Service manual

Troubleshooting 3-3
CPU LEDs
• If the CPU STP LED on any CPU module is lit, that CPU chip is functioning
properly. If the operating system is NT and the CPU STP LED is off, that CPU
may or may not be functioning.
You can use the Halt button on the OCP to prevent the AlphaBIOS console
(which turns off the CPU STP LED) from booting, thus assuring the validity of
the CPU STP LED. If the LED is off, replace the CPU. If the LED is lit, you
can use the SRM console command alphabios to load and run the AlphaBIOS
console.
• The top LED on a CPU module is a DC OK LED. It is driven by the PCM
module. If it is not lit, there are probably power problems.
• The second from the top LED on a CPU lights only when the SROM on the
CPU is loaded.
• On modules with EV56 CPU processors a fourth LED is present at the bottom of
the column. The LED is normally on indicating that the power regulator on the
module is working properly. If the LED is off, replace the module.
System Bus to PCI Bus Bridge Module LEDs (B3040-AA)
There are four LEDs on the B3040-AA system bus to PCI bus bridge module:
• The top two LEDs indicate the condition of the bridge module. If either is off,
the module should be replaced.
• The bottom two LEDs are passed from the PCM. Both should be on during
normal operation. If either is off while the system is on, the LEDs on the PCM
module should indicate what failed. If they do not, the PCM could be broken or
the bridge module is not passing the signals to the LEDs.
NOTE: If AC power is applied and the system is off and a power supply is in
operation, the power LED, the top one of the bottom two, flashes, indicating the
presence of Vaux (auxiliary voltage).
System Bus to PCI Bus Bridge Module LEDs (B3040-AB)
There are two LEDs on the B3040-AB system bus to PCI bus bridge module:
• The two LEDs indicate the condition of the bridge module. If either is off, the
module should be replaced.