Editing Acorn System 4 Troubleshooting Guide

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[[File:Acorn System 4.jpg|thumb|360x360px|Acorn System 4 double-height Eurocard rack.]]

This guide gives diagnosis for the '''[[Acorn System 4]]''' (1980), a 14-slot double-height Eurocard rack with two floppy drives. Diagnose by card as for the [[Acorn System 3 Troubleshooting Guide|System 3]], with attention to the larger backplane and the integral mains power supply.<ref name="cat">[[Acorn System Catalogue]] and [[Acorn System 1 Technical Manual]], Acorn Computers &mdash; hosted on this wiki. Source for the Eurocard set, the Intel 8271 floppy controller and the shared card detail.</ref>

== ⚠️ Mains warning ==

The cased System 4 has a mains PSU. Disconnect the mains lead before opening; the PSU primary side is at mains potential.

== First: power and backplane ==

# With the mains off, then on (lid open, take care), confirm the backplane rails (+5&nbsp;V and any &plusmn;12&nbsp;V) at an empty slot. A dead rail points to the PSU or the backplane power wiring.
# On a 14-slot rack, reduce to a minimum (CPU + RAM + VDU) and add cards back one at a time to isolate a faulty card or a shorted card pulling a rail down.

== Card-level diagnosis ==

Use the System 1/2/3 guides for the individual cards:

* '''CPU card''' &mdash; [[Acorn System 1 Troubleshooting Guide]] (1&nbsp;MHz clock, 6502, ROM, RAM).
* '''VDU / memory cards''' &mdash; [[Acorn System 2 Troubleshooting Guide]].
* '''Floppy subsystem''' &mdash; [[Acorn System 3 Troubleshooting Guide]] (Intel 8271, ribbon, drives, alignment).

== Econet file-server faults ==

A System 4 used as an Econet server depends on the Econet card and the network: check the Econet card seating, the clock/termination on the network, and the file-server ROM. A server that boots locally but is invisible on the network points to the Econet card or the cabling rather than the CPU.<ref name="cat" />

== Backplane ==

With many slots, a single shorted card or a dirty contact can take down the whole rack. Pull all cards and add them back; clean edge fingers and backplane sockets; inspect the backplane power-input joints for cracks.

== Common fault catalogue ==

* '''Dead, no rails''' &mdash; mains PSU or backplane power wiring.
* '''Dead, rails present''' &mdash; CPU card; apply the System 1 checks.
* '''A rail collapses with one card fitted''' &mdash; shorted card; isolate by substitution.
* '''No disc''' &mdash; FDC (8271), ribbon or drive.
* '''Not visible on Econet''' &mdash; Econet card or network cabling/termination.
* '''Intermittent when jostled''' &mdash; dirty edge connector or backplane joint.

== Related pages ==

* [[Acorn System 4]]
* [[Acorn System 4 Maintenance Guide]]
* [[Acorn System 4 Capacitor Replacement Guide]]
* [[Acorn System 3 Troubleshooting Guide]] · [[Acorn System 1 Troubleshooting Guide]]

== References ==

<references />

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