Won't ever finish booting; logic board replacement?

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iMac Intel 27" EMC 2429

Modell A1312 / Mitte 2011 / 2,7 & 3,1 GHz Core i5 oder 3,4 GHz Core i7 Prozessor, ID iMac12,2

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jiclark @macdoktor

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Won't ever finish booting; logic board replacement?

Anyone ever replace a logic board in one of these babies? Is the part even available??

Thanks everyone, especially @danj. I'm going to urge my client to get a new machine, as fixing this one is just too problematic for a 12+ year old iMac!

Okay, so it turns out the client bought a new graphics card for this machine, and wants me to install it. Have any of you ever attempted this install, and if so, would you recommend I give it a try??

(Let me know if it would be better if I started a new thread on this.)

Thanks, John

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Unless it came from another iMac the MXM boards firmware will need to be updated which is a bit of a process. If it’s the same version then you can swap out the EEROM chip but you do need good soldering skills. Otherwise, you’ll need to copy the firmware off the dead board to then burn onto the new board (if different you’ll need to get the correct image from someone). If it’s not the same you may have issues with the heat sink fitting.

Even still what is this persons plans? Oftentimes they pushed the system to far with their workflow. Even I’ve done that three times! On my fourth board now and only write on it as much more will kill it again.

So consider your skills and time this will take to get working, also do you have the needed tools and lastly what if the board is not good either or won’t work as it’s not the correct board.

Saying no is not a bad thing if you have other work which is more profitable.

This system is on the edge of being useful with what people are expecting. So after getting it to work how long will it last?

8. Nov 2022 von Dan

Thanks (once again) @danj! I got an email saying you'd mentioned me in a comment suggesting I try Target Disk Mode to bypass the discreet graphics card, but I'm not seeing that comment here anywhere. Anyway, I tried it, and yes, the usual symbols show up on the screen. What does that tell us?

Your comments above are very helpful as well, particularly about the firmware issues. It really sounds more and more like this is a futile exercise!

8. Nov 2022 von jiclark

Try to put it into Target Disk Mode and find the Kext for the dedicated GPU and delete it, as this will make the Imac fallback into the intel GPU on the CPU

8. Nov 2022 von Thing

@macdoktor - look under Sqwerks comments as I posted that part there.

8. Nov 2022 von Dan

@thing - testing under Target Disk Mode will prove if the GPU board is bad or not. TDM uses the CPU’s integrated graphics to work which is why it’s a good test to isolate things.

Sadly, the IG services aren’t very good in this series if you are doing anything intense.

8. Nov 2022 von Dan

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Unless it came from another iMac the MXM boards firmware will need to be updated which is a bit of a process. If it’s the same version then you can swap out the EEROM chip but you do need good soldering skills. Otherwise, you’ll need to copy the firmware off the dead board to then burn onto the new board (if different you’ll need to get the correct image from someone). If it’s not the same you may have issues with the heat sink fitting.

Even still what is this persons plans? Oftentimes they pushed the system to far with their workflow. Even I’ve done that three times! On my fourth board now and only write on it as much more will kill it again.

So consider your skills and time this will take to get working, also do you have the needed tools and lastly what if the board is not good either or won’t work as it’s not the correct board.

Saying no is not a bad thing if you have other work which is more profitable.

This system is on the edge of being useful with what people are expecting. So after getting it to work how long will it last? — Dan
Thanks (once again) @danj! I got an email saying you'd mentioned me in a comment suggesting I try Target Disk Mode to bypass the discreet graphics card, but I'm not seeing that comment here anywhere. Anyway, I tried it, and yes, the usual symbols show up on the screen. What does that tell us?

Your comments above are very helpful as well, particularly about the firmware issues. It really sounds more and more like this is a futile exercise! — jiclark
Try to put it into Target Disk Mode and find the Kext for the dedicated GPU and delete it, as this will make the Imac fallback into the intel GPU on the CPU — Thing
@macdoktor - look under Sqwerks comments as I posted that part there. — Dan
@thing - testing under Target Disk Mode will prove if the GPU board is bad or not. TDM uses the CPU’s integrated graphics to work which is why it’s a good test to isolate things.

Sadly, the IG services aren’t very good in this series if you are doing anything intense. — Dan

oldturkey03 @oldturkey03 Rep: 784,3 Tsd. 1,1 Tsd. 894 2,3 Tsd. · Answer 1 · 2022-11-01T16:27:09-07:00

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oldturkey03 @oldturkey03

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@macdoktor since the removal of the logic board is not listed in the guides I figure we can at least provide you with some written instructions Model A1312 2011 Disassembly. As for the logic board itself, there are three for this model/year

661-5948 2.7GHz

661-5949 3.1GHz

661-5950 3.4GHz

If you do an online search by those numbers, you will find plenty of replacement boards available from lot's of reliable vendors.

@macdoktor since the removal of the video card is also not listed in the guides, we can at least provide you with some written instructions Video Card Removal

Video card for this particular model are the:

661-5967 AMD Radeon HD6770 512 MB

661-5968 AMD Radeon HD6970 1GB

661-5969 AMD Radeon HD6970 1GB

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Dan @danj Rep: 479,9 Tsd. Self employed contract worker 35 329 971 · Answer 2 · 2022-11-01T15:46:45-07:00

Dan @danj

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I would start off checking the onboard diagnostics LED’s to what they are telling you. Locate the LED’s about midway on the logic board with the display disconnected what from left to right which ones are lit when you power the system and press the power button.

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All four LEDs light up sequentially, from left to right, what does that mean, @danj?

1. Nov 2022 von jiclark

Just googled it, and it seems that all four being lit means everything is fine with the logic board? In that case, what's the next possible cause of the machine being unable to finish booting up (the progress bar takes forever to fill, but even when it's all filled in, it just stalls there)?

1. Nov 2022 von jiclark

@macdoktor - Sadly, it does sound like your GPU board needs replacement. This series GPU can’t support what many people throw at it for apps. Apple also didn’t size the cooling adequately. So after replacing the board you need to enhance the cooling by ramping up the fans RPM when running the system hard. I would get this great app as it allows you to visually see and log the systems thermals as well as set a point to push the fans harder TG Pro

The other possibility is a bad drive or one that is not correctly setup. If you have a second Mac create a bootable Sierra 10.12.x disk to see if that will but up when you go into Book Disk Manager using a USB wired keyboard and pressing the Option key to enter just after you restart your system.

2. Nov 2022 von Dan

Thanks @danj. I did try booting from several other drives, with no luck, so I'm fairly certain it's not that. You say "sadly", so what does a GPU replacement involve, or is it even possible? And yes, I'm aware of TG Pro; great utility.

This is a client's machine, and he just really likes this era of iMac, but I'm trying really hard to convince him that it's just not worth the trouble...

2. Nov 2022 von jiclark

@macdoktor - if you must then you’ll need this part iMac Intel 27" EMC 2429 Radeon HD 6770M Graphics Card or this one iMac Intel 27" EMC 2429 Radeon HD 6970M Graphics Card is the premium version. You’ll need to look online to find one and often these used ones are short lived too. Some folks have bake the board to get rid of the Tin cats whiskers these boards often had which only buys use a little time before they grow back.

2. Nov 2022 von Dan

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