Sinclair Spectrum Motherboard Issue 3

Issue 3 Motherboard

The Sinclair Research Company manufactured this Spectrum Issue 3 motherboard in approximately 1983. This motherboard became a classic, as it was the most used out of all the boards. They used a computer to design the printed circuit board layout, and consequently the tracks are uniformly spaced. In addition, the clock oscillator tracks are away from the memory chips to reduce the risk of crosstalk noise.

This board has two groups of memory chips, consisting of eight 4116 integrated circuits (IC) providing 16 KB of memory for a possible 16 KB Spectrum model, and a group of eight M3732H ICs providing 32 KB of RAM, hence making a total of 48 KB. RAM

The Ferranti ULA helps to reduce the chip count; however, it was not enough to eliminate all the logic chips, and there are still four 74LS157 ICs, one 74LS00, and one 74LS32. The NEC D23128C single shot programmable ROM served as the permanent storage space for the operating system and the Sinclair BASIC interpreter. User written programs had to be stored on cassette tape using a standard cassette tape recorder.

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Components