{1057} Why 400V Capacitor Failed in 420V PFC Circuit | MFA420PS48 XP Power | Root-Cause Analysis

This video (Episode 1057) is the follow-up to my previous repair video {1408}, where I found a 400-volt capacitor installed in a PFC booster section running at around 420V DC inside the MFA420PS48 XP Power supply, used in Planar MG2-PS3R video wall modules.

Although the capacitor measured OK on the meter, it failed inside the power supply under real load.
In this follow-up investigation, I:

Fully disassemble the capacitor

Remove the winding and inner layers

Inspect the aluminum foil and dielectric

Identify heat marks, stress points, and insulation breakdown

Explain why a capacitor can measure good but still fail in a PFC stage

Discuss how under-voltage-rated capacitors fail prematurely in high-voltage PFC booster circuits

This video provides a deep root-cause analysis for technicians repairing SMPS, industrial power modules, and XP Power products—especially where poor component selection or marginal voltage rating causes long-term reliability failure.

Power Supply: MFA420PS48 (XP Power)
Module: Planar MG2-PS3R
Fault: 400V capacitor used in 420V PFC section → premature failure
Conclusion: Component rating margin was compromised

Watch the previous video (Episode 1408) for the full repair process.


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