This is a typical protection circuit into the protection of the state of the phenomenon. First detection point A potential in the figure, 0 V low potential, it was ruled out of 10 V, 140 V line overvoltage and field have over-current failure, and test point B potential of about 0.1 V, C point potential of 2.2 V, confirmed the protection circuit has action. Measured D820 the positive potential of 0 v, that is not caused by a 300 v over-voltage protection. Cause of point B potential drop is only two: one is the short circuit between D8193, 4 feet, 2 it is Q856 c and e a very broken down. Removed the two components, inspection, found Q856 c and e very short circuit. After the replacement Q856 troubleshooting.iKwservice manual download site