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Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo processor

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No chime after turn on and no status LED's

I have a lovely but elderly iMac and it doesn’t get to the chime when you turn it on. With the screen dismantled from the computer the fans turn fully on as expected, and connecting the screen temp sensor quietens them. Voltages on the pins for the PSU appear odd - pin2 and 9 is 3.5V to 3.8V. Pins4, 10, 11, 12, 13 are at 12V and pin 6 is at about 13mV. Non of the logic board status LEDs is illuminated. I can see them but there is no signal from any of them… any thoughts?

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Hello! Is the iMac able to boot into Mac OS?

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@bobsinger

Sadly not, black screen and no amount of keyboard action has enabled a prompt. When it first failed it took a while to get to the chime but the machine was inoperable. There are signs of life with the HD spooling up and the fans working but that’s it. Most interesting is the lack of LED’s though. Thanks for your interest.

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@moftyinmeysey I have had a very similar problem happen with one of my older iMacs. This sounds like either the power supply is dead or the motherboard is shot as there are no status LEDs at all. I would recommend first taking out the hard drive and backing up any data on it.

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@bobsinger Thanks again Bob, all backed up so all is safe but what next with determining the route cause? Are the pin out voltages as expected on the PSU? cheers.

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@moftyinmeysey They do seem a bit odd. Try checking the logic board test points. Here are the pinouts: https://guide-images.cdn.ifixit.com/igi/...

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In conclusion, it is most likely that your iMac’s motherboard has failed. The voltage readouts on the motherboard are normal, which indicates that your iMac is not turning on because of a component failure, or the motherboard failing. You may want to try to reseat components on the motherboard such as the processor, memory, and GPU. Otherwise, you will most likely need to replace your motherboard.

Here is a motherboard replacement that you can buy online: https://www.ebay.com/itm/164923592908?ep...

Here is an iFixit guide on how to replace your motherboard: iMac Intel 21.5" EMC 2308 Logic Board Replacement

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Martin Croft 将永远感激不已
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