OK. Since the voltages are different on all three, at least we know they are not shorted
to each other. And not to gnd or 5V. So maybe try changing the mux chip. If there is space,
it's always best to use a socket for the new chip, in case it ever needs changing again.
The traces on these old pcb's cannot handle too much rework without lifting or tearing.
I prefer the "good" kind of IC socket (machined pin). Although it makes getting the chip in and
out a little harder, I think it will be more reliable over time and the cost is not that significant
compared to your time.
to each other. And not to gnd or 5V. So maybe try changing the mux chip. If there is space,
it's always best to use a socket for the new chip, in case it ever needs changing again.
The traces on these old pcb's cannot handle too much rework without lifting or tearing.
I prefer the "good" kind of IC socket (machined pin). Although it makes getting the chip in and
out a little harder, I think it will be more reliable over time and the cost is not that significant
compared to your time.