Acorn Archimedes A3000 Maintenance Guide

Acorn Archimedes A3000 main PCB (Issue 3, part 0180,000). The CMOS battery is at the bottom left, next to the four RISC OS ROMs; the ARM2, MEMC1a, VIDC1a and IOC are the large square packages.

This guide covers preventive maintenance for the Acorn Archimedes A3000 (the "BBC A3000", launched May 1989). The A3000 is an ARM2-based machine with the keyboard and motherboard in one case and an internal mains-powered switch-mode supply. Two maintenance points dominate everything else: the mains PSU (a genuine shock hazard) and the CMOS backup battery, which leaks and corrodes the board near the bottom-left corner.

⚠️ Safety: mains voltage inside the case

Unlike the 8-bit Acorn Atom and Acorn Electron, the A3000 carries a mains-powered switch-mode PSU inside the case. The Service Manual is explicit: dangerous voltages are exposed inside the case when the cover is removed; disconnect the computer from the mains before removing the cover.

• Unplug the mains lead before opening. The PSU is a separate cased module inside the unit; do not open or attempt to repair the PSU module.
• The PSU input voltage is set by a link wire to the pin marked 240 (or 120) on the supply. If the link is changed, label the new voltage on the case and fit the correct mains plug.
• Observe anti-static precautions for the ARM2, MEMC1a, VIDC1a, IOC and the DRAMs.

Identifying your board

The A3000 main PCB is marked with a part number and issue. Two are common: 0280,000 Issue A (early boards, with the VL2333-QC ARM2) and 0180,000 Issue 3 (later boards, VL86C010-10QC ARM2).

Acorn A3000 main components

Function	Device	Designator
CPU	ARM2 (VL2333-QC / VL86C010-10QC) @ 8 MHz	IC37
Memory controller	MEMC1a (VL2304A / VL86C310)	IC44
Video controller	VIDC1a (VL2303A "Arabella" / VL86C110)	—
I/O controller	IOC (VL2311 / VL86C410)	IC13
Keyboard controller	Intel 8051	—
Floppy controller	VLSI VL1772-02PC	—
DRAM (1 MB)	8 devices, in pairs by address	IC20–IC27
RISC OS 2 ROMs	4 × ROM (512 KB)	IC14–IC17
Master clock	24 MHz crystal	X3 (osc IC47, test point LK28)

⚠️ The CMOS battery: check it first

The A3000 keeps its configuration and clock in battery-backed CMOS RAM. The backup cell sits at the bottom-left corner of the board. Aged cells leak, and the electrolyte corrodes the nearby tracks and the bottom-left corner of the PCB — on at least one documented A3000 this corrosion was the reason the machine no longer worked.

• Inspect the bottom-left corner for green/white corrosion or a crusty residue around the battery.
• If the battery has leaked, neutralise the residue, clean the area with isopropyl alcohol, check the affected tracks for continuity, and repair any broken tracks before refitting power.
• Replace the cell pre-emptively on any machine that still has its original battery. Loss of configuration, a wrong clock, or boot problems are the usual symptoms of a flat or removed cell.

Opening the case

1. Unplug the mains lead and all peripherals.
2. Remove the case screws and lift the top cover. The PSU module is at the top left and the floppy drive at the top right; the keyboard is part of the lower assembly, connected to the main PCB by a ribbon.
3. To reach the full motherboard, disconnect the keyboard ribbon, the speaker leads and the PSU connector. Note orientations before unplugging.

Regular cleaning

• Brush and air-blow dust from the board, the PSU vents and the floppy mechanism.
• Clean the rear podule and mini-podule edge connectors with a soft eraser or contact cleaner; clean the monitor, parallel and (if fitted) serial sockets with contact cleaner on a foam swab.
• Clean the mouse/keyboard connectors. The A3000 mouse socket is on the underside.

Floppy drive

The A3000 uses a one-inch-high 3.5-inch drive (Citizen OSDC-65C), 1 MB unformatted (800 KB ADFS), with a 3 ms track-to-track step and a 4-pin power feed (+5 V, ground). Clean the head with isopropyl alcohol on a foam swab; replace the drive belt only if the specific drive uses one and it has perished. Most A3000 "won't read discs" faults are a dirty head or a marginal disc rather than the controller.

Power supply checks

With the mains hazard in mind, the only routine live measurement is the +5 V rail (a DC voltmeter on the PSU output connector, lid open, mains live — take care):

A3000 PSU output (per Service Manual)

Parameter	Value
Output voltage (V01)	4.9–5.1 V (nominal 5 V)
Output current	up to 4.4 A
Ripple and noise	50 mV pk-pk (0–50 MHz)
Over-voltage trip	5.8–7.0 V
Total output power	22 W continuous (29 W surge)

If the +5 V is low, high or absent, or shows excessive ripple, the fault is in the PSU module. The Service Manual treats the PSU as a non-serviceable assembly; replacement or a careful recap (see Acorn Archimedes A3000 Capacitor Guide) are the options.

Capacitor health

The A3000 main board uses leaded aluminium electrolytics and tantalums plus surface-mount ceramic decouplers; the PSU module has its own electrolytics and mains-side suppression capacitors. None of the board electrolytics are the leaking surface-mount type found on the later Acorn Archimedes A5000 and Risc PC, so the board itself ages gently — the battery and the PSU are the priorities. Full designator list and procedure: Acorn Archimedes A3000 Capacitor Guide.

Common failure points

Acorn A3000 — failure-prone items

Item	Symptom	Action
CMOS backup battery	Lost configuration/clock; corrosion at bottom-left	Replace cell; clean and repair corroded tracks
PSU module	Dead, random resets, out-of-spec +5 V, ripple	Check +5 V; recap or replace the PSU module
Podule / mini-podule edge connectors	Expansion unreliable	Clean fingers; reseat
ROM sockets (IC14–IC17)	Fails to initialise after a ROM swap	Reseat; check for bent pins / damaged tracks
DRAM (IC20–IC27)	Corrupt display, crashes	See test-ROM memory test in the troubleshooting guide

Recommended tools

• Posidrive/Philips screwdrivers and an anti-static strap.
• DC multimeter (for the +5 V check); an oscilloscope is needed for clock/bus diagnosis.
• Isopropyl alcohol, foam swabs, soft eraser and contact cleaner.
• Replacement CMOS battery and holder.
• Temperature-controlled soldering iron and solder wick for battery/track repair.

See Recommended Tools for the general toolkit.

Preventive maintenance checklist

1. Inspect and (if leaked) clean the CMOS battery corner; replace the cell.
2. Verify the +5 V rail and check for ripple.
3. Reseat the ROMs and clean the podule edge connectors.
4. Clean the floppy head; verify disc access.
5. Consider a PSU recap if the supply shows ripple (Acorn Archimedes A3000 Capacitor Guide).

Related pages

• Acorn Archimedes A3000
• Acorn Archimedes A3000 Troubleshooting Guide
• Acorn Archimedes A3000 Capacitor Guide
• Acorn Archimedes A4000 — the later ARM250 machine
• Acorn A3000 Service Manual · Acorn A3000 Technical Reference Manual
• Capacitor Failure Symptoms · Recommended Tools