Look at the silk-screen labels (e.g., R101, C202). If a component is charred, search for the part numbers of the components immediately surrounding it to infer the missing value.
Often centered around a PWM (Pulse Width Modulation) controller that regulates the output voltage. bm5291 ver 13 schematic free
Version 1.3 often includes upgraded Zener diodes and thermal fuses to prevent overcurrent damage. Troubleshooting Without a Schematic Look at the silk-screen labels (e