Hi Im work with UNITRONICS OPLC 4 years ago, with M90 and VISION 280, with out problems!. is a good equipment, easy to program ( with a lot of tools). If you ve already had to replace an I/O board and a complete unit. check the lnstalation and electrics proteccions. in order to if the OPLC was correct conected and installed, you dont have a futhers problems. CHECK : The instalations manuals. PD-: If you have any other cuestions, i can help you. i got lot of experience with this plc too PD: Sorry my english is not the best. Att: ALEXANDER GALINDO A agalindo@post.com