This is the simple Remote control tester circuit diagram. When the remote control is not working, first check the battery before, It may be loss.If it is good,so detect transmit infrared light device.However, because the human eye can not see infrared light,so can not know how good or bad.But the photo transistor can use to detect infrared light.
This circuit so use this photo transistor is the light receiver from the remote control.If it is nice to have the bias current of the transistor BC558.It runs a current flows through the LED,so the LED bright.The remote control that works correctly. The variable resistor VR1 is used to adjust the sensitivity of the circuit.
Remote control tester circuit diagram