You will get a high pitched sound when switches are pressed. Looks like the center coin mech input is stuck. Since it's not used or wired that would mean the input or output on the board is shorted to ground.
Check pin 13 of the ls244 @ R9 to see if it's high or low. Should be high.
Then check pin 7 same chip should be high as well.
If 13 is high, and 7 is low then the ls244 is most likely bad.
You can also check the pull up resistors R71 470 ohm for +5 and R65 1kohm for +5 maybe it's a cold solder joint.
You can always inject a +5v signal on pin 7 to see if it clears.