Dear, you must first verify the components next to the pwm, after discarding I recommend removing the pwm and if it does not turn on the flashing red light it is because the pwm is short-circuited, but before discarding you must measure the zener diodes, SMD transistors and surrounding components.
Thank you very much for your comment friend. I consult it if it is not annoyance: do you have or know where I can get the schematic of this tv box? I am having a hard time seeing where the pwd is, I send him a photo. greetings