We've got hundreds of hours of experience on these. We've drawn schematics of the DC-AC module and the drive circuits on the mainboard. We've developed a method of repairing them that includes checking all of the drive circuits and signals. We then connect the module so we can monitor it as we increase the input voltage from a current limited outside source. Once we have it running at the designated DC input voltage (215VDC) we monitor the waveform to ensure a clean stable sine wave output.