Editing Acorn Archimedes A3020 Maintenance Guide

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[[File:Acorn Archimedes A3020 motherboard.jpg|thumb|360x360px|Acorn A3020 "Heron E" main PCB (0194,500). The ARM250 is the large square package centre-board; the RISC OS ROM is above it, the 2.5-inch IDE hard disc sits top-right, and the on-board mains PSU (transformer and red suppression capacitor) is at the left edge.]]

This guide covers preventive maintenance for the '''[[Acorn Archimedes A3020]]''' (ARM250 "Heron E" board, part 0194,500). The A3020 is a single-box machine with an on-board mains power supply, an optional internal 2.5-inch IDE hard disc, and a highly integrated board with few serviceable parts. The three maintenance priorities are the '''NiCd backup battery''', the '''on-board PSU''', and the ageing '''hard disc'''.

== ⚠️ Safety: on-board mains PSU ==

Unlike the [[Acorn Archimedes A4000|A4000]], whose PSU is a separate cased module, the A3020's mains power supply is built directly onto the main PCB. '''The board carries mains voltages. Disconnect the mains lead before opening the case,''' and treat the PSU section of the board as live-hazard until proven discharged.<ref name="sm">[[Acorn A3010, A3020 and A4000 Service Manual]], Acorn Computers Ltd — hosted on this wiki. Source for the PSU-fail and main-PCB-fail routines, the 5 A mains fuse and internal fuse FS1, thermal-shutdown behaviour, the +5 V and +12 V rails, the drive-power links LK1/LK2, the functional test suite and the earth-continuity / DC-insulation safety tests.</ref> After any internal work on mains-earthed equipment, Acorn requires the earth-continuity and DC-insulation (class 1) safety tests to be re-applied.<ref name="sm" />

== The machine and its board ==

The ARM250 integrates the ARM2 core, MEMC1a, VIDC1a and IOC into one 12 MHz package, so there are no socketed processor-family chips to reseat or swap.<ref name="chris">Whytehead, Chris. [https://chrisacorns.computinghistory.org.uk/Computers/A3020.html "Acorn A3020"], Chris's Acorns / The Centre for Computing History.</ref> The socketed devices are the two RISC OS ROMs and, where fitted, the 2 MB RAM upgrade in the ZIP DRAM sockets.

{| class="wikitable styled-table" style="width:90%; text-align:center;"
|+'''Acorn A3020 key facts'''
! Item !! Detail
|-
| Processor || ARM250 @ 12 MHz (ARM2 + MEMC1a + VIDC1a + IOC)
|-
| RAM || 2 MB standard; 4 MB with a ZIP DRAM upgrade board
|-
| ROM || RISC OS 3.11 (two devices)
|-
| Storage || 3.5" floppy (1.6 MB) + optional 2.5" IDE hard disc
|-
| Expansion || one mini-podule slot; separate network-interface slot
|-
| PSU || built onto the main PCB (+5 V, +12 V)
|-
| Board || 0194,500 "Heron E"
|}

== ⚠️ The backup battery — do this first ==

The A3020 keeps its configuration and clock in battery-backed CMOS RAM. The cell is a '''rechargeable NiCd barrel, 1.2 V 280 mAh (Varta, Acorn part 0817.014)''', soldered to the top-right corner of the board, directly under the floppy drive.<ref name="trm">[[Acorn A3010, A3020 and A4000 Technical Reference Manual]], Acorn Computers Ltd — hosted on this wiki. Battery part, RTC device (PCF8583), reset links and per-designator board values.</ref><ref name="celso">[https://celso.io/posts/2025/11/15/acorn-a3020/ "Repairing an Acorn A3020"], celso.io (restoration write-up: broken tracks from battery leakage, dead floppy and IDE, corroded parallel port and resistor packs, PSU transformer-pin repair).</ref>

This cell leaks corrosive electrolyte even in storage, and the leakage is the single most common cause of a dead A3020. It attacks the tracks, vias, IC legs, sockets and the RF shield around the battery, and because the floppy connector sits over the battery it frequently takes out the floppy and, on hard-disc machines, the IDE drive as well.<ref name="celso" /> On any unrestored machine:

# '''Remove the battery immediately''', before it does any more damage.
# Neutralise residue (white vinegar for the alkaline electrolyte), then rinse the area with high-strength isopropyl alcohol.
# Inspect and buzz out every track around the battery, the floppy connector, the parallel port and the nearby resistor packs; repair any broken track.
# Fit a replacement using a coin-cell holder (for example a CR2032) '''with a series diode''' so the non-rechargeable cell cannot be back-charged by the board.<ref name="celso" /><ref name="retrorr">[https://retrorepairsandrefurbs.com/2024/09/27/1992-acorn-archimedes-3010-repair-restoration/ "1992 Acorn Archimedes A3010 repair/restoration"], Retro Repairs and Refurbs (battery leakage, PCF8583 RTC, track repair, CR2032 conversion).</ref>

The RTC device most often killed by the leak is the '''PCF8583''' clock/calendar chip; if it cannot be read the machine will not reach the desktop.<ref name="retrorr" /><ref name="trm" />

== Opening and cleaning ==

# Unplug the mains lead and all peripherals.
# Remove the case screws and lift the top. Disconnect the floppy and (if fitted) hard-disc data and power cables to free the board.<ref name="chris" />
# Brush and air-blow dust from the board, the hard disc and the floppy mechanism.
# Clean the mini-podule and network-interface edge connectors with a soft eraser; clean the keyboard, parallel, serial and video sockets with contact cleaner on a foam swab.

== Hard disc ==

Hard-disc A3020s use a 2.5-inch IDE drive (60 MB at launch, 80 MB on later education machines). After decades the usual faults are mechanical — a drive that will not spin up, or growing noise before failure. If replacing the drive, note that the RISC OS 3.1 IDE filing system limits usable capacity to about 512 MB, so a large modern drive, CompactFlash or SD adapter needs a partition kept within that limit or third-party software.<ref name="trm" /> Back up the original drive where it still reads.

== Power supply checks ==

The on-board PSU delivers +5 V (logic, floppy and hard disc) and +12 V (the hard disc and video-connector pin 12).<ref name="sm" /> Acorn's "action if PSU fails" routine is the safe way to diagnose a power problem:

# Switch off and unplug the mains lead.
# Check the '''5 A fuse in the mains plug'''. If a replacement blows on switch-on, the supply is faulty.
# Check the internal fuse '''FS1'''.
# Confirm the drive-power links '''LK1''' and '''LK2''' are fitted.
# If the supply runs then cuts out, suspect thermal shutdown — check ventilation and the load; repeated shutdowns mean a faulty supply.

Because the PSU is part of the main board, a PSU-section repair is a board-level electronics job carried out with the mains lead disconnected and the primary bulk capacitor discharged — see the [[Acorn Archimedes A3020 Capacitor Guide]].

== Capacitor health ==

The A3020 board is mostly leaded electrolytics with a small number of surface-mount aluminium electrolytics and surface-mount ceramic decouplers. It is '''not''' one of the Acorn machines that suffer routine surface-mount electrolyte leakage — those are the [[Acorn Archimedes A5000|A5000]], the A4 laptop and the Risc PC — so recap only what is visibly aged rather than doing a blanket board recap.<ref name="stardot">[https://stardot.org.uk/forums/viewtopic.php?t=10675 "Which Acorn machines leak"], Stardot forums (the leakage problem is specific to the SMD-electrolytic machines; the battery is the usual corrosion source on the A30x0).</ref> Full detail: [[Acorn Archimedes A3020 Capacitor Guide]].

== Functional and safety testing ==

Acorn's service procedure uses the ARM250 functional test software (the "dealer test disc"), which exercises the audio, battery-backed RAM, floppy, IDE hard-disc, external-port, keyboard/mouse, memory, real-time-clock and video subsystems and produces a test report.<ref name="sm" /> After any repair the earth-continuity and DC-insulation safety tests must be re-applied because the A3020 is mains-earthed equipment.<ref name="sm" />

== Common failure points ==

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Acorn A3020 — failure-prone items'''
! Item !! Symptom !! Action
|-
| NiCd battery (top-right, under floppy) || Lost config/clock; corrosion; dead floppy or IDE || Remove, neutralise, repair tracks, fit CR2032 + series diode
|-
| PCF8583 RTC || Machine will not reach the desktop || Replace if killed by battery leakage
|-
| On-board PSU || Dead, random resets, thermal shutdown || Check plug fuse and FS1; discharge and recap the PSU section
|-
| 2.5" IDE hard disc || Won't spin up, noisy, boot errors || Mechanical failure; replace (mind the ~512 MB RISC OS 3.1 limit)
|-
| Mini-podule / network edge connectors || Expansion or network unreliable || Clean fingers; reseat
|-
| ARM250 || No combination of CPU/memory/video works || Whole-device replacement (no socketed sub-chips)
|}

== Recommended tools ==

* Posidrive/Philips screwdrivers and an anti-static strap.
* DC multimeter for rail checks; oscilloscope for bus-level diagnosis.
* Isopropyl alcohol, white vinegar (battery neutralising), foam swabs, soft eraser, contact cleaner.
* CR2032 holder and a small-signal diode for the battery conversion.
* Fine-tip temperature-controlled soldering iron and solder wick.
* Earth-continuity and insulation testers if returning the machine to service.

See [[Recommended Tools]] for the general toolkit.

== Preventive maintenance checklist ==

# Remove and replace the NiCd battery; neutralise and repair any corrosion.
# Check the plug fuse and FS1; verify the +5 V and +12 V rails and links LK1/LK2.
# Clean the mini-podule and network edge connectors and the floppy head.
# Back up and assess the IDE hard disc.
# Re-apply the earth-continuity and insulation safety tests after any internal work.

== Related pages ==

* [[Acorn Archimedes A3020]]
* [[Acorn Archimedes A3020 Troubleshooting Guide]]
* [[Acorn Archimedes A3020 Capacitor Guide]]
* [[Acorn Archimedes A4000 Maintenance Guide]] — three-box sibling with a separate PSU module
* [[Acorn A3010, A3020 and A4000 Service Manual]] · [[Acorn A3010, A3020 and A4000 Technical Reference Manual]]
* [[Capacitor Failure Symptoms]] · [[Recommended Tools]]

== References ==

<references />

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