If different coins are being rejected the coin comparator is working correctly and the problem is more likely to be the optic board under the comparator. My first guess is that the platic coin guide may be to big for the coins you are using.

This video will show you the trick to installing a coin into a coin comparator. One thing to remember, is that if there is no coin inside the comparitor, the machine will not work. And no matter what coin kind you have in the hopper, whether quarter, nick

Solution on vending coin mechanism not accepting coins. cut appropriate cardboard into the shape of the coin guide; shape and funnel it to the coin mechanism using scotch tape; I took a video on how to cut the cardboard and taped it on the metal funnel in