Thursday, March 24, 2016

Circuit board troubleshooting using handheld digital multimeters

Printed circuit board assembly troubleshooting


The printed circuit board assembly (PCBA) can be found in almost any electronic devices. These electronic devices range from consumer electronics such as scanners, exercise devices, charging stations, computer accessories and modems to commercial electronics in the industrial and medical fields with stringent requirements. Testing is crucial to ensure the electronic devices operate normally. In most cases of electronic device failures, the root cause is determined to be the PCBA itself. 

This blog describes some common techniques used in circuit board troubleshooting.  Before proceeding with the troubleshooting task, it is important to identify the failure symptoms. The failure symptoms may provide information about the possible cause of defect.

Checking the power supply voltage to the circuit

Voltage measurement of the circuit board’s power supply is an important testing process because it is critical that a proper level of power is supplied to most of the integrated circuits (ICs). It is essential to check if the voltage level output from the power supply is within the acceptable limit to prevent overheating or overloading of the circuit board. Handheld digital multimeters with 4 ½ digit display resolution deliver the precision, accuracy and repeatability which is compatible with the basic bench multimeters, would be a good alternative for the technicians to use in troubleshooting.

Visual inspection to look for burned or damage parts

Visual inspection is a straight forward and effective method for troubleshooting. Components or parts such as transformers, power output transistors, resistors and capacitors that carry the burn mark can be detected easily using this method. The burned parts normally appear as brownish in color and can be easily detected visually through the naked eye or with the aid of a magnifying glass. Sometimes, the overheated components will form a brownish mark on the circuit board and produce a burnt scent.


Figure 1 Example of dry joints with obvious crack line (figure extracted from internet)

Solder joint is another common item inspected during the visual inspection to look for any dry joints.  Dry joint is a common symptom of a defective board due to soldering defects. Dry joint cause poor contact at the solder joint and affects the current conduction in the circuit.  A good solder joint normally looks smooth, bright and shiny. Dull surface suggests a weak joint.  Dry joint can be checked using a handheld digital multimeter. Resistance test or continuity check is performed from one pin to another pin to locate any dry joints or open traces on the circuit board.


Next posting will discuss methods to detect hotspot for potential failure. 

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