Technical data

4-72 Fault Isolation

C. Switch the system unit power off and remove the power supply screws and

slide the power supply out about 3 inches. Switch the power on and mea

sure the voltages on the two power supply connectors as shown in

Figure 4-22 and Figure 4-23 (leave the connectors connected to the power

supply and measure the voltages through the rear of the connectors). If the

voltages are not present, go to Step D. If the voltages are present, go to

Step E.

D. Check Pin 24 on the large connector shown in Figure 4-22 for + 5 V dc. If

the voltage is not correct, replace the power supply.

If the voltage is correct at Pin 24, close the power-on switch. If you read

Pin 24 at ground, replace the power supply. If you still detect + 5 volts,

replace the power-on switch. If the new switch doesn’t ﬁx the problem, go

to Step E.

E. Either the power distribution cable, motherboard, or CPU board are defec

tive. Check the power distribution cable for continuity. If the power distri

bution cable is defective, replace it. Otherwise, replace the CPU board and

recheck the voltage test points. If the voltages are not present, replace the

motherboard.

5. If the voltages are present at the CPU board or power supply test points but not

within tolerance, perform the following steps

A. Power off the system unit and unplug the ac power cord from the power

supply. Replace the power supply.

B. If the problem persists, reinstall the original power supply and follow the

information in this step to check for power loading by a board. Power off

the system unit and remove one board other than the CPU board. Power

on the system unit and retest. If necessary, repeat this procedure for a sec-

ond board. If you replace a defective board, conﬁgure any switches or

jumpers the same as the original board.

C. If a board does not appear to have caused the problem, power off the sys-

tem unit and unplug the power cord from the power supply. Reinstall the

boards in their slots.

D. Unplug the internal mass storage power distribution cable from one of the

mass storage devices. Power on the system unit and recheck the voltages.

If necessary, repeat this step for each internal mass storage device. Re-

place the mass storage device if the voltages are within speciﬁcations.

end of procedure