Sinclair Spectrum Motherboard Issue 3

Sinclair Spectrum Motherboard Issue 3


Issue 3 Motherboard

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.

Each component link below will provide more information and an image of the component in question.


Components

COMPONENT Qty Description
Z80A CPU 1 Main Zilog CPU
8428 STC 4116 Static RAM 8 16384-bit Dynamic RAM
M3732H 8 32768-bit Dynamic RAM
D23128C ROM 1 Programmable ROM
LOGIC CHIPS
Ferranti ULA 1 Uncommitted Logic Array
SN74LS00 1 Quad 2-Input NAND Gate
SN74LS157 4 Quad 2-Input Multiplexer
SN74LS32 1 Quad 2-Input OR Gate
VIDEO SYSTEM
UM1233 UHF Modulator 1 RF Modulator PAL System
LM1889N Modulator TV Video Modulator
VOLTAGE REGULATOR
7805 Voltage Regulator 1 5 V Regulator by NEC
MISC
3.5 mm Audio Jack Sockets 2 Mono
Speaker 1 Moving coil Speaker
Motherboard Issue 3 PCB 1 Track side of the PCB
Ribbon Cable Socket 2 For the Keyboard