in this video number {521} How to Repair Laptop Charger, No Power Solution, i demonstrated How to Repair Laptop Charger, No Power Solution. #Laptop #Charger #repairing - (DEAD) No Power Solution | How to Repair Switch Mode Power Supply SMPS, this laptop Dell laptop charger using UC3842 current mode smps controller ic, it had no power, when power was connected or plugged in, it was not powering ON.
when i checked the voltage on DC rail on bulk dc capacitor, these were 330VDC but there was no output. then i checked voltage on vcc capacitor there were no voltage. vcc voltage are the most important for function of any ic. so that was the reason that pwm controller ic us3842 was not taking start. (uc3842, uc3843, uc3844, us3845, ka3842,ka3843, ka3844, ka3845 ics have the same pinout in their datasheet). pin number 7 is vcc pin, it must have vcc voltage for 3842 ic, it must have 12 working vcc voltage. these vcc voltage were missing due to the reason that the startup resistor was burnt. it was not providing initial vdd or vcc voltage to the ic. i checked that the original resistor was 180K ohm. for test purpose i connected 310K Ohm. (we can use a higher value resistor, it will cause a slower start)
explained practical 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. after watching this video you can capable to:-
how to repair smps
fuse keeps blowing
how to repair switch mode power supply when short circuit at input
if SMPS is dead or no output
if SMPS have fluctuating output or output voltage unregulated
if smps have short circuit in output
how to eliminate short circuit
how to troubleshoot PWM SMPS controller when there is no switching from MOSFET
if SMPS have a whistle sound or excessive noise or excessive heat
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00:00 Introduction
00:27 UC3842 smps sample circuit
00:43 how to power up a circuit / use series lamp
02:14 how to troubleshoot fault in laptop charger
02:32 how to test switch mode power supply
02:57 how to test voltage on bulk smoothing capacitor
03:09 how to test vcc capacitor
04:04 how to test smps startup circuit

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