ZX Spectrum Repair and Upgrade

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A kind Freegle user gave me a big collection of vintage home computer equipment a few months ago including 4 48K ZX Spectrums in various states. The photo above shows one of them connected via the aerial RF socket as a test. The random pattern is a typical ssymptom of failed memory ICs. 

The first job was to examine the main boards in each of the 4 computers. 3 were Spectrum+ units in the bigger case with the better keyboard and 1 was the classic Spectrum with the rubber keyboard. Unfortunately the classic's case was in very poor condition, but 2 of the 4 main boards were suitable for restoration along with at least 2 of the Spectrum+ cases.

The 7805 regulator is a linear type and generates a lot of waste heat, hence the big heatsink. These can be easily replaced with a high-efficiency TSR1-2450 swich-mode type so that the heatsink can be done away with.

The next job is to modify the RF modulator to output composite video. This just requires a 100uF electrolytic capacitor and a bit of rewiring.

I modified 2 of the boards and both were generating rubbish, but one board had the lower memory (8 4116 DRAM chips) in sockets, so with a bit of desoldering from the salvage boards and trial and error, I found 8 working chips.


At last, the iconic Sinclair 1982 welcome message.


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