How to Test Circuit Boards Using a Multimeter

When electronic devices encounter malfunctions, troubleshooting the internal PCBA board is a common method. These circuit boards are the core of device functionality; however, various faults may arise due to prolonged operation or external factors such as dust, moisture, or impacts. While some issues can be directly inspected with the naked eye, detecting concealed problems like short circuits, open circuits, or component failures requires reliable testing with specialized instruments. For general users, investing in expensive professional equipment might not be cost-effective. Therefore, using a versatile tool like a multimeter for PCB testing becomes an economical and practical solution.

What is a Multimeter

In the process of learning electronics, a multimeter is a crucial tool. It is a portable instrument designed for measuring electrical quantities such as current, voltage, and resistance. The basic components of a multimeter include a digital display screen, a function knob, and probes. During operation, the multimeter utilizes its internal measurement circuit to accurately obtain numerical values for the desired measurements. For example, in voltage measurement mode, the multimeter connects its input resistance to the circuit, and by measuring its resistance value, it calculates the voltage.

Multimeter measurement structure

How to Test Circuit Boards Using a Multimeter

Checking for Short Circuits:

  1. Turn off the power and set the multimeter to the continuity (or resistance) mode.
  2. Connect the black and red probes to the two ends of the circuit you want to measure.
  3. If the multimeter beeps or shows zero resistance, there is a short circuit in the circuit.

Checking for Open Circuits:

  1. Turn off the power and set the multimeter to the highest resistance range.
  2. Connect the black and red probes to the two ends of the circuit you want to measure.
  3. If the resistance reading is infinite, there is an open circuit in the circuit.

Measuring Resistance:

  1. Turn off the power and set the multimeter to the resistance mode.
  2. Connect the black and red probes to the two ends of the resistor, avoiding parallel resistances.
  3. Perform the measurement to obtain the resistance value on the circuit board.

Measuring Input and Output Voltage:

  • With the power on, set the multimeter to the voltage mode (pay attention to AC or DC).
  • Connect the black probe to the power supply’s negative or ground terminal and the red probe to the positive terminal.
  • Measure to obtain input and output voltage values.

Measuring Current:

  1. With the power on, insert the red probe into the multimeter’s current testing port.
  2. Set the multimeter to the current mode.
  3. Insert the black and red probes in series with the circuit you want to measure and perform the current measurement.

Ending

In general, the multimeter is an effective tool for testing PCB. However, it is important to recognize two issues: precision requirements and tedious work. To achieve the best testing results, typically a milli-ohm level multimeter is used, and each point needs to be tested individually. This is particularly disadvantageous for large-scale projects or high-density circuit boards.

Further Reading:

PCB Short Circuit Causes, Detection and Prevention

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