I would use a meter to check continuity from the keyboard connector to U24 and U25 (4051) (page 6 of the schematic). Then I would check from U24,U25 to POKEY. If you check continuity from the top of the board, with the chips plugged in, by touching the top of the IC leg, this will make sure that there's no break in the trace from a bad via or anything. Possibly U24, U25 is bad? Do other POKEY functions work, like the pot inputs, sound, etc?
Ouch, ouch, ouch. The XE boards are terrible for traces lifting with too much soldering iron heat. Did the through plating survive? Perhaps in the process of removing the socket, you tore out a through hole plate, thereby disconnecting a top trace from a bottom trace?