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

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Display stays powered off at boot

Hello,

I've got an problem with my Mid-2010 27" iMac (A1312, EMC 2390, 3.6 GHZ, 12 GB of RAM, HD 5750 1GB).

When I press the power button it starts normally but the display stays powered off.

I tried to check with a light if it was a backlight failure but it's not. The display displays nothing at all.

I also tried to plug in an external display using a Mini Display Port to VGA adapter and I've got no signal too.

So I opened it yesterday and everything seems okay inside (I cleaned it too and now it's clean as a brand new inside).

So I checked the diagnostics LEDs: the #1 is normal, the #2 is on when the iMac is started and #3 and #4 never shine.

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So I've got several questions:

1 - Is my GPU totally broken?

2 - How to be sure it is worth the pain to buy a new GPU? Could the logic board be broken too?

Some pictures of the iMac:

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When you power the system do you get the startup tone?

If you do you know the main logic board is good and your issue is the GPU card.

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However, I tried to put the OS X 10.6.4 disc inside and I can hear the whole boot process from the DVD. It lasts several minutes and then the drive calms down. Then if I press Enter, I hear the DVD spinning and loading again (I guess it's the language selection menu of the DVD that pauses the drive until the user select its language with ENTER).

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2 Answers

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Attempt a reflow of the GPU before spending any money. Here's how:

https://www.youtube.com/watch?v=hoxR_TVE...

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Really? a reflow with a gas torch? thats a !&&* of a tech... In an oven I understand or with a heat gun but this... :))

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While this will work its only a stopgap solution as the solder under the chip has decomeposed from the high heat.

Basically, the tin in the solder has changed into a semiconductor state (crystallized). The idea here is to heat the solder hot enough so it reflows altering the tin back to a conductive state.

For the short term this will likely work. But! Once the tin has crystallized it tends to recrystallize again as some of the tin crystals are still present and act as a seed for the process to start again in a short time.

The only real way to solve this is to completely clean off the solder and apply fresh solder and hopefully a better solder that handles the high heat (hint: solder with some lead).

A second problem with tin is what is called tin whiskers as the tin crystallizes it tends to grow outward toward the apposing pole creating a short. Reheating tends to solve this as well.

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The oven fixed it so now I can say that only the GPU is faulty. I'm happy to see that the logic board and the others components are OK.

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Don't expect that oven fix to last long, but you know know where the problem is. The problem with baking is you really can't see when the solder flows and you have to do the whole board. It's pretty hit or miss.

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You're right, it already stopped working. But I know I just have to change the GPU to make it functional again.

I'd like to find a reliable one under 130 dollars. I don't care about performances. I just want to have smooth animations (mission control...)

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If reheating the GPU chip doesn't solve the problem you'll need to replace the GPU board. Finding a good working GPU card is getting harder in this series and they tend to be expensive as many people want to hang onto them. When I get home tonight I'll plug in the possible GPU boards your system will support here.

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Thanks, by the way, I don't care about the GPU performances, I'm a software developer. So I'd like to replace the faulty one with a cheap and reliable one.

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Here is your choices:

- ATI Radeon HD 5670, 512 MB - Apple P/N 661-5579

- ATI Radeon HD 5750, 1 GB - Apple P/N 661-5578

If you want smooth animations you'll want the 1TB board. I would also recommend you get TG Pro if you are gaming as you want to leverage the turbo mode so your card last longer. Remember this system was not designed for heavy weight gaming!

Your last choice here is modifying a 2011 iMac AMD Radeon HD 6970M 2GB Video Card to fit but that will set you back $900

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Romain Giovanetti will be eternally grateful.
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