After examination boost capacitor, voltage diode, magnetron were normal. First remove the power transformer primary, secondary coil lugs, using the "buzzing" sound when Supplying AC 220V voltage across the primary access to power transformers, power transformers clamp meter used to measure load current of 6A is too large (normal is 3A), is a high-voltage transformer winding inter-turn short circuit. After replacing the power transformer, the whole back to normal.uSMservice manual download site