Acorn System 1 Capacitor Replacement Guide
This guide lists the capacitors on the Acorn System 1 (Acorn Microcomputer) and gives the replacement procedure. The values and designators are taken from the Acorn System 1 Technical Manual parts lists for the CPU card (200,000) and the keyboard/cassette card (200,001).[1]
Why (and why not) recap a System 1
[edit | edit source]The System 1 has no mains wiring and no CRT and runs on a low-voltage supply, so capacitor work is low-risk bench work. Each card carries only ceramic decouplers plus a single 15 µF/16 V electrolytic on the +5 V regulator. There is no large reservoir capacitor and no notorious failure pattern; replace the two electrolytics only when a card is already open or shows ripple-related instability.
Capacitor list
[edit | edit source]| Designator | Value | Type |
|---|---|---|
| C1, C2, C5, C6, C7, C8, C9 | 100 nF | Ceramic decoupler |
| C3, C4 | 10 nF | Ceramic |
| C10 | 15 µF / 16 V | Electrolytic (regulator) |
| Designator | Value | Type |
|---|---|---|
| C1 | 100 pF | Ceramic |
| C2, C4 | 1 nF | Ceramic |
| C3 | 10 nF | Ceramic |
| C5 | 15 µF / 16 V | Electrolytic (regulator) |
| C6, C9, C10 | 100 nF | Ceramic decoupler |
| C8 | 22 nF | Ceramic |
| C7 | — | Not fitted |
The Technical Manual notes that the 0.1 µF (100 nF) decouplers may be substituted with 0.047 µF if needed, and that the 15 µF electrolytics are polarised (observe the + marking).[1]
Replacement summary
[edit | edit source]The only recap targets are the two electrolytics:
| Value | Voltage | Type | Where |
|---|---|---|---|
| 15 µF | 16 V (or higher) | Aluminium electrolytic, radial | C10 (CPU card), C5 (keyboard card) |
Use a 105 °C low-ESR part of equal capacitance and equal-or-higher voltage. The ceramic decouplers are stable and are left in place.
Procedure
[edit | edit source]- Power off and separate the two cards.
- Mark the polarity of each 15 µF electrolytic (the silkscreen marks the + end).
- Add fresh solder/flux, remove the old cap, clear the holes with solder wick.
- Fit the new cap, matching polarity; solder and trim.
- Verify +5 V at the regulator and confirm the monitor prompt and keypad on power-up.
Related pages
[edit | edit source]- Acorn System 1
- Acorn System 1 Maintenance Guide
- Acorn System 1 Troubleshooting Guide
- Acorn System 2 Capacitor Replacement Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.0 1.1 Acorn System 1 Technical Manual (Acorn Microcomputer), Acorn Computers — hosted on this wiki. CPU-card and keyboard-card parts lists: capacitor designators and values, and the note that the ten 0.1 µF decouplers may be substituted with 0.047 µF, and that the 15 µF electrolytics are polarised.