I’ve had a stab already using my limited tool kit by following this guide (http://www.worldofspectrum.org/SpectrumRepairGuide). I’ve got as far as checking the board visually (well, it looks okay) and metering out the power (that checked out fine).
The rest of the guide is all cutting tracks and bending pins and to be honest some of the legends are difficult to read on the hand-drawn diagrams.
As luck would have it I will be getting a digital oscilloscope with a 16 channel logic probe (http://www.picotech.com/mixed-signal-oscilloscope.html) for use at work to diagnose faults with circuit boards and act as a serial protocol analyser. I will probably use this duff Spectrum as a test board to familiarise myself with the scope.
It appears that there are lots of places online where I can purchase ULA’s and Z80’s. I’m slightly surprised about the ULA as the ZX series ULA’s were custom parts made by Ferranti.
Remember, fixing a Spectrum can be fun. I’m planning on blogging my progress. Keep watching this space!