Fan showing high RPM values,
> show chassis fan
Item Status RPM Measurement
FPC 0 Fan Tray 0 Fan 1 OK 675000 Spinning at normal speed
Therefore caused below alarm,
> show chassis alarms
1 alarms currently active
Alarm time Class Description
Minor FPC0: Fan Tray 0 Fan 1 Spinning Upgraded
Fan came down to normal values by itself, however alarm may show up again,
https://prsearch.juniper.net/problemreport/PR1763499