Re: Possible water damage
Your photograph has labels on the pcb telling what a key does (ctrl, alt, cap, tab, z, a, q, etc.). It's not clear what is the mechanism that makes contact. Is it a switch, or magnetic sensor, or a conductive pad touching copper or graphite traces?
Did you see whether liquid got into the faulty keys individually, causing corrosion/ shorting/ loss of contact, etc.)?
Or there is the possibility that a copper trace went bad (shorted, disconnected, etc.) affecting several keys. The keyboard is read via a grid arrangement of wires. Knocking out one wire causes a misread of all keys which depend on that wire. So if a single thin trace goes open or shorts, then that could cause a misread of many keys.
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At LD25 there is some discoloration. Nearby traces appear extremely thin and close together. Just a bit of corrosion could create a hairline break.
See if you can determine whether a trace has a hairline break.
It's best not to apply more than a couple volts from an ohmmeter or power supply, and even then it should be through a high-ohm series resistance.
If you can find suitable test points to measure voltage changes, and press the keys, then you may discover a pattern of behavior about keypresses and voltages on the pcb. This could be tedious. It would be easier if you could compare it with a good keyboard. But to troubleshoot your keyboard you need to find what makes the difference between working keys and faulty keys.