Maintenance points:
(1) If the B+ voltage has no output, check whether the external overcurrent detection component of the 2 pin is overcurrent, and check whether the 4 or 1 pin power supply is Normal, if necessary, try to repair a 10kΩ resistor in parallel with TLP621 3 and 4 feet.

(2) If the B+ voltage is too high, mainly check the voltage regulator circuit components such as R952 ~ R955, Q928, IC902; B+ voltage is low, Then disconnect the Q924 collector, measure the B+ voltage, see if the fault is in the regulator circuit components or in the R928, D910, C917, D909 and other delay circuit components; B+ with poor load capacity, mainly check R911 ~ R913, IC901, T901, Q901, D906, D924 and other components.