This circuit is also use operational amplifier IC LM324 to drive the VN64GA with the error signal and to control output voltage. This output voltage is pulsating DC , which is quite satisfactory for battery charging. This circuit also can be converted to the system regulated DC supply. You do this by increased C2 and anoother electrolytic capacitor is added across the load. The respon time is very fast, determined by the op amp. Schematic and troubleshooting below : If the circuit not work , Perhaps the cause of : AC cable disconnected Transformer is damaged or leaking. Broken or leaky diode. Installation of inverted foot elco. Instrallation of the components of the upside , particularly on the transistor , examine the placement of the feet emitter , collector and base. IC damaged. Soldering is less sticky. Line PCB damaged.