V120 Amazing Fault, Simple Solution | CP Plus 12V 240W CCTV Camera Half Bridge SMPS Live Repair

SMPS Troubleshooting & Diagnostics
📌 The CP Plus power supply unit for CCTV cameras failed to start when a load was already connected, despite working normally if the load was applied after startup.
⚡ Testing revealed that the VCC pin (pin 12) of the control IC was receiving inadequate voltage (approx. 3V with load vs. 10V without load) during the startup phase.
🛠️ The underlying cause was a weak electrolytic capacitor connected to the VCC line, which failed to provide the necessary stable current for the IC during the high-load startup sequence.

Component Analysis & Repair
🔍 Diagnostic checks identified two capacitors on the VCC line associated with the auxiliary winding of the transformer; one of these had lost its capacity.
📉 The faulty 4.7 µF capacitor had degraded to roughly 2.9–3 µF, preventing it from holding the required charge to support the IC's duty cycle.
✅ Replacing the degraded capacitor with a new 4.7 µF/63V component immediately resolved the issue, allowing the power supply to activate reliably even with a pre-connected load.

Key Points & Insights
➡️ Understand VCC Stability: The capacitor near the IC's VCC pin acts as an energy reservoir; if it weakens or dries out, the IC cannot maintain the necessary duty cycle during the initial power-on phase, causing a startup failure.
➡️ Check Capacitance Value: Even if a capacitor looks physically undamaged, it may be "weak" (low capacitance); always use a multimeter to check the actual value against the rating.
➡️ Standard Fault Symptom: If an SMPS starts without a load but fails with a load, prioritize testing the VCC filter capacitors in the auxiliary circuit, as these are the most common points of failure in switching power supplies.

📸 Video summarized with SummaryTube.com on Oct 03, 2026, 18:01 UTC