Editing Acorn System 2 Troubleshooting Guide

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[[File:Acorn System 2.jpg|thumb|360x360px|Acorn System 2 in a 19-inch Eurocard card frame.]]

This guide gives component-level diagnosis for the '''[[Acorn System 2]]''' (1980). Because the System 2 is a set of Eurocards on an 8-slot backplane, diagnosis is by card: isolate the faulty card, then probe it against its circuit diagram. The CPU and cassette cards are the [[Acorn System 1]] cards, so the [[Acorn System 1 Troubleshooting Guide]] applies to them directly.<ref name="cat">[[Acorn System Catalogue]] and [[Acorn System 1 Technical Manual]], Acorn Computers &mdash; hosted on this wiki. Source for the Eurocard set and the shared CPU/cassette/VDU/memory card detail.</ref>

== Method: isolate the card ==

A racked system is best diagnosed by reducing it to a minimum and adding cards back:

# Confirm the backplane rails (+5&nbsp;V, and any &plusmn;12&nbsp;V used by the VDU) at an empty slot.
# Run with only the CPU card and the memory/BASIC card; confirm the machine starts.
# Add the VDU card, then the cassette card, retesting after each.
# A fault that appears only when one card is fitted isolates to that card (or a dirty slot).

== No display ==

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{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Symptom !! Probable cause !! Action
|-
| No video at all || VDU card, its rails, or the monitor || Confirm +5&nbsp;V/&plusmn;12&nbsp;V at the VDU slot; reseat the MC6845 and SAA5050; try another monitor
|-
| Garbage / wrong characters || SAA5050 or video RAM on the VDU card || Reseat the SAA5050; check the VDU card's RAM
|-
| Dead machine, no activity || CPU card (clock/6502) or no rails || Apply the System 1 CPU-card checks; verify the backplane supply
|}

== Memory and BASIC ==

The memory card carries the RAM and the Acorn System BASIC ROM. Corrupt operation or crashes point to the RAM; failure to enter BASIC points to the BASIC ROM or its select. Reseat the card, then substitute RAM. Adding the optional second 4&nbsp;KB RAM or the floating-point ROM changes the memory map, so verify links are set per the card documentation.<ref name="cat" />

== CPU and cassette cards ==

These are the System 1 cards. Use the [[Acorn System 1 Troubleshooting Guide]]: verify the 1&nbsp;MHz clock and 6502, the monitor ROMs, the 2114 RAM, and the LM358 cassette read level. In the System 2 the keypad and LED are unused; the CPU card's keyboard interface drives the external keyboard instead.

== Backplane and connectors ==

* A machine that works only when a card is pressed or wiggled has a dirty/loose edge connector &mdash; clean the fingers and the backplane socket.
* Check the backplane for cracked solder at the connectors, especially around the power-input pins.

== Common fault catalogue ==

* '''Dead, no rails''' &mdash; power supply or backplane power wiring.
* '''Dead, rails present''' &mdash; CPU card (clock/6502/ROM); apply the System 1 checks.
* '''No display''' &mdash; VDU card, its rails, or the monitor; reseat MC6845/SAA5050.
* '''Crashes / corrupt''' &mdash; memory card RAM; reseat/substitute.
* '''Intermittent when jostled''' &mdash; dirty edge connector or backplane joint.

== Related pages ==

* [[Acorn System 2]]
* [[Acorn System 2 Maintenance Guide]]
* [[Acorn System 2 Capacitor Replacement Guide]]
* [[Acorn System 1 Troubleshooting Guide]] · [[Acorn System Catalogue]]

== References ==

<references />

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