it if it wasn’t. Without instructions I’m still a bit lost but I’m going with an EPROM programmed with Breakout, Life and a Toolkit of some description.

 

 

Pimp My ZX81

I’ve been systematically going through The National Museum of Computing‘s collection of Sinclair equipment. It’s taken a good few months and finally I’m at the point of going through those items that, at the time, where placed in the WTF? pile. The latest candidate to come under scrutiny I have affectionally called Bluto.

Bluto 1

Pretty, huh? Yes, it’s an extremely pimped-out ZX81. I don’t have a record of the donor and have so far failed to identify the kit used to expand this humble little ‘pooter into the 80s microcomputer equivalent of an Apache gunship. Let’s have a look inside:

Bluto 2a

Wow. So, we have:

  • A keyboard which seems to be of DK’Tronics origin
  • A ZX Printer
  • The PSU
  • The mother of all cooling fans
  • An expansion board for the Z80 bus (although I have no idea how you would make use of it with the cover on)
  • A 16K RAM Pack
  • Some kind of expansion board of whose purpose I have no idea
  • Loadsa wires

Having established that nothing was going to explode upon power-up (being as sure as you can ever be with these things), I plugged it in and fiddled with the power switches. One slight annoyance with testing ZX81s is their complete silence. It’s always going to involve some mucking about to establish whether they are getting power or not (tip: multimeters help). Anyway, I tuned my old CRT tele in and got this:

Bluto 2

Ah.

So, is the ZX81 itself borked or, as is often the case, some other peripheral interfering with things? Having removed the motherboard (which turned out to be a very simple job despite the hundreds of screws holding this thing together), I quickly established it was indeed in a state of borkdom. Luckily, I had a replacement board ready and waiting and so swapped them over.

Bluto 3

After a lot of cleaning, especially of the peripheral connectors, and a little gentle pushing and pulling, Bluto sprang to life once more.

Bluto 4

A real surprise was the ZX Printer, which happily sparked away onto its thermal paper.

Bluto 5

But seriously, who used such a thing? Yes you could drop it off a cliff without consequence but it looks like someone had a serious purpose for it and can’t image using Bluto for anything more than a few minutes. The fan is unbearably loud (although thankfully optional via its own switch) and the key-response time slower than an underachieving sloth. Still, maybe it go on display one day as it’s got a better chance against the regular museum key-bashing than an original membrane keyboard.

The only thing that bugs me is that expansion card. What does it do? Any ideas?