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

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Why is my display blacking out?

A couple of years ago, my iMac's display started flickering. This progressed to blackouts for varying periods of time, until I could count on only few minutes of display before it would black out and not work again (even briefly) unless I left the computer off for an hour or two.

However, an external monitor connected it to has always worked fine (presumably ruling out the CPU or video card), and I've been using it in that mode since this started happening. Unfortunately, the external display isn't enabled in Single User Mode, which precludes using AppleJack, my favorite cleanup utility (at least through the Snow Leopard on this Mac; I miss it in Mavericks on my MBP).

When I presented these symptoms to the local Apple Genius Bar, the tech said the problem was likely a bad inverter, which would cost around $300 to repair if they did it, but the iMac had just exceeded five years old, and they would no longer touch it or even sell me the part (in spite of my having paid for AppleCare for three of those years, with no claims).

I subsequently replaced the iMac with a 2011 MacBook Pro, so it's been gathering dust, but I want to rehab and give it to my daughter. Can anybody confirm that the inverter is my likely culprit, or suggest other diagnostic tests? For instance, I've never heard the fan on this iMac except once or twice when the SMC went wonky and needed resetting. Could the inverter be overheating (say from a faulty fan controller and/or dust buildup) and kicking off, even though everything else seems fine? I just fired it up after having sat unplugged for many months, and the display is still on after an hour of use.

If I do need to replace the inverter, can anybody point me at a replacement part and procedure? Re the latter, I found one for a different model iMac, but it looks close enough that I can probably fake it.

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Try connecting to an external monitor to see if the external is showing the desktop. Also you can try using a flashlight aimed at an angle you should see a faint image of your desktop on the internal display. Tell us what you find.

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This could be a fault of the transformer on the inverter as well as any other part. Probably not caused by overheating. Right now, it does like the inverter. If you can provide the last four digits of your computers serial number, we could most likely find the right part for you.

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Thanks for the help, guys.

Dan, as I said, my external monitor (MiniDVI>HDMI) works fine (i.e. mirroring or extending the internal). As for checking for a desktop image, after several months' "rest" (unplugged), the iMac's display is also working fine; so far, I've had it on for a couple of hours with no flickers or blackouts. I suspect this recovery is temporary; I'll report results of the flashlight test if/when it blacks out again.

Oldturkey, my full S/N is W87510V9X89.

Ken

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2.4 GHz Core 2 Duo (T7700)

Intro Date: August 7, 2007 Disc Date: April 28, 2008

Order No: MA878LL Model No: A1225 (EMC 2134)

Subfamily: Mid-2007 - 24" Model ID: iMac7,1

Std RAM: 1 GB Std VRAM: 256 MB

Std Storage: 320 GB (7200 RPM) Std Optical: 8X DL "SuperDrive"

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Let us know when and if it fails. Monitor the temps etc.

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What do the diagnostic LED's show? right now it sounds like an inverter issue.

update

To Access the LEDs:

Follow the take apart instructions to remove the memory 1. access door and front bezel.

The four troubleshooting LEDs 1, 2, 3, and 4 (numbered bottom to top) are in a column 2. located to the right of the memory slot. Move the hard drive data cable to view the LEDs.

LED #1

Indicates that the trickle voltage from the power supply has been detected by the main • logic board. This LED will remain ON whenever the iMac (24-inch) is connected to a working AC power source. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power source is disconnected or the power supply is faulty.

LED #2

Indicates that the main logic board has detected proper power from the power supply when • the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED #3

Indicates that the computer and the video card are communicating. This LED will be ON • when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

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.

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I agree with OT you got a bad inverter

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Same here, inverter. I've replaced several on this model and it's an easy to medium effort rated repair. Just remove the optical drive and two screws in the inverter and plug a new one in.

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Okay, it sounds like the consensus is that it's most likely the inverter. OT, what should I be looking for in the diagnostic LEDs to prove/disprove this theory? If it is the inverter, can you provide or source one for me? Price?

Mayer, I couldn't find an iFixit procedure for inverter replacement on my model, but I did find one for the preceding (albeit 20") series:

iMac Intel 20" EMC 2133 and 2210 Inverter Replacement

Is this similar to how to get at mine, or are there gotchas not covered here? If so, can you describe the differences or point me at a procedure for mine?

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The bad part here is that the inverter board is apparently built into the back of the panel.

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I may be working on one of these today. I'll get back to you later today.

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Hello, thank you all for this thread. My computer is iMac 24" A1225 mid 2007. It has the same problem. Total blackout on the display. But the external monitor connected to the Mini DVI port works. However, the display on the monitor only last about 4-5 minutes before it turns black. The fan works very hard too. The LED #4 is off, and the rest three are on. Your expertising inputs are appreciated.

OS 10.10.5

Imac 24" mid 2007

2.4 GHz intel Core 2 Duo

ATI RadeonHD2600 256 MB

4 GB 667 mHz DDR2 SDRAM

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kenh6 will be eternally grateful.
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