The frustrating service calls for us were the intermittent shutdowns. Pivots would run for two hours or twenty then stop just because. The farmers would naturally try to restart them which would hide clues to the problem. Things would work fine for us sometimes even if the farmer didn't mess with them. Our ohm/voltage meters would tell us what we could see with our eyes. A-OK, good to go. Sometimes the problem was with the power units which really weren't our focus. A couple I remember would overheat on a really hot day. It came down to repeated trips and just being more stubborn than the problem. A picture here of an irrigation power unit if anyone is interested:
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