Editing Acorn System 5 Troubleshooting Guide

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[[File:Acorn System 5.jpg|thumb|360x360px|Acorn System 5 Eurocard rack with two floppy drives.]]

This guide gives diagnosis for the '''[[Acorn System 5]]''' (late 1982), a 10-slot Eurocard rack with two floppy drives and an integral mains power supply. Diagnose by card as for the [[Acorn System 4 Troubleshooting Guide|System 4]]; the [[Acorn System 5 Handbook]] gives the per-board detail.<ref name="hb">[[Acorn System 5 Handbook]] (1 March 1983), Acorn Computers &mdash; hosted on this wiki. Source for the standard card set (6502/6502A CPU, VDU, 32K DRAM, Intel 8271 floppy controller, Econet) and per-board information.</ref>

== ⚠️ Mains warning ==

The System 5 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 wiring.
# Reduce to a minimum (CPU + DRAM + VDU) and add cards back to isolate a faulty or shorting card.

== Card-level diagnosis ==

* '''CPU card''' (1&nbsp;MHz 6502 or 2&nbsp;MHz 6502A) &mdash; verify the clock and the 6502; on a 6502A board confirm the 2&nbsp;MHz timing. Apply the [[Acorn System 1 Troubleshooting Guide]] approach.
* '''VDU card''' (80×25 or 40×25) &mdash; check the video output and reseat the CRTC/character generator.
* '''32&nbsp;KB DRAM cards''' &mdash; DRAM faults give corruption or crashes; reseat the card and check its regulator (DRAM cards draw more current and stress the regulator). Confirm the memory-size links match the fitted DRAM.
* '''Floppy subsystem''' &mdash; Intel 8271 controller, ribbon and drives (see [[Acorn System 3 Troubleshooting Guide]]).
* '''Econet''' &mdash; check the Econet card and the network if the machine is a server.

== DRAM vs static RAM ==

Unlike the earlier static-RAM systems, the System 5 uses 32&nbsp;KB '''DRAM''' cards, which need correct refresh and timing. A DRAM card that fails the memory test or causes intermittent crashes should be reseated and its links checked before substitution.<ref name="hb" />

== Backplane ==

A shorted card or dirty contact can take down the rack; pull all cards and add them back, cleaning edge fingers and backplane sockets, and inspect the backplane power-input joints.

== Common fault catalogue ==

* '''Dead, no rails''' &mdash; mains PSU or backplane wiring.
* '''Dead, rails present''' &mdash; CPU card; apply the System 1 checks (confirm 1 vs 2&nbsp;MHz board).
* '''Corruption / crashes''' &mdash; a 32&nbsp;KB DRAM card; reseat, check links, substitute.
* '''No disc''' &mdash; FDC (8271), ribbon or drive.
* '''Not visible on Econet''' &mdash; Econet card or cabling/termination.
* '''Intermittent when jostled''' &mdash; dirty edge connector or backplane joint.

== Related pages ==

* [[Acorn System 5]]
* [[Acorn System 5 Maintenance Guide]]
* [[Acorn System 5 Capacitor Replacement Guide]]
* [[Acorn System 5 Handbook]] · [[Acorn System 4 Troubleshooting Guide]] · [[Acorn System 1 Troubleshooting Guide]]

== References ==

<references />

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