Our hospital introduced the Shimadzu SCT 3000TX CT scanner in 1989. The high-voltage secondary circuit of this device is equipped with a tetrode, and the high-voltage capacitor operates under a voltage feedback mode. In 1995, the cathode-side high-voltage capacitor (hereinafter referred to as "C2") suffered a breakdown. Due to difficulties in obtaining replacement parts at that time, we ordered new components while sending the faulty C2 to a repair service for maintenance.

1. Repair Verification and Initial Operation of the Capacitor

• Mounting Configuration: The repaired C2 was reinstalled on the original cathode side, while a new capacitor was installed on the anode side. Meanwhile, the original anode-side capacitor (hereinafter referred to as "C1") was temporarily removed for storage.
• Operation Check: The high-voltage circuit was activated, and the capacitor operated normally. A 15-day continuous operation test confirmed the stability and reliability of C2.
• Long-term Operation Plan: To maximize equipment efficiency, C1 was stored in an appropriate environment (with temperature and humidity control), while C2 maintained its operational status.

2. Re-failure of C2 and Challenges in Replacing with C1

• Abnormal Measurement Results: The measured capacitance was only 0.2μF, significantly lower than the nominal rating of 0.5μF. This indicated abnormal technical indicators and poor performance of C1.

3. Technical Background of the Capacitor and Repair Strategy

3.1 Operational Characteristics and Failure Mechanism Analysis of C1

• Excellent self-healing properties and a high-voltage design with a maximum rated voltage of 125kV.
• Responsible for two core functions in the high-voltage polarization circuit: voltage regulation and energy storage.

• "Physical state changes" due to long-term storage: The dielectric (polypropylene film) inside the capacitor may have undergone minor degradation during long-term storage, causing temporary capacitance reduction.
• Limitations of measuring instruments: General capacitance meters measure based on DC battery charging/discharging, which differs from the rated voltage and current conditions in actual high-voltage polarization circuits, potentially failing to accurately evaluate C1's true performance.

4. Charge Activation Procedure and Results for C1

4.1 Equipment Startup and Charge Activation Steps

4.2 Operational Confirmation After Activation

• Basic Operation Check: Verified kV positive-negative balance, checked for device errors, and performed normal warm-up procedures.
• Image Quality Verification: Confirmed exposure current levels and performed calibration using a water phantom. Results showed correctly generated scan images, stable instrument displays, and no high-voltage discharge or abnormal noise.
• Clinical Operation Check: CT scans of various patient body parts confirmed normal device operation, with image quality maintaining the same level as before the failure.

5. Lessons Learned from This Case

5.1 Economic and Operational Benefits

• Cost Reduction: High-voltage capacitors are core components of CT scanners, and introducing new ones requires significant expense. This case achieved substantial cost savings through repair of faulty components and activation of long-term stored parts.
• Reduced Maintenance Downtime: While external parts procurement often takes a long time, repairing and reusing existing components minimized equipment downtime and reduced impact on clinical services.

5.2 Technical Insights

• Activation Potential of Long-term Stored Components: Even if high-voltage capacitors experience capacitance reduction due to long-term storage, step-by-step charge activation in an actual circuit environment can sometimes restore them to rated capacity for normal use.
• Proper Selection of Measuring Instruments: Evaluating component performance requires measurement environments close to actual operating conditions. Rather than judging component quality solely based on general capacitance meter results, it's important to combine with operational tests in actual circuits.

6. Inquiries