Diagram SOlution

What do you think of building a simple LED tester, so you can test the integrity of the components before soldering directly to the PCB. It reduces the task of testing the meter components using the circuit with LED gives an indication about the good or bad condition of the component.

When a component is placed in the circuit and establishes electrical continuity T1 receives base current through R1. When T1 conducts, the green LED turns on and off the red LED. This indicates that the component to be tested is good. If the component is bad, will not have electrical continuity and T1 remains off. In this state only the red LED light indicating that the component is bad.
 

  Polarity

Connect the red end of the positive range to the circuit board and to test the black edge point. Circuit board under test to be lit
Green LED ON - positive feed. Green LED off and red LED - or no negative supply voltage.
 

Continuity

Connect both ends red and black throughout the test points
Green LED-Continuity. LED red if there is no continuity
Resistor. 1 ohm to 500K

Alloy ends red and black on each side of resistor
Green LED Resistor-OK. Green LED off and red LED Resistor burned
 

Electrolytic capacitor

Red probe tip to positive and black for negative capacitor.
Green LED turns on and off gradually and then red lights, Capacitor good. Red LED lights up steadily bad capacitor

LED diodes, photodiodes, infrared diodes

The Red pontaa probe anode and cathode Black
Green LED - LED Good and Green LED off and red LED diode, or LED bad
Change the direction of the tips. If the green LED diode or LED is open


LDR

Tips in red and black leads of the LDR
Under the light, green LED and red LED fading. covering the LDR with your hand. Green LED off LDR good