Light path diagnostics on Power Systems

Light path diagnostics is a simplified approach for repair actions on Power Systems™ hardware that provides fault indicators to identify parts that need to be replaced.

Light path diagnostics is a system of light-emitting diodes (LEDs) on the control panel and on various internal components of the Power Systems hardware. When an error occurs, LEDs are lit throughout the system to help identify the source of the error.

With light path diagnostics, the fault LED for the FRUs to be replaced will be active when the unit is powered on. The failing FRUs can be attached to another FRU, which must be first removed to access the failing FRUs. For those cases, light path diagnostics provides a blue switch on the FRU that has to be removed first. When the first FRU is removed, you can press and hold the light path diagnostics switch to light the LEDs and locate the failing part. In most of the situations, the switch will have enough power stored to activate the LEDs for two hours after the unit has been powered off. However, this can vary significantly and therefore the switch should be used as soon as possible. The amber LEDs can normally be kept active for 30 seconds, however, this can also vary. Associated with the light path diagnostics switch is a green LED that will be activated when the switch is used and there is enough power stored to activate the amber LEDs. If the green LED does not activate when the switch is pressed then there is not enough power remaining to activate any amber LEDs on that FRU. If that happens then light path diagnostics and FRU identify function cannot be used for replacing the failing FRUs. Perform the repair action using the location codes in the error log or if determined by problem analysis as if the unit did not have light path diagnostics and did not have functioning identify LEDs.

At the core of light path diagnostics is a set of fault indicators that are implemented as amber LEDs. These LEDs provide a way for the diagnostics to identify which field-replaceable unit (FRU) needs to be replaced. Service labels, color-coded touch points for the FRUs, and a no tools required design for FRU removal and installation are all elements of light path diagnostics.

With light path diagnostics, at the same time that the diagnostics create an error log for the problem, it also activates the fault indicator when a FRU has a failed or failing component. This includes predictive failure analysis (PFA). The FRU fault LED is turned on solid (not flashing). Whenever a fault indicator is activated the enclosure's external Fault indicator on the operator panel is also turned on solid. The enclosure fault indicator on the panel means that inside the unit one or more FRU fault indicators is on. The error log shows the part number and location code of the FRU that must be replaced along with other FRUs or procedures to follow if replacing the first FRU does not resolve the problem.

If the diagnostics determine that the problem is firmware related, configuration related, or not isolated to a specific FRU then no fault indicator is activated. For these kinds of problems the amber System Info indicator on the operator panel is activated. The error log shows the procedures to follow and the possible FRUs that could be causing the problem.

During the repair action, the service label on the service access cover shows the FRUs and the steps required to remove or install the FRUs. Therefore, the basic flow of the repair is that the LEDs show which part to replace, the color-coded touch points indicate if the unit must be powered off to remove or install the part, and the service label shows the steps needed on the touch points. The FRU fault LED is not an indication that the FRU is ready to be replaced. To replace the FRU, some preparation steps might be necessary, such as removing the resource from use or powering off the unit. The service label and the touch point colors give the initial guidance for FRU removal.

When a FRU has been replaced, the fault indicator automatically turns off either when the new FRU is installed, or when the power is restored to the new FRU. This automatic shut off might take several seconds to a minute as the new FRU is powered on, brought online and tested by the system. When there are no more FRU fault indicators on in an enclosure then the enclosure's Fault indicator on the operator panel turns off automatically.

In addition to the fault indicators, there are also amber identify indicators for each FRU. The identify indicators flash when activated. Identify indicators are used to help a servicer identify where a location is. The location may be occupied or empty. The servicer can turn them on and off from a user interface either during a repair action or during the installation of new parts or when removing parts. The identify indicator visually confirms where a location code is. Whenever an identify indicator is activated, the enclosure's blue locate or beacon LED on the operator panel is also activated (flashing).

The same amber LED on a FRU can be used for both fault and identify indications. Whenever the LED is on solid for a fault, the LED switches to flashing when the FRU identify function is turned on. When identify function is turned off, the LED returns to fault (solid on) if that was the previous state of the LED.