Big shout out to #BeebleBrox over on #AtariAge for some kind and helpful advice on where to go next with my gorgeous #Atari #130XE with dead console keys.
Thanks to their guidance, I was able to identify my keyboard type and confidently open it up to examine the Mylar membrane. At first glance it looked pristine, but on closer visual inspection and doing continuity checks with a multimeter, I found a break - which someone else had thoughtfully highlighted for me!
I've ordered a new membrane from #Retrohax_de, which seems to be the same https://retronics.eu membrane as sold by https://retrolemon.co.uk.
(The membrane available from https://www.retrofuzion.com appears to be for the rubber dome version, comparing it with the other variant from retrolemon, though they don't say.)
I'd never have figured all this out without the kindness of strangers. Thank you, Beeblebrox. And the mystery person who had inspected this membrane before and highlighted the break!
https://forums.atariage.com/topic/142703-xe-xl-keyboard-troubles/#findComment-5650771