A machine can generate alarms, overloads, missed sensors, and sequence timeouts because something mechanical is binding. Electrical symptoms do not guarantee electrical causes.
Five Principles to Use in the Field
- Use your senses safely. Abnormal sound, heat, vibration, smell, product marks, belt tracking, and visible wear provide high-value clues.
- Check freedom of movement. With proper isolation, determine whether shafts, guides, rollers, linkages, and actuators move as expected.
- Inspect recent work. A tightened guide, replaced bearing, adjusted stop, changed format part, or cleaning operation may be directly related to the new fault.
- Think about load path. Ask what physically resists the motor or actuator. A downstream jam may appear as an upstream electrical trip.
- Look for progressive change. Mechanical failures often worsen gradually: heat rises, vibration increases, cycle time lengthens, or current drifts upward before the final stop.
Pressure Mistakes to Avoid
- Resetting overloads repeatedly without checking why current increased.
- Assuming a sensor timeout means the sensor is bad.
- Replacing a motor when the driven equipment cannot rotate freely.
- Ignoring fasteners and alignment after recent maintenance.
A Practical Breakdown Method
- Review the electrical symptom but do not stop there.
- Identify the mechanical load connected to the affected actuator.
- Inspect for jams, misalignment, wear, and interference.
- Compare temperature, vibration, and movement with a healthy reference if available.
- Correct the mechanical cause.
- Verify electrical load returns to normal after repair.
Scenario: A servo repeatedly faults on following error at one position. Electrical checks are clean. With power isolated, the slide becomes noticeably tighter near the end of travel. A damaged linear guide creates the resistance. The servo fault is accurate: commanded and actual motion diverged. The mechanical cause created the automation symptom.
Train This Before the Next Callout
Choose one critical machine you know and apply the ideas from this chapter while it is healthy. For mechanical faults that look electrical, write down the normal sequence, the key evidence you would want to preserve, and the first three checks you would make if the machine stopped. Then compare your plan with the electrical drawings, PLC diagnostics, maintenance history, and the experience of another technician. A ten-minute rehearsal in daylight can remove several minutes of confusion at night.
3 AM Rule: Whenever current, timing, or position becomes abnormal, inspect the physical load before condemning the controls.
Chapter Checklist
- Can I describe the symptom without naming an unproven cause?
- Have I preserved the evidence that could disappear after a reset or restart?
- Do I know which system boundary I am testing next and why?
- Have I kept safety controls and temporary changes visible and controlled?
- Can I explain my current facts, hypothesis, and next action in under thirty seconds?