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the keyboard is out, so that's my first place to start
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About that: You mentioned that some keys do work, and by that I trust you mean that when you press one of those keys the correct character appears. When you press the other keys, nothing happens?
If you want to check the keyboard scanning hardware independently of the keyboard itself you can unplug the keyboard and 'type' characters by joining keyboard row and column pins together with a jumper lead. We can probably find more detail on this if you need it, because in John Earland's original PET thread his original problem was a fault on the key scanning hardware (not the keyboard) so we accumulated quite a bit of info about the keyboard connector in that thread.
Also, in the Daver2 test screen you've just posted do you see that line 'Kbd' followed by a row of 00s? I think when you press keys those numbers should change.
I would say that the keyboard is the next essential repair because once that's working you can write small BASIC programs to test other aspects of the machine such as the IEEE interface, which can be tested using a few PEEKs and POKEs from BASIC.