ZX Spectrum Further Technical Details

 

Board Revisions

  • There are at least 7 revisions (issues) of ZX Spectrum circuit board.
  • Click here for technical schematic diagrams of the ZX Spectrum circuitry.

 

Hover your mouse over the circuit boards for a description of the components

ZX Spectrum PCB

Note: The above PCB is an Issue 3 board

Component details reproduced with friendly permission from Sothius' Home, www.sothius.com

 

ZX Spectrum 128

Spectrum 128 board

 

ZX Spectrum +2 (Issue 1)

Spectrum +2 Issue 1 board

 

ZX Spectrum +2 (Issue 3)

Spectrum +2 Issue 3 board

 

ZX Spectrum +2 Cassette Recorder and Control Circuit

Spectrum +2 Cassette recorder with circuit Spectrum +2 Cassette circuit board (zoomed)

 

   
RF modulator for TV out MIC (Microphone input) socket EAR (earphone output) socket ULA (Uncomitted Logic Array) - used for I/O functions such as the cassette interface. This is similar to the ZX81's SCL, but also responsible for generating graphics. The first 16K RAM bank (8 x 16Kx1 DRAMs) The expansion RAM bank (8 x 64Kx1 DRAMs). These DRAM chips are socketed, and on the 16K Spectrum, these sockets are not filled. Loudspeaker Zilog Z80A Microprocessor (CPU) - a descendent of the Intel 8080 16K BASIC ROM (contains the operating system, BASIC interpreter and character generator) Heat spreader for the voltage regulator DC power in (9V @ 1.2A) Voltage regulator Expansion port (under metal heat spreader) 5 Logic chips that act as RAM address decoders and multiplexers (2 are obscured under the metal plate). These 5 chips were replaced on Issue 5 and above boards with a single ULA to reduce production costs. Keyboard ribbon cable connector 64K RAM memory chips (2 x 4164) External numeric keypad port RS232 (Serial) port Joystick Port 2 Joystick Port 1 Keyboard connectorRF modulator for TV out Zilog Z80A Microprocessor (CPU) - a descendent of the Intel 8080 Reset button General Instruments (GI) AY-3-8912A sound chip 16K BASIC ROM (contains the operating system, BASIC interpreter and character generator) RGB video out connector Parallel port edge connector Power in (9V DC) Expansion Slot edge connector Cassette recorder connector Keyboard connector Custom chip 64K RAM memory chips (2 x 4164) Custom chip used for I/O and memory management External numeric keypad port Joystick Port 2 Expansion Slot edge connector RGB video out connectorRF modulator for TV out (not present in some countries) Zilog Z80A Microprocessor (CPU) - a descendent of the Intel 8080 Reset button General Instruments (GI) AY-3-8912A sound chip BASIC ROM (contains the operating system, 48K and 128K BASIC interpreters) Sound output jack Joystick Port 1 RS232 (Serial) port Heatsink (5V regulator) Custom chip under heatsink (used for video and character generation) Keyboard connector Keyboard connector Custom chip (used for I/O) 128K RAM chips (16 x 4164) Cassette recorder connector 5V power connector RF modulator for TV out Zilog Z80A Microprocessor (CPU) - a descendent of the Intel 8080 ULA (Uncomitted Logic Array) - used for I/O functions such as the cassette interface. This is similar to the ZX81's SCL, but also responsible for generating graphics. Reset switch 128K RAM bank 16K BASIC ROM (contains the operating system, BASIC interpreter and character generator) Heatsink Keyboard ribbon cable connector General Instruments (GI) AY-3-8912A sound chip Another ULA (Uncomitted Logic Array) chip Expansion Slot edge connector RGB video out connector