I have an oscilloscope that has developed an arc in the high voltage power circuit and the only way I can do voltage checks without any sparks and damage to diodes is to use a Dim Bulb Tester with a 42 watt bulb in series with the 240v 50hz mains supply.The service manual for this oscilloscope says that V Line 1 is supposed to read between +209v and +231v,with the DBT I get +124v? V Line 2 is between +114v and +126v. I get +76v using the DBT? etc... Is there some way I can calculate the proper voltages from the readings I get on the DMM, as if the scope was plugged into the mains?