How to Check Bad Circuit Boards

By John Papiewski
You can check many circuit boards with an oscilloscope

As circuit boards have become more complex, so has checking them for problems. However, many faults can be tracked down by checking connections and performing a visual inspection. If that doesn’t resolve the problem, obtain a schematic for the circuit, connect the circuit to power and test it with an oscilloscope. If necessary, use a signal generator to check portions of the circuit. By tracing through the circuit from beginning to end, you can isolate the problem. Your troubleshooting skills will improve with practice and patience.

Examine the circuit board closely for tell-tale signs of component failure. Parts may have burned and become discolored or burned the board underneath. Look for swollen or cracked capacitors. Turn the board over and carefully check the traces for scratches and other damage. Also check for solder bridges—blobs of solder that short-circuit adjacent traces or pads.

Remove and reseat all integrated circuits (ICs), connector, and any socketed components. Check larger connectors for signs of corrosion. Edge connectors, the part of a circuit board that mates with a card connector on a motherboard, are susceptible to corrosion. They can be cleaned by rubbing a pencil eraser on them, then wiping them clean.

Study the circuit board’s schematic. Note the locations of positive, ground and negative power and active components. The schematic may show test points and signals or voltages that indicate normal circuit operation.

Connect the circuit board to its normal source of power and turn it on. Connect the oscilloscope’s ground clip to the circuit’s signal ground. If the circuit produces its own signals, trace it with the oscilloscope probe. If you choose your test points carefully, you should be able to isolate the problem quickly.

If the circuit generates no signal of its own, set the signal generator’s frequency, amplitude and waveform to match what your circuit needs. Connect the generator's ground to the circuit’s signal ground. Inject a signal at critical points in the circuit, for example, at an amplifier or filter input. Probe the circuit with the oscilloscope. By methodically tracing through the circuit, you can isolate the problem.

Warning

Be aware of any hazardous voltages while the circuit is powered on. Do not work around exposed 110V AC unless you’ve had experience working on circuits.

About the Author

Chicago native J.T. Barett has a Bachelor of Science in physics from Northeastern Illinois University and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."