AC 800M PM866 redundant controller fault light blinking
Be ensure the following while upgrading the firmware in the red controllers.
1.disconnect he RCU link cable from the CPU to which you are going to upgrade and connect the RCU link/ TB852 terminator.
2.remove the battery if any
3.remove the CN1/CN2 if you are using PPP for serial firmware upgrade.
4.open the firmware upgrade utility and press connect and press INIT button on the controller till R flashes for 3 times
then the upgrade the firmware.