IBM System x3650 M3 4255 Service Manual page 81

A checkpoint code is either a byte or a word value produced by server firmware
and sent to the I/O port indicating the point at which the system stopped during
the boot block and power-on self test (POST). It does not provide error codes or
suggest replacement components. These codes can be used by IBM service
and support for more in-depth troubleshooting.
Note any LEDs that are lit, and then push the light path diagnostics panel back
into the server.
Notes:
a. Do not run the server for an extended period of time while the light path
diagnostics panel is pulled out of the server.
b. Light path diagnostics LEDs remain lit only while the server is connected to
power.
Look at the system service label on the top of the server, which gives an
overview of internal components that correspond to the LEDs on the light path
diagnostics panel. This information and the information in "Light path diagnostics
LEDs" on page 65 can often provide enough information to diagnose the error.
3. Remove the server cover and look inside the server for lit LEDs. A lit LED on or
beside a component identifies the component that is causing the error.
The following illustration shows the LEDs on the system board.
Checkpoint
code display
63
Chapter 3. Diagnostics