There is no voltage in the 7th pin of the 3842 chip, there are generally three situations, one is the starting resistance is damaged, the second is the 3842 chip is damaged, and the third is no 300V voltage.
Start resistance damage is well judged, test resistance resistance value is normal. 3842 chip damage, 7 pin ground resistance is low or breakdown, chip can not vibrate. There is no 300V voltage on the power side, and there will be no voltage on the natural 7 pin.