Power problems can be difficult to solve. For example, a short circuit can exist anywhere on any of the power distribution buses. Usually, a short circuit will cause the power subsystem to shut down because of an overcurrent condition. To diagnose a power problem, use the following general procedure:

1. Turn off the HMC and disconnect all AC power cords.
   
   
2. For the 7042-CR4 HMC, check the power-fault LEDs on the system board and refer to the Service Guide for Deskside and Rack-mounted Consoles manual for information about the troubleshooting table describing power problems.
   
   
3. Check for loose cables in the power subsystem. Also check for short circuits; for example, if a loose screw is causing a short circuit on a circuit board.
   
   
4. Remove the adapters and disconnect the cables and power cords to all internal and external devices until the HMC is at the minimum configuration that is required for the HMC to start.
   
   The following minimum configuration is required for the 7042-CR4 HMC to start:
   
   
• One microprocessor in microprocessor socket 1
• Two 512 MB DIMMs on the system board
• One power supply
• Power backplane
• Power cord
• Five cooling fans.

The following minimum configuration is required for the 7042-C06 HMC to start:

• One microprocessor
• Two 512 MB DIMMs on the system board
• One power supply
• Power cord
• System board.

5. Reconnect all AC power cords and turn on the HMC. If the HMC starts successfully, replace the adapter and devices one at a time until the problem is isolated.
   
   If the HMC does not start from the minimum configuration, replace the components in the minimum configuration one at a time until the problem is isolated.