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

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PSU and Video Card Diagnostics

A little history first, of course...

I recently replaced my video card in my iMac, as the 3rd LED light was coming on for a moment before initiating an endless reboot cycle.

After I reassembled my iMac, I noticed that it wasn't even getting to where I was before. The first LED is on and the 2nd and 3rd LED flash in unison and my fans give a little twitch when the LEDs light up. I unplugged the iMac and went over my connections to be certain everything was seated and plugged into correctly.

When I plugged in my iMac, there was a pop and a spark shot from my PSU. Undoubtedly this PSU is now toast...

but was the PSU the issue all along? Is it safe to assume that the video card I replaced had nothing wrong with it and the PSU just didn't have the juice to support it? And is there something else going on inside of the iMac that would cause the PSU to pop and spark?

Thanks for any help.

Answered! View the answer I have this problem too

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Is it possible to check voltage levels before going for the replacement?



After a lot of HW swapping it turns out the PSU that blew up was the initial issue and I had purchased an incompatible video card. My iMac now boots, but hangs on a blue screen before desktop. I suspect the previous owner had a problem w/ his OS installation so I'll work on that next. Good luck with your fix, jasonherek.


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First things first. Replace the PSU and see if all is well. Then address the video card issue.

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New PSU is on the way - will update when installed.


Replaced the PSU and learned a lot. All 4 diagnostic LEDS turn on and I hear the start up chime and all fans start to spin. However, I'm not getting a picture on the LCD display. To be more precise, I can see a backlight come on the LCD but nothing else.

USB devices respond to being plugged in (mice light up, iPad recognizes being plugged into a device) but no other sounds or images come on the monitor. I attempted to plug in a second monitor but it seems completely unresponsive ("No Signal") when using the MiniDVI to HDMI cable. Monitor can tell it's being plugged in to something but just "No Signal"s.

I'm down to LCD display or Logic Board. Any thoughts?

(Sorry if this isn't the correct way to respond to my thread - I'm new here!)


You need to make sure your external video rig works on a normal Mac, only then can you depend on its results.


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I am in the same exact spot as you. I just sent the video card to be "repaired'. It cost me $100. The original problem was when I powered on the IMAC I got the white screen and could hear the chime. I ordered 2 different brand new LCD screens, both gave the same white screen so I sent them back and sent the video card out. Now with the "repaired" video card when I power it on I get the chime with a BLANK black screen and when I plug in an external monitor to the mini DVI connector I get nothing there either. I'm losing my mind with this thing. Let me know what happens when you put in your new power supply.

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The psu helped my string of hw issues to get me to the point you are now. I ordered a new logic board and when it comes in I will update the thread and let you know if the logic board ended up being the issue. I'm glad you attempted to see if the LCD worked and sorry to hear it didn't. I wasn't sure if it was my LCD or logic board, but now I'm certain it's the board. Will update in the the next week or so.


Well today I tried a few things to see what would happen and learned a couple things, well read them but don't know how to apply them. 1st) I pulled the power cable, held power and drained IMAC for 10 seconds, plugged in external first and then power plug, when I turned IMAC on I only had 3 LED lights lit. Turned it back off, drained the power again, next boot without the external plugged in through the mini dvi and now I had all 4 lights again. So that was weird and no image no where so far. I changed out the inverter cable on the LCD screen to, no change. 2) The service manual says "When you replace the video card the first thing you have to do is re-install the firmware". I'm wondering if its because I don't have the correct firmware in there . Could that be why I'm getting a black blank screen? I went from a white / grey screen before the video card was repaired, after repair now I have a black blank screen. I don't know what else to do. I can't afford to keep ordering parts just to try them to see what works. Yes please let me know what happens when you get yours to show an image after you put in the new logic board. Also, having replaced 100's of motherboards in laptops and other PC's over the years, sometimes when you order a logic board or motherboard the BIOS aren't scribed on then. I hope you ordered a used one that's working and not a brand spanking new one. This happened to me with some Toshiba laptops recently. I ordered brand new boards because they were priced cheap and when I got them they had no BIOS scribed on them.


Can you tell if you have at least a backlight for the lcd after booting up? that's how far I got before I ordered my part. I also have read about needing to reinstall firmware, however, I have also read that it isn't always necessary (unfortunately I cannot cite anything - I've read so many articles trying to diagnose this it was in one of them). I ordered a logic board that the seller claimed was "pulled from a working mac". It's still a few days out, but I will definitely reply as soon as I make the repair. Hopefully this is the last leg of diagnostics involved. The guy who I bought the iMac from (bought it busted real cheap to learn how to fix iMacs) said he had someone tell him it was the video card, someone else said logic board but he didn't get a definitive answer. I'll be in touch.


before I sent the video card to be repaired I was getting a white / grey screen upon bootup. The repair guy messaged me when he got the video card that it wasn't working when they checked it and after he reballed the chip IT WAS working fine. After I installed it and got the blank black screen I told him this and he said that the chip might be bad on the video card and I might need a new one at $100 more. Well why would he so easily suggest this if he fixed it originally? I know if I fixed something I wouldn't just be like "oh I checked it and it worked after I fixed it, but maybe the chip is bad". If the chip was bad it wouldn't have worked when he checked it. So in a nutshell, I'm hoping it is the firmware and right now I'm trying to figure out a way to burn it onto a disc and get it to work. Don't have another Mac computer here to make a disc. Also, I don't have a backlight on as far as I can tell. Is ther a way to see if its on and just not working?


Just replaced the logic board - no change at all. Feels like a waste of $200 on the logic board and a good amount of labor at that. The machine has a new video card, new logic board and a new power supply. I feel like I'm overlooking something absurdly simple. I want to try this firmware upgrade, this may be what happened and my logic board may have been completely fine.

For the blank screen, I can tell there's a backlight on if I look at it from the side in a dimly lit room, usually comes on around the same time I hear the start up chime. I'm going to look into this firmware upgrade more and I will get back to you with my findings. Good luck on your end.


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