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Is there a way of testing the power supply on a Imac 21.5 late 2012 using a multimeter to see if the power supply is faulty?? I was wondering if there was a way to test it before spending money on a new one. Thanks jay. Update (04/22/2019) honestly thanks so much for the response, I was surprised I got any to be honest, if I getting no LED lights on the board , does this mean it’s getting no power from the power supply??? do these LEDs just light up when you plug the computer to a power out let??thanks jay
Before you remove the power supply from the system test the system out and review the onboard diagnostic LED’s
What does the onboard diagnostic LED’s telling you? LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement. Update (04/22/2019) No LED’s does imply the system is not getting power! Either from the outlet, power cord or the systems power connection and lastly the power supply could be damaged! Go to a local hardware store and get an 3-Wire Receptacle Tester so you can make sure the outlet is correctly wired and is properly grounded. You’ll also need to inspect the breaker panel to make sure the grounding line is properly secured to the metal water line or a grounding rod. Often overtime these degrade with corrosion. Check your power strip / surge suppressor make sure the onboard breaker has not popped or switched off. Often times when the breaker has popped a short occurred. Next try replacing the power cord to your system. You might want to invest in a good UPS or at least replace the surge suppressor as over time they do loose their effectiveness. If after all of this testing you can’t locate any issue is when I would conclude the power supply has failed. Do keep in mind a surge or a lighting hit could also have damaged your logic board as well, but you won’t know that until you’ve replaced the power supply
Hi there I have the same problem on the same iMac. I assumed it was a power supply issue and purchased a new PSU. I’ve installed the PSU and the machine is still not booting. When I have the screen off, no HDD, plug in the iMac and turn it on I am still not seeing any LEDs on the logic board. Do you think this is another faulty PSU (purchased from eBay) or could this be a logic board failure? Is there a way to determine which part could be the issue? Thanks so much for any advice! Luke
I would also like to know how to test the power supply. Sure I could buy another one from a good supply house per Dan’s suggestion, but I have 2 here now and I know the outlet and cable are good (works with other PCs and iMacs). What I don’t know is why I have no LEDs lit up on the motherboard. Can they be tested using a multimeter? Thanks.
