Mitsubishi Electric MELSEC Q Series Reference Manual page 128

(3) Precautions
When the QJ71GP21(S)-SX fails, loopback may not be performed depending on what kind of failure occurs.
In such a case, data link may be stopped. To identify the QJ71GP21(S)-SX with a failure, perform either of the
following.
• Identify a faulty station by checking the LED indications (off of RUN LED, on or flashing of ERR LED) of all
QJ71GP21(S)-SXs.
• Power off all stations, then power on stations in order, starting from the control station. While doing this,
check that which station on the network loopback is performed normally. Check whether the control station
and a reconnected normal station are displayed on a loopback station in the network information display of
the CC-Link IE Control diagnostics.
Replace the QJ71GP21(S)-SX where a failure was detected with a new one and check that data link has returned
to normal status.
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