Who this guide is for If a machine stopped unexpectedly or behaves “on and off,” this article explains how professionals start testing —in plain language. You’ll learn what to check safely, what tools help, and what to send us  if you want a board-level evaluation. Safety first (please read) Disconnect mains and wait for DC bus capacitors to discharge. Use lockout/tagout where applicable. If you are not trained to work on live equipment, do not  energize it—collect the info l