Ghost Faults: Why Devices Misbehave and Then “Magically” Work Again

Ghost faults are intermittent problems: a machine behaves oddly or stops working, then—without any obvious fix—returns to normal. Because the fault is brief and inconsistent, it’s hard to reproduce and diagnose.

At a high level, ghost faults stem from two buckets:

1. External factors (environment, power quality, interference)

2. Internal factors (aging components, loose connections, micro‑cracks)

External factors (often the fastest wins)

• Power quality & interference (EMI/RFI): Voltage dips, line noise, or high‑frequency equipment on the same circuit can corrupt signals.

• Grounding issues: Poor or inconsistent grounding causes sporadic resets or data errors.

• Temperature & humidity: Out‑of‑spec conditions can push components to their limits.

• Vibration & static: Intermittent contacts and ESD events trigger rare, puzzling faults.

Field case (real world):In a busy office, a copier/fax unit produced garbled images and random artifacts—then worked fine for hours. Multiple boards and locations were swapped with no lasting result. During one failure, the room lights flickered for a fraction of a second. A deeper check showed a high‑frequency, high‑power machine on the building’s ground floor that was switched on occasionally, injecting heavy electrical noise into the shared supply. Moving the copier to a different electrical circuit (cleaner line) eliminated the issue. Classic external ghost fault.

Internal factors (often require a technician)

• Power supply aging: Electrolytic capacitors lose capacity; rails sag only under certain loads/temperatures.

• Intermittent cables & connectors: Slightly oxidized or loose terminals work… until they don’t.

• Cold solder joints / micro‑cracks: Heat expansion or vibration opens the circuit briefly.

• Thermal stress: Some components fail only when hot—or only when cold.

A practical diagnostic checklist

1. Log the conditions: time, workload, temperature, nearby machines switching on/off, any light flicker. Patterns are gold.

2. Rule out the environment: try a different outlet/circuit; if possible, use a UPS or line conditioner; check grounding/extension cords.

3. Reproduce safely: see if heat/cool cycles or specific workloads trigger the fault.

4. Inspect the basics: connectors seated? any bulging/leaking capacitors? burn marks?

5. Escalate internally: if still intermittent, suspect PSU aging, solder cracks, or marginal ICs—these typically need professional tools and experience.

Safety note: If you’re not trained, avoid opening power supplies or high‑voltage sections.

When to call a professional

If the device is critical, failures are tied to power/grounding, or you suspect internal component aging, a professional assessment saves time and prevents collateral damage.

In Florida, PCB Tech USA can help. We diagnose and repair industrial/medical/marine/HVAC boards and tricky intermittent faults. Contact: PCB Tech USA — West Palm Beach & surrounding areas.