Touchscreen Blue Screen Issue in CNC Machine Due to Poor Grounding – A Real-World Case Study

Problem Description

A CNC lathe, which had been operating reliably for several years, suddenly began experiencing intermittent touchscreen display issues. The HMI (Human Machine Interface) touchscreen, acting as the upper-level controller, communicates with the inverter to regulate the spindle motor speed.

Fault Symptoms:
During normal operation, the touchscreen would frequently display a blue or scrambled screen.
The inverter's real-time data (e.g., speed, current) became invisible or unreadable.
Power cycling the system temporarily resolved the issue, but the fault reappeared within minutes.
 

Troubleshooting Process

Initial Checks:
Verified inverter wiring, external control circuits, and overall machine condition — all were normal.
Replaced the inverter with a new unit; the issue persisted.

EMI Mitigation Attempts:
Replaced control wiring with shielded cables.
Lowered the PWM carrier frequency of the inverter.
No improvement observed.

Touchscreen Isolation:
Unplugged and reconnected the touchscreen power — fault disappeared temporarily.
Disconnected all signal cables from the touchscreen — blue screen still occurred.
Conclusion: The issue was not caused by communication line interference.

Grounding Inspection:
Upon close inspection, the grounding wire of the touchscreen was found to be loose and corroded at the connection point.
Removed rust from the grounding terminal and resecured the grounding wire with a bolt.
 

Solution

After properly grounding the touchscreen, the system was powered up again. The touchscreen operated normally, and the blue screen issue did not return, even after several hours of continuous operation.

Root Cause Analysis

The root cause of the blue screen was poor grounding, which led to:
High ground resistance, and
Electromagnetic interference (EMI) affecting the touchscreen’s internal circuits.
This case highlights that effective grounding requires:
A secure mechanical connection, and
A low electrical resistance between the device and the earth.

Key Takeaways

Intermittent display issues in CNC systems may not always stem from communication or inverter hardware faults.
Grounding quality is critical in high-power, high-frequency environments like CNC machining.
EMI-related symptoms (e.g., blue screen, flickering, data loss) can often be resolved by improving system grounding.

Conclusion

This case demonstrates the importance of system-level diagnostics, especially in complex electromechanical systems. A simple grounding issue, often overlooked, can lead to persistent and puzzling faults. Ensuring low-resistance, corrosion-free grounding is essential for stable operation in industrial automation environments.