Troubleshooting Tips

• Check the obvious and try the easy things first.
• Power: Switched on? Connected? Fuse blown? Correct voltage? Grounded?
• Probe all power and ground points. Check if polarity is reversed.
• Capacitors – check for reversed polarity of electrolytic caps.
• Shorts and open circuits
• Check for blown component
• Is op amp single or dual supply? Check the data sheet
• Measure test points with a scope or meter.
• Check one stage at a time starting at the beginning or input stage.
• Use an oscilloscope and voltmeter liberally.
• Generally, you can not probe across a resistor to get resistance when in a circuit. There are other things connected that will affect your readings.
• When measuring in current mode, your meter/probes should be placed in series with the circuit, not in parallel like when you test for voltage across a component.
• Scope probes: bad, 10x, type
• You might be grounding a part of the circuit through your test equipment. A floating or battery powered meter can be better at times, especially around diode circuits.
• Check and recheck pinouts and orientation of ICs, BJTs, FETs and other components.
• Use power and ground planes for power-related noise issues.
• Use bypass caps to reduce noise problems. See “Don’t bypass your capacitor” article
• Use heat shrink to avoid potential shorting.
• Check if your oscilloscope is in DC or AC coupling mode.
• Design: Check for power ratings, voltage ratings, etc.
• Reduce trouble area down to a smaller subsystem.
• Look at solder joints. Look for discolored components. Wiggle components. Resolder the solder joints.
• Smell the circuit to see if you can locate a burnt part. Take a thermal image.
• Touch to see if a component is particularly hot. BE CAREFUL!!
• Use freezing spray to cool down a component to see if it works.
• Deduce from the symptoms.
• Use logic and common sense but don’t jump to conclusions.
• Signal tracing: Start probing from first or last stage of the circuit and find where the signal goes bad or becomes good, respectively.
• In development phase, the reasons for a non-functioning circuit can be:
  • Faulty component(s) - circuit not hooked up correctly - incorrect design
• Blown parts due to static discharge, i.e. not grounding yourself when handling.
• Check the schematic (if available) and datasheets. Reread them.
• Ask! Ask an expert/technician/Jeff. Ask an advisor. Ask another student.

Some helpful troubleshooting links:

Troubleshooting – Theory and Practice

So You Made A Board and It Doesn't Work... Now What?

Troubleshooting and Repair of Consumer Electronics

The linguistics of electronics troubleshooting