Using Blown Fuse Indicators to Troubleshoot the M40e Router

The router uses fuses from the Cooper Bussman brand GMT series for the FPCs, MCSs, PCGs, and SFMs. They are located in a fuse box on the rear of the midplane. When the fuse for a component blows, the component stops functioning even though it is installed correctly and the power supplies are still providing power to the router.

Figure 1 shows the location in the fuse box of the fuse for each component. The labels shown in the figure do not appear on the actual fuses (the clear cover on every fuse reads BUSS GMT-X), but a table on the surface of the midplane below the fuse box displays the same information.

Figure 1: Fuse Locations in the Fuse Box

When a fuse has blown but the power supplies are still delivering power to router, the yellow LED adjacent to the fuse lights. For vertically oriented fuses (in the groups labeled J241 through J244 in Figure 1), the LED is located below the fuse; for horizontally oriented fuses (in the group labeled J240), it is to the left of the fuse.

Note: The LEDs are each about 0.1in. (2 mm) square. They might be difficult to see when not lit.

A blown fuse can cause a component to fail even though it is correctly installed and the power supplies are functioning. Check for a blown fuse in the following circumstances:

• The LED that indicates normal operation for the component fails to light.
• The appropriate CLI show chassis environment command indicates that the component is installed but is not receiving power.