Light path diagnostics is a system of LEDs on the front panel and on various internal components of the compute node. When an error occurs, LEDs can be lit throughout the compute node and the PCIe Expansion Node to help identify the source of the error.
Internal light path diagnostics for the PCIe Expansion Node can be initiated using two methods. The primary method is the power button on the associated compute node. When the compute node power button is pressed, the light path LEDs in the compute node and in the PCIe Expansion Node illuminate. The alternate method is a push-button switch located on the PCIe Expansion Node system board. The PCIe Expansion Node light path diagnostics button illuminates the light path LEDs if the compute node cannot due to a failure in the compute node or in the interposer cable.
When the PCIe Expansion Node is not installed in the system, a capacitor on the system board is used to energize the light path system. The capacitor circuit can keep all internal light path LEDs illuminated for minimum of 20 seconds of continuous operation.
See the Installation and Service Guide for the compute node for more information about using light path diagnostics to troubleshoot the compute node.