Acorn System 5 Capacitor Replacement Guide

Acorn System 5 Eurocard rack with two floppy drives.

This guide covers recapping the Acorn System 5 (late 1982). As a Eurocard rack it has per-card capacitors (a regulator electrolytic plus ceramic decouplers on each card), and as a fully-cased machine it also has bulk smoothing electrolytics in its integral mains power supply. The Acorn System 5 Handbook documents the boards.

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 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 (6502 or 6502A) — regulator electrolytic plus decouplers (the 1 MHz 6502 card follows the Acorn System 1 values).
• VDU card (80×25 or 40×25) — regulator electrolytic plus decouplers.
• 32 KB DRAM cards — regulator electrolytic plus decouplers; the DRAM cards draw the most current, so their regulator electrolytics are worth checking first.
• Floppy-controller and Econet cards — regulator electrolytic plus decouplers.

⚠️ Mains power supply

The System 5'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 it. Read each value from the fitted part.

Procedure (per card)

1. Power off; remove the card from the backplane.
2. Record each electrolytic's value, voltage and polarity.
3. Desolder, clean the holes, fit the new part with correct polarity, solder and trim.
4. Verify +5 V on the card and refit.

Related pages

• Acorn System 5
• Acorn System 5 Maintenance Guide
• Acorn System 5 Troubleshooting Guide
• Acorn System 1 Capacitor Replacement Guide · Capacitor Failure Symptoms