I reached out to Jesse and Kaya and got phenomenal reply. I am allowed to put that here, so hopefully it will be helpful for others too. For this second e-mail, I shall point out that this will void your waranty.
This is a tutorial I’d written for another user. He’d damaged an R2 key
rather than an R1 key, but the process is about the same. Is this enough to
get you going
The next thing to make sure is that the “B” leg has good connectivity to
the “C” test point:
If that looks good, the next thing is to see if the “A” leg has good
connectivity to another key that it should:
If it does not, the solution is to solder a wire between these two switch
If, however, both of those are good, we’ve likely narrowed the problem down
to the connection between the keyswitch and the diode.
If your multimeter has a diode testing mode, we can verify this. The
instructions for how to use a multimeter to test diodes are here:
The two points you want to test as the two sides of the diode are marked
below. The cathode side of the diode is the side nearest the failed switch.
If the diode turns out to work ok, then we need to dig deeper. If you can’t
get a diode reading, then the problem is almost certainly with the
soldering around this pin:
The low-tech, but permanent solution for this is to solder a through-hole
1N4148 diode (which is a very, very common type of diode and should cost a
few cents) to these two test points:
The diodes look like this:
The black bar should be on the side nearest the failing switch.
If you want to test this all and don’t have a diode handy, you can solder a
wire from the “C” point on the switch to the column test point.