Hello , I just start having an issue with my MX4660, I have 3 push buttons connected to input 1, 2 and 3 fot cycle start, feed hold and stop cycle, +12v connected to OPTO1. They were working right but suddenly they are no longer working, I verified the volt between push buttons terminals (NO push buttons) they show 11.2v in normal state and drop to 2volt when I press the push butons. Any help where should i need to look for