Acorn A5000 Troubleshooting Guide

This guide gives diagnosis for the Acorn Archimedes A5000 (ARM3, board 0192,100 / 0192,420). It follows the fault-finding and functional tests in the Acorn A5000 Service Manual, supported by the on-wiki Acorn A5000 Circuit Diagrams. The A5000 main board is surface-mount and Acorn treats it as a replacement-only assembly, so component-level work depends on the circuit diagrams and on recognising the board's two ageing-failure mechanisms: leaked surface-mount electrolytics and a leaked battery pack.^[1]

⚠️ Mains warning

The A5000 has a fan-cooled mains PSU. Disconnect the mains lead before removing the cover; never open the PSU module (exchange it); re-apply the earth-continuity and DC-insulation safety tests after any internal work.^[1]

Acorn A5000 main PCB circuit diagram, sheet 1 of 4 (Technical Reference Manual). All four sheets plus the power-and-ground sheet are on the wiki at Acorn A5000 Circuit Diagrams. (Source: The Centre for Computing History.)

First: power

Most "dead A5000" faults are the PSU or its fuse. Work the Service Manual sequence:^[1]

Switch off, unplug the mains lead. Check the 5 A fuse in the mains plug. Fit a new 5 A fuse; if it blows on switch-on, the PSU is faulty — exchange it.
Measure the rails at the faston power connectors:

**A5000 supply rails**
Rail	Feeds
+5 V	Main PCB, floppy drive, hard disc
−5 V	Backplane expansion connector
+12 V	Video connector SK1 pin 12; floppy/hard-disc motors

If the PSU runs then cuts out, check the fan and that the fan aperture is not blocked — a stalled fan or blocked aperture causes thermal shutdown. Repeated shutdowns mean a faulty PSU.^[1]

Dead computer with power present

If the rails are good but the machine is dead, the Service Manual's checks are:^[1]

Check the DRAM-size links are set correctly for the fitted memory (the combination of main-PCB DRAM and any RAM card must be a legal size — e.g. 4 MB on the main PCB plus a RAM card is illegal). See the links appendix.
Check the ZIP-package DRAM ICs are correctly seated in their sockets.
Check the ROMs are correctly located and oriented with no lifted pins.
Substitute the backplane and remove podules one at a time — a shorted podule or backplane can hold the machine down. Re-test with a known-good backplane.
The main PCB is a replacement-only assembly; a board fault that survives the above is returned/replaced.

Because the ARM3, MEMC1a, VIDC1a and IOC are separate devices on the A5000, the bus-level checks used on the A3000 (clock present, reset released, DRAM RAS/CAS, address lines toggling under a held reset, data bus not stuck) apply here using the Acorn A5000 Circuit Diagrams. As on every ARM2/ARM3 Archimedes, do not leave a board powered with no clock — the DRAM loses refresh.

Always suspect leaked electrolyte

On an A5000, intermittent and progressive faults are very often leaked surface-mount electrolytic capacitors rather than a failed IC. The escaping electrolyte is corrosive and attacks the pads and tracks beneath each capacitor, which produces faults such as corrupted RAM control lines, loss of sound, and instability.^[1] Before deep component diagnosis, inspect the board under magnification for crusty residue or discoloured pads around the surface-mount electrolytics, and around the battery pack. Recapping and cleaning often clears otherwise-baffling faults — see Acorn A5000 Capacitor Guide.

Functional tests (A5000 test disc)

For a machine that powers up but misbehaves, Acorn's functional test software (test disc 0292,824) isolates the fault by subsystem:^[1]

**A5000 functional tests and what they exercise**
Test	Exercises
Memory test	the 2 MB / 4 MB DRAM (and any RAM card)
Battery-backed RAM test	CMOS RAM and the battery-backed configuration
IDE hard disc interface test	the on-board IDE interface and drive
External port tests	serial, parallel and Econet (with a parallel-to-video loopback box)
Disc interface test	the floppy controller and drive (needs a scratch disc)
Real-time test	the real-time clock
Audio tests	the VIDC sound output and audio stage
Video tests	the VIDC video output and modes
Keyboard and mouse tests	the keyboard matrix and quadrature mouse
Hard disc exerciser / formatter	surface/seek behaviour; formatting

After repair, the Service Manual requires soak tests and the earth-continuity / DC-insulation safety tests.^[1]

Specific faults

Symptom	Probable cause	Action
Disc corruption, lost files	RISC OS 3.00 ADFSBuffers bug	On a 3.00 machine set ADFSBuffers 0, or upgrade to RISC OS 3.11
Lost configuration / wrong clock	Flat or leaked battery pack	Clean corrosion, repair tracks, replace pack
No / distorted sound	Leaked electrolytic in the audio stage	Recap; clean and repair the corroded area
Random crashes, RAM errors	Leaked electrolyte on RAM control lines, or bad DRAM/RAM card	Recap and clean; run the memory test; reseat ZIP DRAM / RAM card; check DRAM links
No display, machine boots	Monitor/cable, or VIDC output	Check analogue RGB at the 15-pin VGA connector; run the video test
Hard disc not found	IDE cable, drive power, or dead drive	Reseat the 40-way cable; run the IDE/hard-disc test; replace the drive
Dead, no rails	PSU	Check plug fuse and fan; exchange the PSU
Cuts out when warm	PSU fan/thermal shutdown	Clear the fan aperture; check the fan; exchange if persistent

Expansion

The A5000 has a four-slot podule backplane. If the machine misbehaves only with a card fitted, clean the backplane connector and the podule fingers and re-test; a shorted card or a dirty backplane connector is the usual cause. The Service Manual's procedure is to remove the backplane, retest, then refit and add cards one at a time.^[1]

Common fault catalogue

Completely dead — blown plug fuse or faulty PSU; check the fuse, then exchange the PSU.
Cuts out when warm — PSU fan or blocked aperture; thermal shutdown.
Intermittent / progressive odd faults — leaked surface-mount electrolytics; recap and clean (the single most common A5000 cause).
Lost time/config, corrosion by the FPA socket — leaked battery pack.
Disc corruption — RISC OS 3.00 ADFSBuffers bug; set ADFSBuffers 0 or upgrade.
RAM errors / crashes — leaked electrolyte on control lines, unseated ZIP DRAM, wrong DRAM links, or a bad RAM card.
No hard disc — IDE cable/power or a dead drive.
No video — monitor/cable or VIDC; run the video test.
Expansion only fails with a card — dirty backplane/podule contacts or a shorted card.

Related pages

Acorn Archimedes A5000
Acorn A5000 Maintenance Guide
Acorn A5000 Capacitor Guide
Acorn A5000 Service Manual · Acorn A5000 Circuit Diagrams
Acorn Archimedes A3000 Troubleshooting Guide — bus-level ARM/MEMC/VIDC/IOC checks
Capacitor Failure Symptoms

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 ^1.7 ^1.8 Acorn A5000 Service Manual (Module Level Service Manual, Issue 1, November 1991), Acorn Computers — hosted on this wiki. Source for the dead-computer procedure, the PSU rails (+5 V main PCB/floppy/HD, −5 V backplane, +12 V video SK1 pin 12), the 5 A mains fuse, the DRAM-size links, the ZIP DRAM, the A5000 functional test suite (test disc 0292,824) and the safety tests.

[sm-1] 1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 ^1.7 ^1.8 Acorn A5000 Service Manual (Module Level Service Manual, Issue 1, November 1991), Acorn Computers — hosted on this wiki. Source for the dead-computer procedure, the PSU rails (+5 V main PCB/floppy/HD, −5 V backplane, +12 V video SK1 pin 12), the 5 A mains fuse, the DRAM-size links, the ZIP DRAM, the A5000 functional test suite (test disc 0292,824) and the safety tests.

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