Turn the power off and remove all power cord connections to all components, including the connections to the systemboard, and all power cords to drives.

Turn the power back on. If the fan comes on, the problem is with one of the systems you disconnected, not with the power supply or its fan. Turn the power off and reconnect the power cords to the drives. If the fan comes on, you can eliminate the drives as the problem. If the fan does not come on, try one drive after another until you identify the drive with the short.

If the drives are not the problem, suspect the systemboard subsystem. With the power off, reconnect all power cords to the drives. Turn the power off and remove the power to the systemboard by disconnecting P8 and P9 or P1. Turn the power back on.

If the fan comes back on, the problem is probably not the power supply, but a short in one of the components powered by the power cords to the systemboard. The power to the systemboard also powers interface cards. Remove all interface cards and reconnect plugs to the systemboard. If the fan still works, the problem is with one of the interface cards. If the fan does not work, the problem is with the systemboard or something still connected

to it. A short through the systemboard might be caused by allowing the connections on the bottom of the systemboard to accidentally make improper contact with the chassis, which can cause serious damage to the systemboard. Check for missing standoffs, the problem that most often causes these improper connections.  

Shorts in the circuits on the systemboard might also cause the problem. Look for damage on the bottom side of the systemboard. These circuits are coated with plastic, and quite often damage is difficult to spot.

Frayed wires on cable connections can also cause shorts. Disconnect hard drive cables connected directly to the systemboard. Power up with P8 and P9 or P1 connected, but all cables disconnected from the systemboard. If the fan comes on, the problem is with one of the systems you disconnected. Never replace a damaged systemboard with a good one without first testing the power supply. You don’t want to subject another good board to possible damage.

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