Acorn System 4 Maintenance Guide

This guide covers preventive maintenance for the Acorn System 4 (1980), a double-height Eurocard rack with a 14-slot lower frame and two floppy drives in the upper half. Its maintenance is the System 3 work (cards plus floppy mechanism) scaled to the larger frame, plus the integral mains power supply.^[1]

⚠️ Safety: integral mains PSU

The cased System 4 contains a mains-powered power supply feeding the backplane. Disconnect the mains lead before opening, and treat the PSU primary side as live. The Eurocards themselves carry low-voltage rails only, and there is no CRT.

Cards and frame

A minimum System 4 has a 1 MHz 6502 CPU card, a VDU card, 16 KB of RAM and a floppy-disc controller (Intel 8271) with two drives in the top of the rack; the 14-slot lower frame leaves room for many more Eurocards.^[1] A documented System 4 fit includes the CPU card (with a System keyboard connector), an 8 KB static RAM card, a 40-column VDU card, an Econet card, a Universal Interface Board and a Bus Extender — a typical Econet file-server build.^[2]

Maintenance

Backplane and edge connectors: the 14-slot backplane has many contacts — clean each card's fingers and the backplane sockets, and reseat firmly. This is the leading cause of intermittent faults on a large rack.
Per-card +5 V: verify the rail on each card; confirm regulator heatsinks.
Floppy drives: two 5.25-inch drives in the upper frame — clean the heads, check the belts and the ribbon cable to the FDC card (see Acorn System 3 Maintenance Guide).
Econet: if fitted as a file server, clean the Econet connectors and check the network termination.
Cooling and PSU: keep the frame ventilated; inspect the mains PSU for ageing.

Capacitor health

Each Eurocard carries a regulator electrolytic plus ceramic decouplers, and the integral mains PSU has bulk smoothing electrolytics. See Acorn System 4 Capacitor Replacement Guide.

Preventive maintenance checklist

Clean the 14-slot backplane and each card's edge fingers; reseat all cards.
Verify +5 V on each card.
Clean both floppy heads; check belts and the FDC ribbon.
Check the Econet connectors (if a file server).
Inspect the mains PSU; consider its electrolytics (mains caution).

Related pages

References

↑ ^1.0 ^1.1 Acorn System Catalogue and Acorn System 1 Technical Manual, Acorn Computers — hosted on this wiki. Source for the Eurocard set, the 14-slot frame, the Intel 8271 floppy controller, and the per-card +5 V regulators.
↑ Whytehead, Chris. "Acorn System 4", Chris's Acorns / The Centre for Computing History. Source for the example card set and the 14-slot backplane.

[cat-1] 1.0 ^1.1 Acorn System Catalogue and Acorn System 1 Technical Manual, Acorn Computers — hosted on this wiki. Source for the Eurocard set, the 14-slot frame, the Intel 8271 floppy controller, and the per-card +5 V regulators.

[chris4-2] Whytehead, Chris. "Acorn System 4", Chris's Acorns / The Centre for Computing History. Source for the example card set and the 14-slot backplane.

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