[GreenKeys] Weird 33 keyboard problem

[Charles]

I'm having a weird problem with the keyboard on one of my 33s. In
short, some keys (but not all) don't output their shifted
character, just the non-shifted one. For example:

The SHIFT key works properly on numbers keys (but not the entire
top row, the - = won't shift).

base  1 2 3 4 5 6 7 8 9 0 : - 
shift ! " # $ % & ' ( )   * -

Note that the : * key works but not the - = key...

The P @ and the ; + keys do work properly.

And finally K L   N M    , . /  entirely refuse to shift to the
expected    [ \   ^ ]    < > ?

but just print the unshifted character.

I'm having trouble figuring out what contact wire(s) could be
causing some characters to shift but not others... any ideas?

thanks
Charles