Just look for 24Vdc from the actual fuses to common. Common is any metal piece on the machine, cabinet backplane, a2100 metal enclosure, door hinge, etc. Dont worry about my pcb trace comment; it was not meant as something you should check, just to alert you that IF you DO have 24vdc on the fuse, then the problem may be inwards on the io board. Like you say, it is more likely you are missing the 24v at the fuse so easier to trace back to where it is missing from. Good luck.