Working through my “to fix” pile, I came across a Sinclair ZX Spectrum 48K+ with an unusual sticker underneath the motherboard and a disturbing lack of many of the passive components. The reason turned out to be the ULA: not the usual Ferranti chip, but an AMI SAGA-1A made in Austria. Nobody I asked had ever seen one in real life, and it runs remarkably cool.
The machine had been sitting in my pile, about twelve Spectrums deep, for around seven years. I only got to it because a flood had damaged my kitchen and I needed to fix and sell a few things.
The sticker and the SAGA-1A ULA
Removing the board revealed the sticker in all its glory.
The ULA bears these markings:
AMI 8444CCI SAGA-1A SRL-VDG-P AUSTRIA
I mentioned it in the Spectrum 4Ever Facebook group, which I help admin and which had around 2,000 members at the time. It generated a fair bit of interest, but no one had seen one of these ULAs in the wild. They are mentioned in later revisions of the service manual, and the assumption in the group is that AMI ULAs were planned but never reached the market, possibly because a Ferranti price cut pushed AMI out of the deal. My guess is that this machine was a pre-production test batch sent to a controlled customer, with the sticker there so it would be returned rather than taken to a local repair shop, where someone would wonder where half the passives had gone.
Does it work?
Yes. The machine passed its pre-power checks. The keyboard membrane later gave up the ghost, so I replaced it (you can see the blue tails in the video), but that is the only work I have done. It is not composite modded, and it loads great from tape. Every title I had to hand loaded fine.
People asked about the colour reproduction and picture quality compared with other Spectrums, so I set the camera’s white balance against a white paper and white border and let a game load in full: Inspector Hector in the Interchange, which I bought back in the day for £3.99 and had never actually loaded. There is some slight vertical patterning in the dark areas, more pronounced on camera than on the screen. I wondered whether the ULA was responsible, since it generates the video signal, but when I checked a standard Ferranti ULA Spectrum the same striations were there too. So I was probably being oversensitive.
How hot does the AMI ULA get?
The thing that really stood out is that this ULA runs super cool. When I first tested it, after ten minutes of Knight Lore there was barely any heat coming from it. For the video I left Road Runner running for about an hour and a half, then used a cheap temperature probe. It is not calibrated to real temperatures, but it is consistent with itself, so the comparison is fair.
- AMI machine, room ambient: about 24°C (the studio lights are warm)
- AMI machine, regulator heatsink: about 35 to 38°C
- AMI machine, dead centre of the SAGA ULA: about 29 to 30°C
- AMI machine, CPU: up to about 39°C
- Ferranti machine after only about 12 minutes of Road Runner, heatsink: 46 to 47°C
- Ferranti machine, ULA: climbing past 40°C to about 43°C and still rising
So even with a fraction of the run time, the standard Ferranti ULA was putting out noticeably more heat. You are really meant to use thermal compound for this kind of test, so treat the numbers as relative, but the difference is clear.
Close-up pictures of the board
People with far greater knowledge than me asked to see close-ups of the chips and components, so here they are (click for full size, and apologies for the quality).
Why I sold it, and where it went
I really did not want to sell this, but I needed the money to repair the flooded kitchen: the hoarder in me wanted to keep it, but the husband and father in me needed to fix the ceiling. I hoped it would go to someone who could unlock its mysteries rather than just load games on it. It was sold at auction to Ian Gledhill at Mutant Caterpillar.
Any observations? Have you seen one like this? Let me know!
Related
If your membrane has also given up, here is changing a Spectrum+ membrane, and for better picture quality try the Spectrum 48K composite video mod.