Dusting off an N90s

Just picked up a used N90s, dusted it off, and mounted my trusty 50 1.8 D. Weird thing: I can adjust aperture with the dial just fine in P mode, but when I switch A it goes to f22 and stays there. I can unlock the aperture ring on the lens and work it that way, but no dice when I lock it back up. So it works as expected in P, not in A...Any ideas? Thanks.
 
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