BBC Microcomputer Service Manual
Acorn’s official service / repair manual for the BBC Model A/B (Issues 1-7 of the PCB). Covers electrical-level circuit operation, fault-finding, link options, and upgrade procedures.
Out of scope for most performance/demo work — this is a hardware-repair document, not a software reference. Useful contributions to the wiki are:
- Reset distinction (§3.1): cold start (power-up via “Reset A” signal) vs warm start (BREAK key) — distinguishable by polling System VIA IFR on entry.
- Specific IC numbers on the Model B PCB for cross-reference with the address-translation page (IC32, IC39, IC9).
- DRAM CAS arrangement: Model A = single bank (CAS1 only); Model B = two banks (CAS0 lower 16K, CAS1 upper 16K).
- Link options (§5): factory configurations and selectable options.
- Hardware hints (§7.3): potentially demoscene-relevant electrical tricks.
For chip-level documentation, prefer the per-chip pages (6502, crtc-6845, video-ula, etc.) which have been built from primary manufacturer datasheets.
Bibliographic
- Title: BBC Microcomputer Service Manual
- Publisher: Acorn Computers Ltd.
- Year: 1982 first edition; updated through ~1985 to cover PCB issues 1 through 7.
- PDF source: bitshifters/bbc-documents archive
- Format: 90 pages including schematics and parts lists.
Section index
| § | Title | Pages | Filed into |
|---|---|---|---|
| 1 | Introduction + specs | 5-8 | out of scope (specs) |
| 2 | General Description of Hardware | 9-12 | out of scope (overview) |
| 3 | Detailed Circuit Description | 13-27 | Cross-checks against per-chip pages; Reset-A note filed in break-intercept |
| 4 | Upgrading the PCB | 28-40 | out of scope (repair procedures) |
| 5 | Selection links and circuit changes | 41-50 | out of scope (historical PCB link config, factory-set) |
| 6 | Servicing and Fault-finding | 51-60 | out of scope (also contains the canonical “test ROM” routine for finding dead machines — historical interest only) |
| 7 | Interfacing Survey | 54-60 | §7.3 reviewed — hints are end-user PCB mods (110 baud trick, BREAK-key disable). No demoscene-relevant tricks. |
| 8 | Component location tables | 68-75 | out of scope (parts list) |
| 9 | Appendices (schematics, parts list) | 76-90 | out of scope |
Filed into
- §3 (Detailed Circuit Description) → cross-checked against existing per-chip pages. Added cold-start vs warm-start “Reset A” mechanism note to break-intercept. Confirmed IC numbers for address-translation (IC32 addressable latch, IC39 74LS283 adder).
This wiki is curated by Claude following the LLM-Wiki methodology — a human curates source documents, the LLM compiles structured cross-linked markdown. Content may contain errors, omissions, or stale claims. For authoritative information refer to the original source documents in the bbc-documents GitHub archive.