Create continuity tester circuit with buzzer and LED for check solder joint defects, not kill components on PCB, as probe gives tiny current and voltage.
This is Simple Solar light alarm circuit with the special edition, that improve this circuit whole new to higher efficiency. use solar cell instead of LDR
See 3 ideas of 555 DC polarity probe tester circuit. Check Car Electrical in easy, find open circuit, automotive short circuit, loose connection. Learn more