Posted on May 11, 2005
To maintain the original outward appearance, the new power supply had to sit inside the case and connect up to the old switch on the back of the machine. The original switch and power lead were both part of a self contained supply module that sat on the left hand side of the B. I removed the old supply from the metal casing but unfortunately the new power supply didn't fit nicely into the space. To make it fit I removed the outer black plastic case and replaced the plastic power connector with flying leads. I then soldered a new, shorter output connector to the power supply so that I didn't have a really long piece of cable trailing around inside. To finish off, I soldered a modern day hard drive power connector onto the leads of the auxiliary output supply on the B. This would give me a power connection for an external DVD or floppy.
To mount the hard drive in place I made a little bracket to using a couple of expansion slot blanking plates from an old PC. Two mounting bolts for the hard drive were screwed through the plastic that separates the power supply from the main area. Another was then attached to the little bracket to support the weight. The supporting bracket was mounted so that it would sit between the Ethernet and LPT1 socket outputs on the motherboard. The cables that connect the external sockets to the motherboard were then made and put in place before the hard drive was fastened in.
To get the machine to power up was more difficult than I'd imagined. The original B powered up as soon as you turned on the mains switch at the back. However, the ITX power supply only comes on when the power on pins are connected and disconnected on the motherboard. To overcome this I constructed a little 555 timer circuit that closes and opens a relay just after power is applied. When the relay is connected to the power on pins on the motherboard, it boots up nicely. This small piece of circuitry was mounted on top of the UHF connector box at the back of the case and was powered using the 5v supply from the on board PS2 connector.
The keyboard was then fixed in place and a floppy and CD-ROM used to install Slackware 10 onto the empty hard drive. Of course the project wouldn't be finished without a BBC emulator to run the old games (I used BeebEm).
I have still got quite a list of things I'd like to do to the machine. Initially I have to connect the 2 USB outputs to either the analogue input socket or the cassette port. The cassette port only has 7 pins so I'd have to connect the two grounds together. I'd also like to re-connect the IDE connectors underneath so that I can hook up a parallel printer, floppy disc and perhaps connect a DVD drive to the Tube port. I don't know whether it's possible but it would be good to get the old 5.25" drive connected and modify the emulator software to read in original BBC floppies. Lastly I need to have some sort of connector for using a normal PC keyboard (maybe the user port). The problem with the current one comes when operating in BIOS or when installing Linux for the first time when the BBC key map is not available. When the connector is pushed home it could perhaps disconnect the internal keyboard (via a relay) and connect the external one instead.
Until then I'll just enjoy playing all those old games, Exile, Repton…