Model A1200 with 2.16 or 2.33 GHz Core 2 Duo processor

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Troubleshoot Display Black boot from DVD

1. Wife reported display with abnormal characters, and eventually going black

2. Apple Store Genius diagnosis as GPU Assembly failure

3. Purchased refurbished GPU Assembly from DV warehouse, tested by DV ok, 90 day warranty

4. Installed refurbished GPU

5. Power-on after installation.

6. 1st attempt to load Mac OS X from DVD to internal hard drive Disk (replaced internal hard drive since we had the computer completely opened), installation proceeded normally, then display goes black, computer appears to be still powered on.

7. Next attempt, display goes black within a few minutes.

8. Went to Apple store, recommendation to use an external monitor

9. Installed external monitor

10. Powered on, using external monitor, booting from install disk

11. Apple chime, dialog windows prompts to install OS, everything proceeding normally.

12. Apple desktop display showing on internal monitor and external monitor

13. Mac OS X installation progress bar is displayed on the internal monitor, gets down to 28 min.

14. External monitor displays just the desktop background

15. Internal monitor goes black.

16. External monitor goes black.

17. External monitor sync goes from green to amber

So, what should I focus on next to isolate the problem?


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OK, I'm going to send the refurb'd GPU back to vendor for a replacement. We'll see how long this will take. thx.

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Round 2.

Installed second GPU assembly from vendor. Probably a refurbished unit. Results are the same as seen in the first refurbished unit from the same vendor. I had moved the original internal hard drive to an external enclosure since having to change the GPU opened up access to the hard drive. I had installed a new Seagate drive in the internal drive location. I then connected the original hard drive installed, now moved to an external firewire 800 enclosure and tried to boot from the external drive. I used a startup disk power-on option to select the external drive.The system just went to a white internal screen display and never booted. The display went white for a long time, never got a signal to display an image, but, it never went black. Why does it go black when installing from DVD, but not when trying to boot from external drive? I'm going to reset the SMT to see if that has any effect. Another suggestion was to re-install the original internal hard drive, I'll try that after the SMT reset .

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Round 3

Getting desperate.

Put the original hard drive back in. Nothing was originally wrong with it, just wanted to upgrade capacity. So, the only difference now is the iMac has the second refurbished GPU assembly installed. Now, I just have enough time to log in to an account and the internal display goes black. When I was booting from an install DVD at least the display would be getting a signal for 17 - 20 minutes.

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Round 4

Booting in Safe mode, the display is more stable and does not go to black as frequently. I need to repeat this on multiple starts to confirm. But, now I've noticed another problem, since I had the computer opened, I decided to change the PRAM battery. But I screwed up and broke the bottom flange that hold the battery in place. I put electrical tape on it to try and hold it in place, but it's not a tight fit and the battery appears loose. So now I've introduced another variable. I'm going to try and figure out how to hold the battery firmly in place.

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Fixing multiple problems at the same seems like a good idea if it works. In your case it didn't. Put the old, known working, hard drive back in and solve the GPU issue first, then go for the hard drive upgrade.

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I would talk with your vendor and see what they think (I think you need a different GPU card).

If this answer is acceptable please remember to return and mark it.

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It's possible GPU is not correct part, but I was careful on order. It's 661 -4180 Nvidia GeForce 7600 GT

I found a iFixit ques/answer. Now I have more info

1. Power-on, all 4 LEDs are light, screen displays images, and I enter selections to start Mac OS X installation. Installation proceeds normally

2. About 20 min., LED and internal display goes black

3. CD/DVD drive continues to turn for a few minutes and then eventually stops

4. Info from other ques/answer

5. LED 3 green - computer/video card communicating

6. LED 4 black - computer/LCD display not communicating.

7. Computer/LCD display communicated for a certain time interval (also communicated with an external display in earlier trials).

8. Then, computer/LCD display stop communicating with both internal and external displays and they go black.

9. Something is failing to get a signal to the displays after a time interval. Is a part on the edge of failing, and when it heats up it reaches a threshold and fails?

10. What options on what that part would be?

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If I understand your symptoms everything works/looks fine on external and onboard display for a time ~20 min then both fail. With only LED 4 going dark. However AFAIK the only thing that could cause the external video to fail is the GPU… even if the iMac thinks it's still "communicating" it's not delivering an image to either… so IMHO it's back to bad GPU.

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