Light Path Diagnostics Cards
Light path diagnostics is a system of LEDs on various external and internal components of the server that leads you to the failed component. When an error occurs, LEDs are lit on the operator information panel on the front of the server, then on the failed component. By viewing the LEDs in a particular order, you can often identify the source of the error.
When LEDs are lit to indicate an error, they remain lit when the server is turned off, provided that the server is still connected to power and the power supply is operating correctly.