Editing Acorn Archimedes A3000 Maintenance Guide

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[[File:Acorn Archimedes A3000 motherboard.jpg|thumb|360x360px|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.'''<ref name="sm">[[Acorn A3000 Service Manual]], Acorn Computers &mdash; hosted on this wiki. Source for the PSU performance figures (output 4.9&ndash;5.1&nbsp;V, up to 4.4&nbsp;A, 22&nbsp;W continuous, 50&nbsp;mV pk-pk ripple, over-voltage threshold 5.8&ndash;7.0&nbsp;V), the 240/120&nbsp;V mains-selector link, the mains-hazard warning, the full PCB parts list, the test points, and the fault-diagnosis procedures.</ref>

* Unplug the mains lead before opening, and never work on the supply while it is plugged in. The PSU is a separate cased module inside the unit; its primary side and reservoir and mains-suppression capacitors '''can hold a lethal charge after the machine is unplugged'''. The module can be opened and recapped as part of a restoration (see the [[Acorn Archimedes A3000 Capacitor Guide]]), but only if you are competent with mains switch-mode supplies &mdash; discharge the reservoir capacitor and confirm 0&nbsp;V before touching the primary side.
* 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.<ref name="sm" />
* 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&nbsp;A''' (early boards, with the VL2333-QC ARM2) and '''0180,000 Issue&nbsp;3''' (later boards, VL86C010-10QC ARM2).<ref name="chris">Whytehead, Chris. [https://chrisacorns.computinghistory.org.uk/Computers/A3000.html "BBC A3000"], Chris's Acorns / The Centre for Computing History. Source for the board issues (0280,000 Issue A, 0180,000 Issue 3), the chip set (ARM2, MEMC1a, VIDC1a "Arabella", IOC, Intel 8051 keyboard controller, VL1772 FDC), the battery-corrosion observation, the model list (AKB01 etc.) and the Citizen OSDC-65C drive.</ref>

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{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Acorn A3000 main components'''
! Function !! Device !! Designator
|-
| CPU || ARM2 (VL2333-QC / VL86C010-10QC) @ 8&nbsp;MHz || IC37
|-
| Memory controller || MEMC1a (VL2304A / VL86C310) || IC44
|-
| Video controller || VIDC1a (VL2303A "Arabella" / VL86C110) || &mdash;
|-
| I/O controller || IOC (VL2311 / VL86C410) || IC13
|-
| Keyboard controller || Intel 8051 || &mdash;
|-
| Floppy controller || VLSI VL1772-02PC || &mdash;
|-
| DRAM (1&nbsp;MB) || 8 devices, in pairs by address || IC20&ndash;IC27
|-
| RISC OS 2 ROMs || 4 × ROM (512&nbsp;KB) || IC14&ndash;IC17
|-
| Master clock || 24&nbsp;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 &mdash; on at least one documented A3000 this corrosion was the reason the machine no longer worked.<ref name="chris" />

* 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 ==

# Unplug the mains lead and all peripherals.
# 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.<ref name="chris" />
# 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&nbsp;MB unformatted (800&nbsp;KB ADFS), with a 3&nbsp;ms track-to-track step and a 4-pin power feed (+5&nbsp;V, ground).<ref name="sm" /> 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&nbsp;V rail (a DC voltmeter on the PSU output connector, lid open, mains live &mdash; take care):

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{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''A3000 PSU output (per Service Manual)'''
! Parameter !! Value
|-
| Output voltage (V01) || 4.9&ndash;5.1&nbsp;V (nominal 5&nbsp;V)
|-
| Output current || up to 4.4&nbsp;A
|-
| Ripple and noise || 50&nbsp;mV pk-pk (0&ndash;50&nbsp;MHz)
|-
| Over-voltage trip || 5.8&ndash;7.0&nbsp;V
|-
| Total output power || 22&nbsp;W continuous (29&nbsp;W surge)
|}

If the +5&nbsp;V is low, high or absent, or shows excessive ripple, the fault is in the PSU module. Acorn's manual treated the PSU as an exchange unit, but with replacements long unavailable the usual fix is a careful recap of the module (see [[Acorn Archimedes A3000 Capacitor Guide]]) &mdash; discharge the reservoir capacitor and confirm 0&nbsp;V before touching the primary side, as it can hold a lethal charge after unplugging.

== 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 &mdash; the battery and the PSU are the priorities. Full designator list and procedure: [[Acorn Archimedes A3000 Capacitor Guide]].

== Common failure points ==

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{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Acorn A3000 &mdash; 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&nbsp;V, ripple || Check +5&nbsp;V; recap or replace the PSU module
|-
| Podule / mini-podule edge connectors || Expansion unreliable || Clean fingers; reseat
|-
| ROM sockets (IC14&ndash;IC17) || Fails to initialise after a ROM swap || Reseat; check for bent pins / damaged tracks
|-
| DRAM (IC20&ndash;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&nbsp;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 ==

# Inspect and (if leaked) clean the CMOS battery corner; replace the cell.
# Verify the +5&nbsp;V rail and check for ripple.
# Reseat the ROMs and clean the podule edge connectors.
# Clean the floppy head; verify disc access.
# 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]] &mdash; the later ARM250 machine
* [[Acorn A3000 Service Manual]] · [[Acorn A3000 Technical Reference Manual]]
* [[Capacitor Failure Symptoms]] · [[Recommended Tools]]

== References ==

<references />

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[[Category:Acorn Computers]]
[[Category:Maintenance Guides]]