Acorn System 4 Capacitor Replacement Guide: Difference between revisions
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* '''VDU, RAM, floppy-controller, Econet and interface cards''' — each has its own regulator electrolytic plus decouplers. | * '''VDU, RAM, floppy-controller, Econet and interface cards''' — each has its own regulator electrolytic plus decouplers. | ||
== | == Mains power supply == | ||
The System 4's integral PSU is mains-powered and contains the bulk smoothing electrolytics (and mains-side suppression parts). '''Disconnect the mains lead and discharge the bulk capacitor before any PSU work.''' Recap the PSU only if competent with mains supplies; otherwise replace the unit. Read each value from the fitted part. | The System 4's integral PSU is mains-powered and contains the bulk smoothing electrolytics (and mains-side suppression parts). '''Disconnect the mains lead and discharge the bulk capacitor before any PSU work.''' Recap the PSU only if competent with mains supplies; otherwise replace the unit. Read each value from the fitted part. | ||
Revision as of 10:50, 27 September 2026
This guide covers recapping the Acorn System 4 (1980). As a Eurocard rack it has per-card capacitors (a regulator electrolytic plus ceramic decouplers on each card), and as a cased machine it also has bulk smoothing electrolytics in its integral mains power supply.[1]
Per-card capacitors
On each Eurocard the recap target is the +5 V regulator electrolytic; the ceramic decouplers are stable and left in place. Read each electrolytic's value from the card and its circuit diagram and fit a 105 °C low-ESR part of equal capacitance and equal-or-higher voltage, observing polarity.
- CPU card — the Acorn System 1 card: a 15 µF/16 V electrolytic (see Acorn System 1 Capacitor Replacement Guide).
- VDU, RAM, floppy-controller, Econet and interface cards — each has its own regulator electrolytic plus decouplers.
Mains power supply
The System 4's integral PSU is mains-powered and contains the bulk smoothing electrolytics (and mains-side suppression parts). Disconnect the mains lead and discharge the bulk capacitor before any PSU work. Recap the PSU only if competent with mains supplies; otherwise replace the unit. Read each value from the fitted part.
Procedure (per card)
- Power off; remove the card from the backplane.
- Record each electrolytic's value, voltage and polarity.
- Desolder, clean the holes, fit the new part with correct polarity, solder and trim.
- Verify +5 V on the card and refit.
Related pages
- Acorn System 4
- Acorn System 4 Maintenance Guide
- Acorn System 4 Troubleshooting Guide
- Acorn System 1 Capacitor Replacement Guide · Capacitor Failure Symptoms
References
- ↑ Acorn System Catalogue and Acorn System 1 Technical Manual, Acorn Computers — hosted on this wiki. Source for the Eurocard set and the System 1 card capacitor values.