Solution: After replacing Q901 and ZD901 with the same model, everything returned to normal. Source: http://blog.163.com/samsung_dianshi88/. Samsung TV, no raster, no image, no sound.
Theoretical analysis and actual measurement: The power-on circuit of this TV is composed of D901 and R902, mainly providing bias for IC901 to start the switch-mode power supply. After startup, the induced voltage from pin 5 of T901 is stabilized and filtered through D903, Q901, and ZD901, providing bias voltage for the internal switching transistor's base at pin 9 of IC901. After oscillation, the voltage induced by the secondary winding of T901 is rectified by D906, D911, and D909, respectively providing 145V, 30V, and 18V voltages. Voltages of 8V and 5V are provided through D910, IC904, D908, and IC903. Therefore, the key components to check are the power-on circuit (D901, R902) and the feedback bias circuit (D903, Q901, ZD901). Upon inspection, it was found that Q901 and ZD901 were damaged (short-circuited).