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The Power Supply Need Grounding

By on December 19, 2011

If you are repairing a switch mode power supply (SMPS) make sure the power supply board have earth ground connected to it. If you look at the photo of a LCD Monitor power supply, you could see that the earth ground is connected to the casing and the power supply board grounding connection did not attach to the casing because you want to perform the voltage test. In this case, if you put your black probe to the power supply board ground and try to measure the output voltages from the SMPS, there will be no reading. So you will think that the power supply have problem. You begin to inspect the power supply board this will waste your precious time. The moral of the story is to let you know that before you want to take any measurement in a SMPS you need to make sure the power supply secondary side is properly grounded.

smps grounding



  1. ec73

    December 19, 2011 at 4:19 pm

    I know It. In most power supplies there is no ground connection

  2. Vinay

    December 22, 2011 at 6:46 am

    Hello Sir,
    Can’t we put the black probe at negative point of any filter capacitor at secondary side of SMPS to measure the supply at secondary?

  3. admin

    December 22, 2011 at 10:37 am

    HI Vinay,

    The secondary side of filter capacitor is the same as the earth grounding line (cold ground).


  4. jgmanza

    December 22, 2011 at 3:51 pm

    Thanks for the heads-up.
    I am starting to troubleshoot an AOC 197-S Flatscreen monitor that shuts down after 2 seconds. So I am troubleshooting 2 seconds to black. But I was wondering about that.

  5. admin

    December 23, 2011 at 8:24 am

    Hi Jorge,

    One of the backlight have problem also could cause the display to shutdown after few seconds.



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