Check whether the output is normal, if normal, it indicates that the protection circuit misoperates; Touch the switch tube is hot? It should not be hot when unloaded, otherwise the output may have problems such as short circuit
Along the line is to fine-tune the 1k adjustable resistor, short-circuit the output voltage of the adjustable resistor to 14V, change the adjustable resistor to adjust the output voltage to 12V to restore the normal state. The voltage of pin 12 is 16V.
Check the resistance value of the upper and lower bias resistance of the voltage adjustment potentiometer and the resistance value of the potentiometer itself