Editing Acorn A5000 Maintenance Guide

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[[File:Acorn A5000 motherboard.jpg|thumb|360x360px|Acorn A5000 motherboard (25 MHz, board 0192,100). Four RISC OS 3 ROMs (with an empty fifth socket), the ARM3, MEMC1a, VIDC1a and IOC, the IDE/floppy connectors at lower right, the podule-backplane connector, and the battery pack.]]

This guide covers preventive maintenance for the '''[[Acorn Archimedes A5000]]''' (launched September 1991). The A5000 is an ARM3 machine with a surface-mount main board, an internal mains switch-mode PSU, and an internal IDE hard disc. Three things dominate A5000 maintenance: the '''mains PSU''', the '''rechargeable battery pack''' (which leaks), and the '''surface-mount electrolytic capacitors''' (which also leak and corrode the board).

== ⚠️ Safety: mains PSU ==

The A5000 contains a fan-cooled mains switch-mode PSU. The Service Manual prohibits opening or repairing it: '''under no circumstances should any attempt be made to repair or modify the PSU''' &mdash; exchange it as a unit, because opening it invalidates the safety tests applied at manufacture.<ref name="sm">[[Acorn A5000 Service Manual]] (Module Level Service Manual, Issue 1, November 1991), Acorn Computers &mdash; hosted on this wiki. Source for the PSU-fail procedure (5&nbsp;A mains fuse; 5&nbsp;V feeds the main PCB/floppy/hard disc, &minus;5&nbsp;V feeds the backplane, +12&nbsp;V feeds the video connector SK1 pin&nbsp;12), the DRAM-size links, the functional test suite (A5000 test disc 0292,824), and the earth-continuity / DC-insulation safety tests.</ref> Disconnect the mains lead before opening, and re-apply the earth-continuity and DC-insulation (class&nbsp;1) safety tests after any internal work, because the A5000 is mains-earthed equipment.<ref name="sm" />

== The machine ==

The A5000 was Acorn's mid-range ARM3 machine, an offshoot of the [[Acorn A4]] portable project. It introduced several changes over the earlier Archimedes and A3000: a 15-pin VGA monitor connector (replacing the 9-pin RGB), a PC-standard serial port (replacing RS423), a bidirectional parallel port, a high-density floppy (the Acorn 1.6&nbsp;MB F format, plus MS-DOS 1.44&nbsp;MB), and an on-board IDE controller (replacing the ST506/MFM interface). It was the first Acorn computer to ship with RISC OS 3.<ref name="chris">Whytehead, Chris. [https://chrisacorns.computinghistory.org.uk/Computers/A5000.html "Acorn A5000"], Chris's Acorns / The Centre for Computing History. Source for the feature changes, the model list (ALB10&ndash;ALB55, ALC10/20), the RISC OS 3.00 ADFSBuffers bug, the 25/33&nbsp;MHz (Alpha) split, the board part numbers (0192,100; 0192,420), VIDC1a (VL2303A), the battery pack, and the motherboard photographs.</ref>

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{| class="wikitable styled-table" style="width:90%; text-align:center;"
|+'''Acorn A5000 key facts'''
! Item !! Detail
|-
| Processor || ARM3 @ 25&nbsp;MHz (4&nbsp;KB cache); 33&nbsp;MHz on the 1993 "Alpha"
|-
| Support chips || MEMC1a, VIDC1a (VL2303A), IOC
|-
| RAM || 2&nbsp;MB or 4&nbsp;MB (one MEMC1a addresses 4&nbsp;MB; 8&nbsp;MB needs a second MEMC1a, Alpha only)
|-
| ROM || RISC OS 3 (2&nbsp;MB; four ROMs + an unused fifth socket)
|-
| Storage || HD floppy (1.6&nbsp;MB) + on-board IDE hard disc
|-
| I/O || PC-style Super I/O (IDE, floppy, serial, parallel); 15-pin VGA; bidirectional parallel
|-
| Expansion || 4-podule backplane (0192,004)
|-
| Option || FPA10 floating-point accelerator (socketed, near the battery)
|-
| PSU || internal fan-cooled mains switch-mode module
|}

== ⚠️ The battery pack: check it first ==

The A5000 keeps its configuration and clock in CMOS RAM, backed by a '''rechargeable battery pack''' on the board, near the FPA socket.<ref name="chris" /> These packs leak with age, and the electrolyte corrodes the surrounding tracks. Inspect the pack on any unrestored machine; if it has leaked, remove it, neutralise and clean the residue with isopropyl alcohol, check the nearby tracks for continuity, and repair any breaks before refitting power. Replace the pack (period packs can be substituted with a modern cell and holder, or a CR2032 + diode/holder modification). Lost configuration, a wrong clock, or boot problems point to a flat or removed pack.

== ⚠️ Surface-mount capacitor leakage ==

The A5000 main board is surface-mount, and its small surface-mount aluminium electrolytic capacitors are the machine's defining long-term fault. As they age the electrolyte escapes and corrodes the pads and tracks beneath and around each capacitor, which causes intermittent and progressive faults (corrupted RAM control lines, loss of sound, instability and outright failure to start).<ref name="sm" /> On any A5000 that has not been recapped, plan to replace the surface-mount electrolytics and clean the board; full procedure and the verified data available: [[Acorn A5000 Capacitor Guide]].

== Opening and cleaning ==

# Unplug the mains lead and peripherals.
# Remove the cover. The PSU is at one rear corner, with the floppy and hard disc on a removable drive tray.<ref name="chris" />
# Lift the drive tray (it hooks into slots on the case sides and is held by a single screw) to reach the board; disconnect the IDE, floppy and power cables first.<ref name="chris" />
# Brush and air-blow dust from the board, the PSU fan and vents, and the drives. Keep the PSU fan aperture clear &mdash; the Service Manual notes a blocked aperture as a cause of PSU shutdown.<ref name="sm" />
# Clean the four podule backplane connectors and the monitor, serial and parallel sockets with contact cleaner.

== Hard disc ==

The internal IDE drives (Conner, Fujitsu and others, from 40&nbsp;MB up) are now decades old and the usual faults are mechanical (failure to spin up, bearing noise). When fitting a replacement, RISC OS 3.1's IDE filing system limits usable capacity to roughly 512&nbsp;MB; larger drives, CompactFlash or SD adapters need third-party software. Back up the original drive where possible.

== Power supply checks ==

The PSU is a sealed module; the safe diagnosis is the Service Manual's "action if PSU fails" routine:<ref name="sm" />

# Switch off and unplug the mains lead. Check the '''5&nbsp;A fuse in the mains plug'''. If a new fuse blows on switch-on, the PSU is faulty &mdash; exchange it.
# For an individual rail failure, check the rails at the faston power connectors: '''+5&nbsp;V''' (main PCB, floppy, hard disc), '''&minus;5&nbsp;V''' (backplane), '''+12&nbsp;V''' (video connector SK1 pin&nbsp;12, and the disc motors).
# If the PSU runs then shuts down, check the fan and the fan aperture; a failed fan or blocked aperture causes thermal shutdown. Repeated shutdowns mean a faulty PSU.

Do not open the PSU module.

== RISC OS version ==

The first A5000 models (ALB10/12/14) shipped with '''RISC OS 3.00''', which has a serious ADFSBuffers bug that can corrupt discs; on a 3.00 machine, set '''ADFSBuffers to 0''', or upgrade to RISC OS 3.10/3.11.<ref name="chris" /> Check the version with <code>*FX&nbsp;0</code> and upgrade ageing 3.00 ROMs to the stable 3.11 set.

== Common failure points ==

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{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Acorn A5000 &mdash; failure-prone items'''
! Item !! Symptom !! Action
|-
| Surface-mount electrolytics || Sound loss, RAM-control faults, instability, corrosion || Recap; clean residue; repair corroded tracks
|-
| Battery pack || Lost config/clock; corrosion near FPA socket || Clean, repair tracks, replace pack
|-
| Mains PSU module || Dead, random resets, fan/thermal shutdown || Check plug fuse; clear fan aperture; exchange PSU
|-
| IDE hard disc || Won't spin up, noisy, boot errors || Replace drive (mind the ~512&nbsp;MB RISC OS 3.1 limit)
|-
| RISC OS 3.00 ROMs || Disc corruption || Set ADFSBuffers 0 or upgrade to 3.11
|-
| Podule backplane / contacts || Expansion unreliable || Clean contacts; reseat backplane and podules
|}

== Recommended tools ==

* Posidrive/Philips screwdrivers and an anti-static strap.
* DC multimeter (rail checks); oscilloscope for bus-level work.
* '''Hot-air or fine-tip soldering equipment''' for the surface-mount recap, plus solder wick, flux and isopropyl alcohol.
* Replacement battery/holder; replacement IDE drive or solid-state adapter.
* Earth-continuity and insulation testers if returning the machine to service.

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

== Preventive maintenance checklist ==

# Inspect/replace the battery pack; clean any corrosion.
# Recap the surface-mount electrolytics and clean the board ([[Acorn A5000 Capacitor Guide]]).
# Check the plug fuse; verify +5&nbsp;V, &minus;5&nbsp;V and +12&nbsp;V; confirm the PSU fan runs.
# Confirm the RISC OS version; upgrade 3.00 or set ADFSBuffers 0.
# Clean the backplane contacts; back up and assess the IDE drive.
# Re-apply the safety tests after internal work.

== Related pages ==

* [[Acorn Archimedes A5000]]
* [[Acorn A5000 Troubleshooting Guide]]
* [[Acorn A5000 Capacitor Guide]]
* [[Acorn Archimedes A4000]] &mdash; the ARM250 sibling
* [[Acorn A5000 Service Manual]] · [[Acorn A5000 Circuit Diagrams]]
* [[Capacitor Failure Symptoms]] · [[Recommended Tools]]

== References ==

<references />

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