How to Test a Circuit Board

August 25, 2020 Cadence PCB Solutions

Key Takeaways

  • A list of basic tools for circuit board testing.

  • Learn various ways to test a circuit board.

  • Explore PCB optimization ideas to aid future testing.

Digital multimeter with red and black probes on a black surface

A multimeter is a must-have tool for circuit board testing.

I am always excited to test drive a new car. I start revving up the engine and accelerating quickly just to check out if it suits my taste. Obviously, the salesperson isn’t impressed and is more concerned with whether or not  I’ll crash the brand new car. I’m not bragging but I have the utmost confidence with my driving skills, either in a new car or otherwise.

The same confidence is reflected during times when I need to test a circuit board. While there’s no steering wheel involved, I have other tools that help in identifying faults in the circuit. It can be a struggle but when you have a systematic test procedure you’re bound to locate the fault eventually.

Tools You’ll Need to Test a Circuit

You’ll need to be well prepared before testing a circuit. Here’s a checklist of basic tools you should have:

  • Analog/Digital multimeter.

  • Soldering gun.

  • Desoldering station.

  • Magnifying glass.

These are tools that will solve common problems like short circuits, broken traces, or faulty components. 

How to Test a Circuit Board That Stops Working

Start with a Visual Inspection

 A circuit board with a burn mark from a short circuit

Look for burnt components during your visual inspection.

When a circuit board suddenly stops working, there are sometimes obvious signs of what went wrong. You’ll need to rely on your vision to spot faulty components or broken traces. Often, circuit boards deployed in the field are damaged by electrical surges and there are telltale signs on the PCB.

Look for a burnt spot, particularly on the power supply module or I/O and connectivity ports. Pay attention to cracked ICs, broken traces, and blown capacitors. Sometimes, you could trace the damaged components by their acrid scent. 

Check the Power Module

If the components look fine, you’ll need to power up the circuit board. Measure the voltage of the power rails with the multimeter. Both the input and output of the voltage regulator need to show the expected values.

Check the fuse if the input voltage measured at the voltage regulator is 0V. If the fuse is replaced and immediately breaks after power-up, it means other components are shorted and draining a huge amount of current. 

A voltage of 0V, or below Vcc, at the output often means that the regulator or a component along the voltage rail has a short circuit. If that’s the case, the damaged component will heat up quickly. Bring your hand close to the components to feel if one is giving off excessive heat. Be careful to not directly touch the component when it’s powered on, as it can be extremely hot.

Remove the overheated components and confirm that the voltage has returned to the expected value. If voltage observed is still different than the expected voltage, there could  be more components that are damaged down the voltage line. Refer to the schematic and remove the next component that is near the edge of the PCB.  

If there aren’t signs of overheated components then look for broken traces. A broken trace could result in the voltage being detected at some points of the trace but not in others. Use your multimeter to narrow down where the discontinuity is. 

Check the Input/Output Ports

The I/O are also common points of failure. Damage on I/O ports seldom shuts down the whole circuit, but it usually results in anomalies in the system. For example, an alarm controller that always senses an open door even if it’s closed or a motor that is continuously activated.

If the I/O is protected by fuses, Zener diodes, or varistors, ensure that they are functioning well. If so, the logic IC or the microcontroller is likely damaged. The only way to find out is to replace the parts with good ones. 

Check Communication Ports

Circuit boards with communication ports like Ethernet and RS485 have an increased risk of failure. When communication failure is detected, check for burns or cracked communication ICs or protective components like Zeners. 

Optimizing Circuit Boards for Troubleshooting

A circuit board with visual indicators

Use visual indicators to facilitate testing.

Circuit board testing is a tedious process, particularly for issues like short circuits. However, there are ways you can optimize a PCB for future troubleshooting. For a start, you can create testing pads for voltages and critical signals like communications. It spares you from trying not to mistakenly short the neighboring trace with the multimeter probe. 

It also helps to add in LEDs as visual indicators for power, I/O, and communication. They help you to zoom in to the problematic areas with minimal probing.

Making these changes is easy with the right PCB design and analysis software. OrCAD constraint management rules ensure that the test points are placed in strategic areas and not mistakenly hidden by components. These are all things that can make your life as a designer and tester easier. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

 

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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