Solved! Thanks Don, I was able to move the unit to a maintenance pool, vacating its data to two other units, then power it down, pull the SD Card from the "good" controller and copied those files to a desktop folder.  I reinstalled the good controller and pulled the downlevel controller out.  I removed its SD card and overwrote the files with the files copied from the "good" controller.  I powered up the SAN with just the good controller installed and after that came up (forcing the "good" controller to be the active one I installed the second controller hot.  After some minutes this controller came up and now has the same firmware and all is happy.
I have a PS 6100 with two Type 11 controllers.  One of the controllers went to not being present.  I obtained a new controller and installed that with the SD card from the previous controller.  The new controller also showed as not present.  I out the old controller back in, using the SD card from the new controller and it does show as present but it has firmware v7.1.14 while the active controller has v9.1.9.  I cannot update the firmware to v9.1.9, getting an error that the controllers have different firmware.  Is there any way to get the v7.1.14 controller up to the same firmware as the active controller? The initial issue appears to be a problem with it's SD card, not a bad controller per se.
Bad SD Card on PS6100 - need to upgrade firmware on different SD card