since this is an 8920A may be more of a challenge since you need the calibrate routine and data ( usually fixed for the most part anyway) on an Epson type card.
Probably cheaper to just replace what you have .
I have a number of those low power input attenuators from upgrades as well if it is defective and there are plenty out there.
Just use an external high power attenuator and input the value in the settings screen ...will correct the input and output levels ...one of the nice things about the 892X.
Usually the low power option was pretty rare in an 8920A...mostly the standard 60W and the optional 100W out there.? 8920B's seemed to have a lot more variance in that regard.
