Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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Replacing graphics cards due to screen flicker

Since a week ago, my iMac screen started to flicker. Basically I see multi-color bands flickering up & down the screen. Sometimes it's on for a few minutes and then it goes away, sometimes it stays on and then after a while screen goes completely dark. When I power cycle, it starts fine and then does the same thing all over. I have read various threads online and it appears that this could be related to a bad graphics card.

Couple of questions:

1. On this model iMac, can the graphic card be replaced? I read that it's part of the logic board on some earlier models

2. What can I check before buying a new graphics card (assuming that's an option) or a new machine?

Thanks,

Bob

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Update:

I tried Dan's latest recommendation to disconnect the display cable and inverter from Power supply. I then connected an external display.

The screen is now flickering intermittently with either white background (Apple logo)/ black horizontal lines or mostly yellow & white screen flickers. Also LEDs 1, 2 and 3 are ON but 4 is off (as it should be since I have now disconnected iMac's internal display). Looks like I definitely have a bad video card.

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Sorry to hear the video card is bad as you know its a bit of work to get to and you will need to refresh the thermal paste as well (I would do the CPU as well).

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Many in this series have replaceable cards so your chances are good. It's a lot of work to replace.

You'll need to think this though are you up to the task and can you find the replacement card?

To test things out can you plug in an external display if you can see if the problem is present on it. If so its the card if not its the display its self.

Update

You'll need to inspect the diagnostic LED's, follow this IFIXIT guide: iMac Intel 24" EMC 2134 and 2211 Diagnostic LED's to see whats happening here.

Sorry to say your graphics board is gone, but your power supply maybe also bad here as well (given your symptoms). The LED's should tell you. - Good Luck!

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Thanks. I just bought the miniDisplay cable, hooked up external monitor and get nothing. I then hard booted my iMac, it restarted with the standard white screen and then and after a few minutes the screen goes black. Nothing shows up on my external monitor either. Does this mean by graphics card is hosed or is it my MLB?

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Thank you Dan. I will take a look at the link you sent. Spent some time on YouTube last night reviewing videos on how to change the graphic card. Looks quite involved and time consuming. I'm going to also call around tomorrow to get an idea of the repair cost. May be a wash to just go with a refurbed mini..

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OK-just took my iMac apart and checked the LED- per Dan's link:

LED 1- Trickle voltage from power supply- ON- working

LED2- MLB has good power- ON- working

LED3- Computer and video card communicating- ON- working

LED4-Computer and display panel communicating- On- initially when I power up then but then it goes off at the same time my display goes off (with the rotating wheel still spinning).

Here is the description of this LED:

LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

So it now appears it may not be my video card. Something has changed as I no longer can complete a boot cycle unlike the behavior when I first reported my problem.

Any ideas? Thanks.

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Lets try this, disconnect the internal display and the inverter from the power supply. Then using your external display see if you can boot up your system cleanly. If you can you know the inverter/display is pulling the voltage down so it's interfering with the rest of the system. If it doesn't boot up with the external display working then you may have multiple problems here. Do you have your system (and its peripherals) on a surge protector or a UPS? In any case you'll need to put some parts into this to isolate out the root issue. Maybe you need to find a second system which you can swap parts out with.

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Dan- Good suggestion. I found the internal display cable but am not sure which one is the inverter from PS. I took a picture but it looks like I can't attach it here. Is it the 1 1/2 inch cable that comes from behind the fan and connects next to the heat sink- right above the RAM slots? Thanks.

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bshakib, this is the inverter cable

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