Model A1224 / Mid 2007 and Early 2008 / 2, 2.4, or 2.66 GHz Core 2 Duo processor

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Is it a GPU problem or a Logic Board problem?

iMac mid 2007 20''

Yesterday I pushed the power button of my iMac mid 2007 but the screen remained black.

What I have done trying to solve the problem:

  1. I turned off the Mac and tried a SMC reset and PRAM reset. The first did nothing, while the second restored the loud boot chime (probably I had turned off the Mac with muted volume).
  2. I opened the iMac because I wanted to check the diagnostic LEDS. The first 3 LEDS were ON while the 4th LED was OFF. The third LED ON should tell me that the GPU is working fine and the fourth LED OFF should tell me that "the computer and the LCD display panel are NOT communicating".
  3. To check the GPU (that, according to the third LED, should work) I have connected an external monitor using a mini DVI cable. I couldn't get any signal, telling me that the GPU is having problems.
  4. To check the Logic Board I booted the iMac Volume on my Macbook in Target Mode. I succeeded to do so. Using Target Mode, I created a small Automator app that plays a song after start up. I shut down the iMac and turned it on again, letting it boot normally. It PLAYED the song, meaning that the iMac is booting fine.

To sum things up:

  • The third LED is telling me that the GPU is working. However, I get NO external video signal. This makes me think that it could be a Logic Board problem.
  • However the iMac seems to be booting fine! This makes me think that the Logic Board should be OK.

What do you think could be the problem here? Is this a GPU problem or a Logic Board problem? Thanks!

Answer this question I have this problem too

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95% of the time on this model it's the GPU. Not getting anything on the external monitor would also indicate that. Although I would like you to confirm that your external rig works using another Mac. Due to the high failure rate of the card, prices remain high. I have had great success using a hot air station on this GPU. The equipment is costly but you could try a hot air gun on its highest setting to give it a shot.

But before you go to this effort, please shine a flashlight at an angle to the screen and see if you can discern the desktop (please have it booted up). If you can, forget everything I just told you and replace the inverter.

Here's how to access it: iMac Intel 20" EMC 2133 and 2210 Video Card Replacement

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Comments:

Thanks for your answer Mayer. Actually I have already done both of the things you have suggested. The cable is working fine since I have tested with a friend's iMac. After booting up the faulty iMac I have used a flashlight too, but I couldn't see anything.

Probably, as you said, the GPU is broken. Do you think I could try to bake it in the oven (as an alternative to the heatgun)?

Thanks

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I have no experience with baking these in a oven. It scares me as the whole thing gets heated up. When I use a gun I can see when the solder flows and know I am there. I'm just not the guy to correctly answer this. The solder jobs I've done in my life have been with dental lab porcelain ovens with known melting points of the gold solder and very precise oven temperatures. Then with jewelry soldering. Again you could see when the solder flowed and you could draw the solder by moving the torch. You had hard and soft solders. Putting it a kitchen oven is more likely to destroy it than fix it, in my opinion. The job does not take long once the card is out. Call around and see if some has the equipment and the experience to do it right.

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Hi Mayer, just an update. I tried to fix the GPU card with a heat gun but I haven't had any success. I bought a replacement card from ebay US. It arrived yesterday. I have installed it and now everything is fine :) I've payed 90€ so I'm quite happy

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Repairing those does take experience and the right equipment. I'm glad you got a good price and got it running again.

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