Every electronic device contains one or more printed circuit boards, or PCBs. As technology is improving and component sizes are getting smaller, the complexity of these PCBs is increasing. A typical commercial PCB found in an electronic device has more than two layers, but only the top and bottom layers are visible and accessible for testing. The traces flowing through inside of the board can not be accessed for electrical testing. One can test a PCB using a multimeter.
- Skill level:
Things you need
- Digital multimeter with fine-tip test leads
Lay the PCB on a flat surface with the component side facing up.
Insert the red lead of the multimeter into the "V" socket and the black into the "COM" socket.
Turn the multimeter's knob to the continuity testing position. Generally this position is marked with several small parallel lines.
Turn the multimeter on and test it by touching its two leads together. If you do not hear a beep, you either did not set up the multimeter properly or it is malfunctioning. One or both of the multimeter leads could be broken from inside, too. Take the appropriate action to set the multimeter right before moving on to the next step.
Touch two traces on the PCB that you suspect of having a short with the two leads of the multimeter. The order of the leads does not matter. If you hear a continuous beep, there is a short. Beeping means that an electrical continuity has been established, which can only happen if there is a short.
Turn the multimeter knob to the DC voltage test point. The point will have a "V" mark with two straight parallel lines.
Find the voltage regulator on the board.
Connect the PCB to its power supply and turn it on if it has a switch.
Touch the red multimeter lead to the positive input terminal of the regulator and black lead to any ground point on the board. The multimeter should display the voltage going into the regulator. This is the supply voltage. Verify that the value displayed on the multimeter corresponds to the correct voltage before moving on to the next step. If this is not correct, there may be a connection problem between the power supply and the PCB or the power supply may not be working properly.
Touch the red multimeter lead to the positive output terminal of the regulator and the black lead to any ground point on the PCB. The multimeter display should show the regulator output. Most PCBs work on either +5 V or +12 V. In general, if you are getting a voltage output in this range, the regulator is working fine. A 0 V is definitely a sign that the regulator is malfunctioning and needs to be replaced.
Tips and warnings
- Never test a PCB that is connected directly to the AC line using this method, as touching the power supply portion of such a board may induce electrical shock.
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