in this theory and practical tutorial i explained practical functional description to Understand & Repair Switch Mode Power Supply SMPS Practical troubleshooting. it is using FSDH321 current mode SMPS PWM controller. DH321 & DL321 are similar ICs but the main difference is switching frequency. Pinout is same. br i demonstrated How to repair switch mode power supply SMPS very easy. i shared my easiest and perfect troubleshooting techniques practical troubleshooting. smps concept and troubleshooting repairing or understanding repair switching mode power supply basics and working principle. also i discussed smps basics.