Acorn Archimedes A3020 Maintenance Guide

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 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. After any internal work on mains-earthed equipment, Acorn requires the earth-continuity and DC-insulation (class 1) safety tests to be re-applied.

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. The socketed devices are the two RISC OS ROMs and, where fitted, the 2 MB RAM upgrade in the ZIP DRAM sockets.

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.

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. On any unrestored machine:

1. Remove the battery immediately, before it does any more damage.
2. Neutralise residue (white vinegar for the alkaline electrolyte), then rinse the area with high-strength isopropyl alcohol.
3. Inspect and buzz out every track around the battery, the floppy connector, the parallel port and the nearby resistor packs; repair any broken track.
4. 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.

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.

Opening and cleaning

1. Unplug the mains lead and all peripherals.
2. Remove the case screws and lift the top. Disconnect the floppy and (if fitted) hard-disc data and power cables to free the board.
3. Brush and air-blow dust from the board, the hard disc and the floppy mechanism.
4. 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. 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). Acorn's "action if PSU fails" routine is the safe way to diagnose a power problem:

1. Switch off and unplug the mains lead.
2. Check the 5 A fuse in the mains plug. If a replacement blows on switch-on, the supply is faulty.
3. Check the internal fuse FS1.
4. Confirm the drive-power links LK1 and LK2 are fitted.
5. 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 A5000, the A4 laptop and the Risc PC — so recap only what is visibly aged rather than doing a blanket board recap. 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. After any repair the earth-continuity and DC-insulation safety tests must be re-applied because the A3020 is mains-earthed equipment.

Common failure points

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

1. Remove and replace the NiCd battery; neutralise and repair any corrosion.
2. Check the plug fuse and FS1; verify the +5 V and +12 V rails and links LK1/LK2.
3. Clean the mini-podule and network edge connectors and the floppy head.
4. Back up and assess the IDE hard disc.
5. 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