Since entire columns of keys don't work, it might just be one diode or solder pad that is causing the problem. If you inspect each solder pad (the metal ring around the hole where the pin comes through) you might be able to find which one got damaged or lifted. Same does for diodes, test each one to make sure they are all working. If that doesn't turn up the source of the problem, you could try what I did: test for continuity between each switch and its diode. The diodes should be marked with a D followed by the number that corresponds to the key position (usually starting with a K, probably on the other side of the PCB). Try each end of the diode with each pin of the switch until your multimeter reports continuity. Then do this for each switch/diode until you find where the break is. PCBs can be complex. When I had a lifted solder pad, I ended up having to make a bridge a few keys away to fix it.