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Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo processor

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Internal monitor not working after graphics card was replaced.

We recently replaced the AMD Radeon 4670 256MB graphics card in our Late 2009 21.5" iMac. ( Prior to replacing the graphics card, we had discolored stripes on both the internal and an external display. Therefore, we determined that the graphics card was at fault. Also, this particular model has an actual discrete graphics card, not just integrated graphics.

Everything seemed to go well with the repair. However, when we turned the iMac back on, the monitor would not come on at all. The computer chimes and does actually boot up. We can tell this, because we plug in an external monitor and it works flawlessly. Once the computer gets past the boot screen, diagnostic LED 4 finally comes on and the backlight comes on, but there is no picture at all. To be clear, diagnostic LED 4 does not even come on until the OS is fully booted (to the login screen), but the external shows everything from the moment the iMac is turned on. From my past experience, LED 4 comes on almost immediately after the chime.

We've reseated the graphics card, and quadruple checked all of our connections. We happened to have the exact same model of iMac (minus the discrete graphics card) in our office, so we even tried a different monitor, vertical sync, and LVDS cable. Nothing changes the symptoms at all.

At this point, we're completely stumped on what to do next, or what the issue could even be. Any help at all would be GREATLY appreciated!!!!

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was eBay the source for you new video card?


Sorry for the delay in response, but no, eBay was not the source. An actual vendor for Mac parts was used.


Hey Curtis, obviously a year later here, but I wondered what your final result was on this. I'm having a similar issue w/ a 2011 iMac 27". Unfortunately, I don't have an equivalent machine to test parts between. And I don't get any backlight or content on the screen (shining a flashlight on it shows nothing). But Sys Profiler shows both the new GPU and the display. And external displays work fine.


I am also very curious about this. I just changed out my graphics card and having the EXACT same issues... to a T. I would like to hear what was the end result.


ANy update as to the cause as we have the same issue?


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Ok! Please plug this monitor in another working computer. Your problem should disappear.

It seems it is the monitor, also check all cables thoroughly.

I would exchange this monitor.

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How do you about doing that?


Hey dmsmakemusic43,

I'm not sure if you noticed in my original post, but we've tried a different monitor that is known to work in a different iMac, and it doesn't work either. Also, if we take this monitor and put it in the other iMac, it works perfectly. The monitor is not the issue here. We tried another graphics card, and it didn't work either. At this point, we determined that the logic board was at fault. We've verified that we have the correct part number for the video card, and it still doesn't work.


I assume you did not try swapping the LVDS cable out. Other than that I would think the connector on the V-Sync cable would be bad. A definite head scratcher :-}


I did try swapping out the LVDS Cable and the Vertical Sync Cable. Both were on the other monitor that we tried, and we also bought a new Vertical Sync Cable because the gold contacts were bent out of shape.


Could you have zapped something (ESD)? If you've changed out everything other than the logic board, sync/LED board & power supply one or more got damaged somehow.


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Curtis Fox zal eeuwig dankbaar zijn.

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