Model A1312 / Mid 2010 / 3.2 GHz Core i3 or 2.8 & 3.6 GHz Core i5 or 2.93 GHz Core i7, ID iMac11,3

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Dead iMac, pinout PSU and hardware troubleshooting

Trying to change the CPU of my iMac from i3 550 to i7 860 somethhing is gone wrong. After trying to turn on the iMac it seems like it's died at all. No noise, no fan activity, no beeps, nothing when I press the On button.

The four leds on the motherboard are all switched off. Note that the AC source is ok, the AC cable is ok (tried 2 surely working), I checked connection between AC and power supply (there is a little noise like a spark when I connect the AC cord), I checked 50 times the connection between power supply and logic board. But I don't know how to verify the power supply, I don't have the right pinout and I don't know if in standby mode the PSU will give voltage to the pins.

I thought to play my Mac with new quadcore CPU, but I'm without my Mac at all... very sad.

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Any luck after changing the PSU, Paolo? My computer got the same issue, nothing is on when I pressed On button. I'm trying to fix my iMac 21.5 inch Late 2012.

No, sorry, still no luck for me :(


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Warning Paolo!

The PSU in the 27" iMac have a fuse. It's a little brown box just adjacent to the 120 V.A.C. Input on the PSU board. Just pull up the holder and the fuse is inside.

I have other problem in this way. (sorry my english! i´m argentinian :)


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Hallo riki lozada, thank you so much for your reply. It was really useful because I found the fuse but unfortunately I checked it and it's working.

So I'm still at the starting point... any others advices to check if the PSU is working or not??

Hola riki! Podrás decirme en dónde se encuentra ubicado el fusible, com alguna imagen? Hay algún número donde pueda llamarte? Soy argentino tambien


first thing to try would be trying to put the old CPU back in place. regarding PSU- it gives voltage to some pins, but not all of them (there should be at least 5v standby voltage to the logic board somewhere, even in off mode)


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Of course the first try is to put the old CPU back in place, but nothing changed: still died. The diagnostic LED 1 of the logic board was turned off, as the other 3 leds. I didn't find any voltages on the pins... the 5v in the logic board is somewhere, ok, but wich one? I can't try every solder point :-)

the standby 5v voltage is of course one of the cable pins going to the logic board :) but since no led is lit, i think something is with the psu - is there a fuse? that would be my bet - take out the psu and find a fuse and measure it. also take look at electrolytic capacitors if they are not "exploded"

No capacitors exploded, no black explosions in the psu, and if I well remember there is no fuse. I'll think to bring it to Apple assistance hoping in a psu substitution.

After solving this problem I will have to try again to put into my iMac the i7, and then probably the ssd like here: http://www.btobey.com/learn/imac-ssd-ins...


Sorry to let you know it this way, but 2010 i3 iMacs are only compatible with dual core i5s: the fastest CPU you can install is the 680. That's because your iMac's socket has slightly different electrical connections (FCLGA1156) compared to the one used on the quad core iMacs (LGA1156). Check ark.intel.com for more informations about the CPUs.

I don't know if this could have caused a shortcircuit to the logic board, but PSUs usually "snap" when have a failure, so if you didn't hear anything, maybe the problem lies somewhere else.


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I just checked and found that they're the same thing:

"They are the same thing. "FC-LGA 1156" is Intel's official name for the CPU package as it is a Flip-Chip Land Grid Array package with 1156 lands. All modern desktop CPUs (everything since the "Mendocino" PII-based Celeron) are flip-chip designs, so most people just call FC-LGA 1156 "LGA 1156." However, Intel makes a lot of other kinds of ICs that are traditional non-flip-chip designs and they feel they need to differentiate between what ICs are flip-chip and what ones are traditionally packaged."

(from here: http://www.tomshardware.co.uk/forum/2814...). So thank for your reply but I don't think this is the problem

And because that iMac in 2010 was sold wit i3, i5 and i7 CPU it is most probably that the logic board was the same for every mac... do you have proof to demostrate the contrary?

Parappa take a lool also here:

将iMac Intel Core i3 CPU升级到Core i7

and here:


So it seems that it is possible to do that without any problems. My iMac is dead because of my fault, don't know (yet) wich one


No my friend i just working today in my iMac, i replace the entire PSU but my mac stay dead. I´m searching info about the pinout of the PSU and i can´t found yet. You know some about this? (sorry, i´m argentinian people!) Best regards!


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riki lozada, what number is on your PSU? I believe it should be a 661-5468 which is a Delta ADP-310AF

Hallo Riki, sorry I still haven't found any psu pinout. I still have my iMac to be repaired. If I will not find any solution I will sell it for spare parts :-(

Hello Paolo, i´m stay in the same situation. The PSU have power 220 V.C.A. (argentina) in the inlet, have a 310 VCC after de rectifier bridge, but there are nothing in the Out connector. I supose that must be any pin @ +VCC, for the power on signal. I try to find this pin, but i can´t found any information about this. If U advance with ypur trouble, please, send me any info about!! Thanks Paolo!!! Best Regards and Happy new Year!!!

Riki Lozada

Hallo Riki, I gave the iMac to a friend who tested something and find the Psu not working, he ordered a new psu, I am waiting for it hoping that will solve.. Will let you know. Happy New Year!

Thanks Paolo. If yow have the oportunity to know wich is the pin for the Power On in the PSU, tell me please!!!


Hello guys i have a similar problem but i didn't change any hardware, my imac a1312 was full of dust so i just cleaned it and removed the old heat conducting material between the cpu and the aluminium thing between the fan but when i got everything in place it wasn't booting, a small fan activity take place every 5 seconds same as the mouse light.

Please help me with this problem


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Posting this after a VERY frustrating week on a customer's dead 2011 iMac 27".......

Hope it helps someone.....

Symptoms: iMac 'dead'...... no power, no fans, no chimes, nothing.

Try with new mains lead - nothing.

Open it up: Mains power tested & present at the PSU but no DC volt output & no diag' LED number 1 ( no standby trickle)........ bad PSU?.......

Tested start button was functional with multimeter.....

Tried shorting the two start button pins directly on the MLB socket........... Nothing.

Try machine in minimum configuration (i.e. disconnect the various peripherals in case a short is preventing the MLB starting up ) - NO difference.

Disconnect output multi-pin connector from PSU and test for DC outputs directly on the PSU output pins......... all pins at 0V........... bad PSU?.........

Changed power supply: - NO difference.

According to Apple diagnostic trouble shooting - now change logic board - not convinced this is an entirely logical step but had one here so did so - NO difference........... Aaaarrrggghhh !!

Out of frustration, resorted to opening up a working 27" iMac and testing the Power supply and MLB in that - where both work fine !!??

How can this be? - doesn't make any sense ??!!

Re-assemble machine's 'guts' and walk away from it until the next day........

Next day, after an overnight think, I disconnect mains connector from the PSU and temporarily solder a mains lead directly onto the PSU itself ( care !!), & make sure metal case has a solid earth connection ......... Result?........ Diag LED number 1 lit up (trickle voltage present) and machine fires up straight away !!

Diagnosis?......... faulty mains socket/filter........ it IS actually showing 240v at the PSU input pins ( measured via a multimeter) but presumably with no real power (multimeter possibly only seeing a misleading 240v induced voltage via a fried filter???), but hence PSU cannot actually operate.

Changed the filter/socket and machine is now fine...... all that and it was a £10 item !!

Moral of the story ?........ don't assume the mains filter must be OK because you can see mains voltage at the PSU pins........ also look for the required 12v and 5v DC being present on the output pins with the output connector disconnected; ( please be careful NOT to accidentally give yourself a 'belt' from the exposed 240v on the primary side) !

Repaired 100s of these iMacs but never had one with a bad mains socket filter.......... I presume this machine had seen a nasty spike / surge at some point before it came to me. At least the filter did its job and protected the Mac.....

You never stop learning in this game !


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