During a failed upgrade to 800xA version 188.8.131.52 we ended up with a redundant pair of PM891 controllers that were made non redundant by the controller online upgrade tool. We are in the process of back tracking to the previous version and have downgraded firmware in the primary controller but are not able to in the backup controller. Note that the issue was that we were unable to download the applications to the controller(s).
We tried using the serial firmware upgrade tool to downgrade the firmware in the backup controller hoping to make them redundant after that by using the online upgrade tool after the firmware was downgraded but attempts to downgrade the firmware were not successful as the PM891 is not part of the system.txt file. There does seem to be a serup89x.bin file but it is not listed in the folder but it has not been added to the system.txt file. Not sure it this is an oversight or if a PM891 is downgraded another way but looking for any information folks might have.