Service manual

Service Manual
Appendix D - Earth continuity testing
Equipment required
An earth continuity tester capable of sourcing 25A
derived from an AC source with a no-load voltage not
exceeding 12V.
It is recommended that the calibration and operation of
the instrument be checked frequently enough to ensure
its accuracy.
Test Procedure
The test should be performed on a fully assembled
computer.
Using the earth continuity tester, check the continuity
between the power supply cord plug earth/ground pin and
the following points:-
1 the rear panel internal expansion card fixing screws
2 fixing bolts for
• printer/parallel port (D-type)
• Analogue RGB port (D-type)
• any other expansion cards (eg SCSI).
The resistance measured between the earth pin and each
of the above test points shall not exceed 0.15 CI This
value includes an allowance for the resistance of the
mains cable. The duration of each test shall not exceed
10 seconds. No waiting period between tests is
necessary.
DANGER
THE FOLLOWING TESTS INVOLVE HIGH
CURRENTS BUT LOW VOLTAGES. ALL
NECESSARY PRECAUTIONS MUST BE TAKEN TO
ENSURE OPERATOR SAFETY DURING TESTING.
DANGER
SWITCH OFF THE COMPUTER, DISCONNECT IT
FROM THE MAINS SUPPLY, AND DISCONNECT
ANY PERIPHERALS BEFORE CARRYING OUT THIS
TEST.
Earth continuity test points
WARNING
YOU MUST NOT ALLOW THE
TEST PROBE TO TOUCH
ANY OF THE CONNECTORS'
SIGNAL PINS AS THIS WILL
DAMAGE THE EQUIPMENT.
Appendix D - Earth continuity testing Issue 2, June 1991 D-1