PSU Issues Testing Troubleshooting.

Good morning everyone. I bought an iMac project. I was aware that the computer had issues when I bought it, but I like a challenge. The issue is, it doesn't power on really. If you press the power button, you may be lucky and get a blurb of the Mac start up chime, but it gets cut short. There's no response from a screen and resetting PRAM/SMC hasn't done anything. So I opened up the iMac. When the power button is pressed, the fans start trying. Then they stop. Then each fan, one by one, goes then stops. I have located the diagnostic LEDs on the board, and they've helped. LED 1 is on, indicating trickle voltage is present. When the power button is pressed, LED 2 flashes while the fans do their thing, then once that cycle is complete it remains off. So! I have the PSU removed, and have searched high and low to see if there's a good way to troubleshoot it. There doesn't appear to be a good reference to what the pinouts and their voltages are. Also, do you guys thing the power supply is at fault, or the Logic Board? The Mac is obviously trying.

Thanks for your time!

Evan

Answer this question I have this problem too

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Were you told anything about its problems or history?

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No, other than it doesn't power on, and the ethernet port didn't work. I did get a decent deal on it and its accessories. It came with a magic mouse, brand new magic track pad, and the wireless keyboard. (all worth over $200) and it also came with a replacement board. Bought it all for $275. The guy had to move and didn't have the time or money for it.

I did swap the boards. On the non-original board LED 1 doesn't even light up, and the power supply actually makes a bit of a whiney buzzy noise now. I'm assuming its bad. So I shall replace it and hope for the best. If none of these things work I can well make back what I spent on it through parting it out I suppose.

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Deck the Halls
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Maybe this guide could help you troubleshooting the power supply. Just beware that switched power supply's handle high DC voltage and are potentially deadly...

iMac Intel 20" EMC 2210 Power Supply Output Voltage Test

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You won't know about the logic board till the power supply is working.

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I really appreciate this guide! The only unfortunate thing is, my PSU has 14 pins and this guide shows 10 pins. I did swap boards since this iMac came with a replacement board, and now the LED indicating trickle power isn't lighting up, and the PSU emits a strange sort of high ##&&% buzz. I'm going to take the risk and replace the PSU.

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evanpiveral will be eternally grateful.
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