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Power Check
WARNING:
There is a risk of electrical shock, the power supply unit can deliver an electrical shock even when
mains power is removed from the unit; be certain to observe all standard safety precautions.
TOOLS:
Digital Multimeter
PROCEDURE:
This procedure checks that there is power reaching the motherboard at the correct voltage. It does
involve testing the PSU whilst the power is applied, do not under any circumstances touch the
power supply or any high voltage component with anything other than protected probes of the
multimeter.
1.
The unit should be powered up with a mains cable that has been previously known to work.
Ideally the cable and plug fuse (country dependant) should be checked with a multimeter. Make
sure that the power cable is plugged into the unit and wall socket and the socket is switched on.
2.
Check that the mains IDC inlet filter is correctly plugged into the PSU. You will need to remove
the PSU protective cover to gain access, which should have been fitted before attempting the
repair. There are two connectors from the inlet filter, one for the earth and the other for deliver-
ing live and neutral. They are fitted to the PSU towards the rear of the unit.
Use the multimeter to ensure that there is current reaching the live wire (Alternate Current). If
no current is present then remove the power cord and check both the fuse on the PSU and in
the mains IDC inlet filter fuse holder. The fuse holder can be found just below the power cord
socket which can be prised open with a flat bladed screw driver.
3.
The motherboard and PSU are connected together with a short six wire cable, Ensure that the
cable and connectors are fitted securely. The voltage from each connectors pins must be
tested using a multimeter to ensure they match the following values :-
Blue:
-12v
Black (x2):
Ground
Red (x2):
5v
Yellow:
12v
Please Note: Whilst checking the pins the voltage may fluctuate with the ever changing load
on the system. However if any of the pins should seriously deviate from quoted figures then
this could indicate a problem with the PSU.
4.
Fit the PSU protective cover if removed at any point during this procedure.
PSU FINAL DIAGNOSIS:
1.
The PSU is fully operational if the following is true:-
•
The correct voltages quoted in this procedure are being output to the motherboard.
2.
It should be replaced only if the following is true :-
•
Cables and fuses have been fully tested with a multimeter.
•
There is either no output, no output on one or more pins or there is serious deviations in
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