Troubleshooting Tips
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?