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Acorn System 2 Maintenance Guide

From RetroTechCollection
Acorn System 2 in a 19-inch card frame with an 8-slot backplane.

This guide covers preventive maintenance for the Acorn System 2 (1980), a rack-mounted Eurocard machine. The System 2 is a collection of Eurocards on an 8-slot backplane, so maintenance is largely per-card: edge-connector integrity, the on-card +5 V regulators, socket reseating, and the backplane and power supply.[1]

⚠️ Safety

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The Eurocards run on low-voltage rails from the backplane. If an Acorn mains power supply is fitted, that PSU contains mains voltage — disconnect the mains lead before working near it, and treat its primary side as live. The cards themselves carry no mains and no CRT.

Cards

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A typical System 2 has four Eurocards: the 1 MHz 6502 CPU card (with 2 KB Cassette Operating System), a 40×25 teletext VDU card (MC6845 + SAA5050), a cassette interface card, and a memory card (4 KB RAM + 4 KB Acorn System BASIC ROM).[1] The CPU and cassette cards are the same as the Acorn System 1; their maintenance is covered in the Acorn System 1 Maintenance Guide.

Maintenance

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  • Backplane and edge connectors: clean each card's EuroConnector fingers and the backplane sockets with a soft eraser or contact cleaner. Oxidised edge connectors are the most common cause of intermittent faults on a racked system. Reseat each card firmly.
  • On-card regulators: each card regulates its own +5 V with an LM340-type regulator. Verify +5 V on each card and confirm the regulator heatsinks are fitted.
  • IC reseating: the cards are socketed; reseat the 6502, ROMs, RAM and the VDU's MC6845/SAA5050.
  • VDU card: clean the video output connector; the 40×25 teletext display uses the SAA5050 character generator.
  • Cassette and keyboard: keep the cassette DIN socket and the external keyboard connector clean.

Capacitor health

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Each Eurocard carries ceramic decouplers plus a regulator electrolytic; the CPU and cassette cards use the System 1 values (a 15 µF/16 V electrolytic each). See Acorn System 2 Capacitor Replacement Guide.

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  • Screwdrivers and an anti-static strap; DC multimeter for the +5 V checks.
  • Contact cleaner and a soft eraser for the EuroConnectors and backplane.
  • Temperature-controlled soldering iron and solder wick for the per-card electrolytics.

See Recommended Tools for the general toolkit.

Preventive maintenance checklist

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  1. Clean the backplane sockets and each card's edge fingers; reseat all cards.
  2. Verify +5 V on each card; confirm regulator heatsinks.
  3. Reseat socketed ICs (6502, ROMs, RAM, MC6845/SAA5050).
  4. Clean the cassette DIN and keyboard connectors.
  5. If an Acorn mains PSU is fitted, inspect it (mains) and consider its electrolytics.
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References

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  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 per-card LM340-type +5 V regulators, and the CPU/cassette card detail shared with the Acorn System 1.


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