Troubleshooting Power Problems

A dead system that gives no signs of life when turned on can be caused by the following:

• Defects in AC power to the system

• Power supply failure or misconfiguration

• Temporary short circuits in internal or external components

• Power supply or other component failure

With four suspects , it's time to play detective. Use the procedure outlined next to find the actual cause of a dead system. If one of the test procedures in the following list corrects the problem, the item that was changed is the cause of the problem. Power supplies have a built-in safety feature that shuts down the unit immediately in case of short circuit. The following steps are designed to determine whether the power problem is caused by a short circuit or another problem:

1. Check the AC power to the system; a loose or disconnected power cord, a disconnected surge protector, or a surge protector that has been turned off will prevent a system from receiving power.

2. Check the AC voltage switch on the power supply; it should be set to 115V for North America. Turn off the power, reset the switch, and restart the system if the switch was set to 230V.

3. Check the keyboard connector; a loose keyboard connector could cause a short circuit.

4. Open the system and check for loose screws or other components such as loose slot covers, modem speakers , or other metal items that can cause a short circuit. Correct them and retest.

5. With ATX/SFX power supplies, verify that the cable from the front-mounted power switch is properly connected to the motherboard.

6. Check for fuses on the motherboard ( mainly found in very old systems). Turn off the power, replace any blown fuse on the motherboard with a fuse of the correct rating, and retest.

7. Remove all expansion cards and disconnect power to all drives ; restart the system and use a multimeter to test power to the motherboard and expansion slots per Table 5.2, earlier in this chapter.

8. If the power tests within accepted limits with all peripherals disconnected, reinstall one card at a time and check the power. If the power tests within accepted limits, reattach one drive at a time and check the power.

9. If a defective card or drive has a dead short, reattaching the defective card or drive should stop the system immediately upon power-up . Replace the card or drive and retest.

10. Test the Power Good line at the power supply motherboard connector with a multimeter.

It's a long list, but chances are you'll track down the offending component before you reach the end of it.