Id be replacing both C407 & C224.. these are the caps on input/output but there is another cap tied to the chip itself that takes away ripple noise.. id be replacing that also.
If you look at U204 in your pic, directly below is cap C272.. this is the noise ripple cap for that chip and will be tied to the earth on the chip.
You have a chip for switch rows and a chip for switch column.. we don't know which is the one we want so replace the filter caps on both of these.... so 4 caps all up to be replaced, this will completely cover you.
Just to add that the caps are Tantalum.. these quite often fail and can be replaced with a simple ceramic 0.01Uf or whatever the value was
