My iMac does not start up. I followed the light test to see if the problem is a bad logicboard. But I´m not sure, since the second light shows quickly and goes when I press the power button in the logicboard. So to be sure I want to test the power supply. I have a multimeter taht I´ve been using only to measure batteries and now want to try with the power supply. The problem is that I don´t know how to set it and use it. Sorry for my english

Thank you