Editing Acorn A5000 Troubleshooting Guide

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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'''.<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 dead-computer procedure, the PSU rails (+5&nbsp;V main PCB/floppy/HD, &minus;5&nbsp;V backplane, +12&nbsp;V video SK1 pin&nbsp;12), the 5&nbsp;A mains fuse, the DRAM-size links, the ZIP DRAM, the A5000 functional test suite (test disc 0292,824) and the safety tests.</ref>

== ⚠️ Mains warning ==

The A5000 has a fan-cooled mains PSU. '''Its primary side and its reservoir and mains-suppression capacitors can hold a lethal charge even after the machine is unplugged &mdash; a shock can be fatal.''' Disconnect the mains lead before removing the cover, and never work on the supply while it is plugged in. The PSU can be opened and recapped as part of a restoration (Acorn's exchange-only advice predates the modules being unavailable), but only if you are competent with mains switch-mode supplies: discharge the reservoir capacitor and confirm 0&nbsp;V before touching the primary side (see the [[Acorn A5000 Capacitor Guide]]). Re-apply the earth-continuity and DC-insulation safety tests after any internal work.<ref name="sm" />

[[File:Acorn A5000 circuit diagram (1 of 4).png|center|thumb|680px|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:<ref name="sm" />

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

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{| class="wikitable styled-table" style="width:90%; text-align:center;"
|+'''A5000 supply rails'''
! Rail !! Feeds
|-
| +5&nbsp;V || Main PCB, floppy drive, hard disc
|-
| &minus;5&nbsp;V || Backplane expansion connector
|-
| +12&nbsp;V || Video connector SK1 pin&nbsp;12; floppy/hard-disc motors
|}

# If the PSU runs then cuts out, check the '''fan''' and that the fan aperture is not blocked &mdash; a stalled fan or blocked aperture causes thermal shutdown. Repeated shutdowns mean a faulty PSU.<ref name="sm" />

== Dead computer with power present ==

If the rails are good but the machine is dead, the Service Manual's checks are:<ref name="sm" />

* 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 &mdash; e.g. 4&nbsp;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 &mdash; 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 [[Acorn Archimedes A3000 Troubleshooting Guide|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 &mdash; 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.<ref name="sm" /> 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 &mdash; 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:<ref name="sm" />

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{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''A5000 functional tests and what they exercise'''
! Test !! Exercises
|-
| Memory test || the 2&nbsp;MB / 4&nbsp;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.<ref name="sm" />

== Specific faults ==

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{| class="wikitable styled-table" style="width:100%; text-align:left;"
! 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; recap the PSU (discharge first) or fit a known-good supply
|-
| 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.<ref name="sm" />

== Common fault catalogue ==

* '''Completely dead''' &mdash; blown plug fuse or faulty PSU; check the fuse, then recap the PSU (discharge first) or fit a known-good supply.
* '''Cuts out when warm''' &mdash; PSU fan or blocked aperture; thermal shutdown.
* '''Intermittent / progressive odd faults''' &mdash; leaked surface-mount electrolytics; recap and clean (the single most common A5000 cause).
* '''Lost time/config, corrosion by the FPA socket''' &mdash; leaked battery pack.
* '''Disc corruption''' &mdash; RISC OS 3.00 ADFSBuffers bug; set ADFSBuffers 0 or upgrade.
* '''RAM errors / crashes''' &mdash; leaked electrolyte on control lines, unseated ZIP DRAM, wrong DRAM links, or a bad RAM card.
* '''No hard disc''' &mdash; IDE cable/power or a dead drive.
* '''No video''' &mdash; monitor/cable or VIDC; run the video test.
* '''Expansion only fails with a card''' &mdash; 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]] &mdash; bus-level ARM/MEMC/VIDC/IOC checks
* [[Capacitor Failure Symptoms]]

== References ==

<references />

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[[Category:Acorn Computers]]
[[Category:Troubleshooting Guides]]