We have previously reported on a project that Askaris is involved with at the National Museum of Computing at Bletchley Park. This weekend saw Askaris’ Technical Director Sean Allison and his brother Ray, spend another weekend down at the museum in Milton Keynes continuing with the restoration of the iconic Scrapbook system built by NPL in the early 1970s.
Ray concentrated on working on the CPU – a DEC PDP 11/70, which was in great need of some TLC. After 2 days and our first smoke incident of the weekend, Ray had the CPU in a stable condition and was able to load simple machine code programs using the front panel which proved the system’s integrity. The system runs from 8 separate power supplies and one power supply decided it had had enough and switched itself off in a cloud of smoke. A replacement was taken from a spares machine and the system was once again in an operational state.
Sean worked on the first of the disk drives – a DEC (CDC) RM03 disks with a 67Mb storage capacity. The drives were in a sorry state with many years of dust and debris covering the internal workings. They had last been used in 1987. With the assistance of Henry (the vacuum cleaner) and a brush, much time was spent dismantling the drive and giving everything a thorough clean. True to form, the first power-on of these disks for around 30 years ended in a cloud of smoke! Working with the original circuit diagrams, the problem was traced to a short circuit capacitor on one of the logic boards. Replacing the capacitor from stock held at the museum, the disk drive successfully powered up. Sean then spent 2 hours thoroughly cleaning the critical components within the drive (carriage rails and head surfaces) and we were ready to spin up.
It was at this point we had our 3rd smoke incident of the weekend as the start capacitor decided it had also had enough of life and started smoking with the unmistakable smell of cat piss! Electronic components can degrade over time – especially over periods as long as 30 years so none of these incidents were unexpected. A replacement capacitor was fitted and we ended up with a fully working drive which was left running for an hour and seems to be working as it should.
The next visit will see the restoration of the 2nd disk drive and we should hopefully be in a position by the end of the year where we can load the original Scrapbook media and start the critical task of data recovery.