Service manual

Part 1- Fault diagnosis and repair
Introduction
This chapter is a guide to the diagnosis and repair at a
modular level of basic faults in the Archimedes 5000
series computer system.
It consists of algorithms to enable you to trace and
remedy faults in a 'dead' computer, followed by
instructions for running the Archimedes functional test
software, which is designed to isolate faults in a computer
which is partly working.
Note: Throughout this chapter the acronym UUT is used
to mean Unit Under Test and the acronym CSW to mean
Central Service Workshop.
SAFETY CONSIDERATIONS
WHENEVER ANY SERVICE OR UPGRADE IS
PERFORMED, ENSURE THAT ALL THE FUNCTIONAL
TESTS AND SAFETY TESTS AS DESCRIBED IN THIS
SECTION ARE CARRIED OUT.
FULL FUNCTIONAL AND SAFETY TESTS SHOULD BE
APPLIED IRRESPECTIVE OF THE ORIGINAL FAULT OR
WORK PERFORMED.
FAILURE TO CARRY OUT THE TESTS IN FULL MAY
RESULT IN AN UNSTABLE OR UNRELIABLE UNIT BEING
RETURNED TO THE CUSTOMER.
DANGER
BEFORE ATTEMPTING TO OPEN THE COMPUTER
OR
EXCHANGE EITHER THE PSU (POWER SUPPLY
UNIT)
OR PCB, ENSURE THAT YOU HAVE READ AND
FULLY
UNDERSTOOD ALL THE INSTRUCTIONS IN Part 2 -
Disassembly and assembly. IN PARTICULAR, ENSURE
THAT YOU DISCONNECT THE COMPUTER, MONITOR
AND PERIPHERALS FROM THE POWER SUPPLY.
UNDER NO CIRCUMSTANCES SHOULD ANY ATTEMPT
BE MADE TO REPAIR OR MODIFY THE PSU. ANY
ATTEMPT TO DO SO WILL INVALIDATE THE ORIGINAL
SAFETY TESTS APPLIED AT MANUFACTURE AND MAY
CREATE A SAFETY HAZARD.
WHEN REFITTING OR FITTING A REPLACEMENT
ASSEMBLY, CHECKS SHOULD BE MADE FOR EARTH
CONTINUITY BETWEEN THE EARTH PIN OF THE MAINS
PLUG AND THE FOLLOWING:
• THE BASE METALWORK
• THE REAR PANELS (INCLUDING BLANKING PANELS
AND CONNECTING PLATE)
• THE TOP COVER
USE AN EARTH CONTINUITY TESTER SET TO 25 AMPS.
FOR DETAILS REFER TO Appendix C - Earth continuity
testing AND Appendix D - DC insulation testing - class 1.
Test equipment required
• DC Voltmeter
• A5000 test disc (Acorn part number 0292,824)
• a blank 1.6 MB ADFS F format write-enabled, 3.5
inch floppy disc (used as a scratch disc in the disc
interface test)
• test IDE hard disc (see the section entitled Creating a
test IDE hard disc on page 1-6)
• serial port loopback plug – see Appendix B - Serial
port loopback plug
• parallel to video loopback box (0092,800)
• headphones (32 ohm impedance)
• analogue multisync colour monitor (suitable for super
VGA)
• Epson FX80 compatible printer
• 2 x blank 800K ADFS E format write-enabled, 3.5
inch floppy discs:
• data disc– to store the customer's CMOS RAM
configuration data
• CMOS RAM test data disc– to store the
manufacturer's default CMOS RAM settings (see
the section entitled Creating a CMOS test data file
on page 1-7)
• working keyboard (0392,900) and mouse (0183,180)
• mouse test jig template (see Appendix A - Mouse test
jig template)
• working backplane (0192,004)
• standard hand tools, such as screwdrivers and pliers
• earth testers (see Appendix C - Earth continuity
testing)
• isolation tester (see Appendix D - DC insulation
testing - class 1).
Checking a 'dead' computer
This section describes the initial tests that you should
perform on an apparently 'dead' computer to discover
which module or upgrade is faulty. If the computer is
partially working (i.e. any faults occur after a successful
power-up) go straight to the section entitled Checking a
partly working computer on page 1-4.
To diagnose the faults in a 'dead' computer, refer to the
procedure given in the flowchart, Figure 1-1: Procedure
to check a 'dead' computer on page 1-2. The sections
following describe the actions to be taken when you
have isolated the fault on the computer.
Note: You may need to reconfigure the CMOS RAM to
its original (factory) default setting. Make sure that the
customer is made aware of this.
Part 1- Fault diagnosis and repair Issue 1, November 1991 1-1