Dear all help needed ,I have a problem Megadyne Mega Power ESU error 221 .The manual says VSV Error Voltage sense error at Power on Self test (POST).The fault is definitely on the main PCB I swapped it out.Can anyone maybe help with where the fault may lie as this is a common problem on many of my units,Im trying to trace the culprit or culprits.There is a multiturn pot on the PCB ,does anyone have calibration procedures ,none in my manual and no actual on board test point values in the manual ?Thanks. Show less