Has anyone figured out what goes bad in these servo amps? I have about 5 or 6 I'd like to fix for spares but I don't want to send them out for repair because I think it's something simple I can't see anything burnt on the boards and I've tested everything I can test on them and can't find the problem which makes me think it's 1 of the 4 things mounted on the back but Idk for sure