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Model A1200 with 2.16 or 2.33 GHz Core 2 Duo processor

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Bad Display / Graphics Problem with iMac 24" 7300GT


hoping someone can help me with this.

So I assumed the problem was a faulty video card (7300GT) so I bought a new one and fitted it, correctly as I've done this a few times before.

However I'm still getting weird artefacts on the screen, thinking about it they ar different to the ones you get with the GPU overheating/solder problem on these machines, and shouldn't have bought it so quick. anyway..

See the attached screenshots (a combination of red and blue repeating patterns across the screen that redraw whenever you alter the display, i.e. move a window)

So, although not totally ruling out the video card I'm at a loss as to what the problem is.

1.New GPU hasn't helped

2.Artefacts appear on startup (Not software then?)

3.Don't appear to be heat related (SMCfancontrol makes little/no difference)

4. Known working LCD does not alleviate problems

5.Logic board in good superficial condition, I can't see any obvious problems.

6. RAM known working

7. Safe mode makes no difference

So hopefully someone can figure this out?

What I'm leaning towards is

1. Bad new video card?

2. Bad VRAM?

3. Bad GPU daughtercard?

4. Bad Logic board to GPU interface?

5. Bad logic board?

6. Power Issues?

7. LCD cable problem?

Many thanks in advance!


Forgot screenshot...

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Hook it up to an external monitor to help isolate the problem. If the artifacts are present on the external then the problem is hardware/video card related.

The 7300GT has a known issue with the capacitors on the card. The 7600GT was also an option for your iMac. They cost a bit more but you may consider it a cost effective repair vs the 7300gt loto.

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ABCellars - He stated he replaced the GPU unit (could be used Vs new) so its hard to see both units having the same problem. I'll agree using an external display would isolate if the internal display and its' cabling were having problems. - Good idea!


Yeah its a new GPU, however i put an old non working one in and it didn't display the red and blue artefacts. (it did display the usual symptoms of one of these cards gone bad and didn't boot properly)

However its leading me to think that the new GPU is defective.

Something also to note is that these didn't start appearing for roughly an hour after first putting it in, is it possible for a logic board to corrupt an otherwise good GPU?

I don't have an external I can use at the moment, but I do have two LCDs and both exhibit the problems.

Have examined and recleaned the logic board, unplugged everything apart from the essentials, even booted from firewire to see if the HDD was causing problems.

Such an unusual problem though.


Ben - I think ABCellars had a good idea using an external display. I would try that before going forward. If the external is OK it's the internal display or it's cable.


Yeah worked fine on an external. Waiting for a new card. Gave me the opportunity to bump it up to the 7600GT though so not all bad. Will update once it arrives.


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I had the same artifacts problem on my iMac 24" with GeForce 7300GT onboard, Lion 10.7.5; it started like in the pic quite a week ago and got worse day by day, till the system used to hang just after rebooting.

Once I could succesfully login I removed the GeForce kext (all of them) and it became usable after rebooting... but I obviously lost all the "video" capabilities, from desktop effects to movie playing as graphic acceleration had been dropped.

I reinstalled SL but it could not get any far than the language selection window... it crashed every time I restarted! artifacts were also visible during installation!!

So I opened my iMac! cleaned up GPU and processor from the old thermal paste and applied a new one; removed the dust off the blowers, put it back together...

Tadah! It worked like a charm!

after restarting the system I could go through the installation steps, then I installed a fan/temperature manager app (there are plenty of them, just google it!) and pushed CPU blower speed up to 2000 rpm...

it looks stable, no artifacts, no crashes.

I think I'm staying with SL as the problem started with Lion, and with Lion I also had my MacBookPro GPU fried after a couple of months I installed it... just a coincidence?

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I have quite a few MBP systems running Lion none have had any issues with GPU's failing do to the change. Yes, I've faced a few GPU issues with the NVIDA GeForce 8600M GT but that is not due to the OS (Lion or Snow Leopard) as there is a know issue with the GPU failing.


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If I didn't know better I'd think there was some signal leakage.

Did some one spray WD40 or something else onto the logic bds or cables. Did the video cable get damaged?

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Signal leakage as in electrical interference? or a faulty cable? I really don't think so, I used some iso alcohol on it but that wouldn't cause this would it?

In that case, would you suggest using different cable?

Some RF transmitter in the comp? should I unplug the wifi/bluetooth/infrared cables?


It also seems this guy had the same problem:

It's the only other occurence I've found on the internet though!


You may want to re-wipe the areas you hit with Iso-alcohol. You may have left a film which is slightly conductive. The area to focus on is the video part of the logic bd and cabling for signal leakage (forget the WiFi etc...). Did you forget to re-install any shielding or could you have put the wrong screw into the logic bd so it's touching something?


Do you try an external monitor? Did it have the same problem?


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Getting the same issue with an iMac using this GPU. It started right after upgrading the OS to Lion. Unplugging the computer for at least an hour "fixes" the system temporarily as it resets the SMC. Issue comes back and gets progressively worse over the course of a few days. For me, downgrading back to Snow Leopard was the "fix".

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You are correct there was a video driver problem with Lion (and claimed to be fixed in Mountain Lion) But, the symptom was different the system would crash with a Panic error when the video changed. That is one of the reasons I had wanted him to try out an external monitor as it would have ruled that out. In this case the issue was an internal monitor/LCD driver issue as the external display did not show the artifacts. If the GPU or software driver was the issue I would have expected the problem to be present on the external (which Ben states its not). You may want to give Mountain a try to see if that fixes your problem, if not you still have an issue that you should track down.


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Ben sera éternellement reconnaissant.
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