Acorn System 1 Circuit Diagrams
The Acorn System 1 circuit diagrams are Acorn Computers' drawings of the two Eurocards that make up the Acorn System 1. The hosted PDF has three A4 pages and no text layer. They are the sheets that the Acorn System 1 Technical Manual lists as supplied loose, and their reference numbers match the board numbers in that manual.
The sheets
[edit | edit source]| PDF page | Title | Reference | Notes |
|---|---|---|---|
| 1 | Keyboard, Display & Cassette Interface P.C.B. | 200,001/C | Drawn by CBT; issue 1 dated 26 February 1979, issue 2 dated 11 July 1979. Shows the NSA1198 display, the key matrix, the 7445 digit and scan driver, the CMOS cassette tone logic and the LM358 cassette amplifier. |
| 2 | 6502 Micro Computer P.C.B. Circuit Diagram (left half) | 200,000/C | Issues dated 23 February 1979, 11 July 1979 and 27 March 1980. 8154 (IC2) to the keyboard connector, 6502 (IC1), 2114 RAM (IC3, IC4), address decoding (IC9 to IC12), the 1 MHz crystal oscillator and the reset, IRQ and NMI networks. |
| 3 | 6502 Micro Computer P.C.B. Circuit Diagram (right half) | 200,000/C | Copyright 1980. ROMs IC5 and IC6, EPROM socket IC7, second 8154 (IC8), address select links, the 64-way edge connector, the LM340-T5 regulator (IC13) and the decoupling capacitors. |
Mike Cowlishaw describes the same set as a main board schematic in two halves and a single keyboard sheet, and credits the drawings to Christopher Brian Turner (initials CBT).[1]
What it settles
[edit | edit source]- The CPU card regulator is IC13, an LM340-T5, with C10 (15 µF 16 V) on its input from edge connector pin 31. A note on the sheet says to remove C10 and IC13 before fitting the link that feeds the card from a rack's 5 V supply.
- The keyboard card has no regulator; it takes +5 V from the CPU card on pin 20 of the 20-way connecting strip. Its only electrolytic, C5 (15 µF), is on the bias divider (R6, R7) of the LM358 cassette amplifier. C7 is marked not fitted.
- The positions of the reset, IRQ and NMI switches and their RC networks, and the alternative ribbon header connections for issue 3 boards.
What these drawings do not contain
[edit | edit source]- No parts list or Acorn part numbers; those are in the Acorn System 1 Technical Manual (pp. 25–30).
- No PCB layout; the Technical Manual prints the layouts on p. 24.
- No power supply design beyond the on-card regulator. The Technical Manual gives a home-made supply circuit on p. 13.
Pages that cite this document
[edit | edit source]- Acorn System 1
- Acorn System 1 Maintenance Guide
- Acorn System 1 Troubleshooting Guide
- Acorn System 1 Capacitor Replacement Guide
Download: Acorn System 1 Circuit Diagrams.pdf
References
[edit | edit source]- ↑ Cowlishaw, Mike. "Schematics" and "Timeline and people", The Acorn 6502 Microcomputer Kit (speleotrove.com), 2001–2002, retrieved 2026-10-01.