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No Supply Voltage To Power IC?

By on February 16, 2009

powersupply

If you come across SMPS that have no supply voltage to the VCC pin of the Power IC, then there are four possible causes (assuming the fuse, bridge rectifier and filter capacitor are okay). The first one would be an open circuit in the start up resistor (high ohm resistor) that had prevented the voltage from going to the VCC pin of the power IC. The second one would be the VCC line circuit track open or dry joint . The third cause was Power IC shorted and the last cause was shorted corresponding components that are related to the Power IC. I came across a shorted ceramic capacitor (104 50 volt) that had pulled down the supply voltage.

If you need to isolate this problem, i guess the fastest would be by removing the Power IC and power on the equipment. For your information it will not blow the SMPS and after the removal of the Power IC and you get back the supply voltage, you can make the conclusion that it could be the Power IC had shorted or the corresponding components have problem. In certain cases you could also remove the switch mode transformer together with the Power IC and how’s the result like.  Its on your preference because in troubleshooting and repairing SMPS there are many methods to isolate a fault. Test on the methods that can give you the most accurate result.

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2 Comments

  1. Mihir

    September 23, 2009 at 4:02 pm

    i have an multi meter but i don;t know that how use it

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  2. admin

    September 23, 2009 at 9:40 pm

    Hi Mihir,

    Get my ebook TestingElectronicComponents.com as it has pictures to show how to use it.

    Jestine

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