Video issues with iMac 20"

I have a client whom has a 20" iMac running 10.6.8 with 2.16 C2D CPU.  The problem they've been experiencing is sometimes there will be a diagonal line in the screen that just appears and it will not go away until the system is restarted.  When playing Hulu and other video the video will sometimes freeze and the sound will continue.  Shortly there after the sound stops and the entire machines freezes.  Only way to correct this is to hold the power button down and then turn it back on.

I've had the machine for a day now and have not been able to recreate these issues.  I've tested it with the Mac diagnostic mode by holding the D key while booting.  The short and extended test finish with no issues.  

I have a hunch these issues are related to the video card but I don't know how to stress the card in a Mac.  First thing I've done is remove all dust from the machine.  Thanks in advance.
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1namylnAsked:
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Eoin OSullivanConsultantCommented:
Try something like NovaBench (http://novabench.com/) or XBench (http://xbench.com/) to put the graphics card through its paces ...it might be able to re-create the issue.

I'd agree with your diagnosis that the graphics card may be at fault and in a PC a few years old it can start to fail.
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1namylnAuthor Commented:
I also test the memory using UBCD.  Found no issues.
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strungCommented:
The Mac came with a hardware test on the install CD. See:  http://support.apple.com/kb/HT1509

Run the hardware test.
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1namylnAuthor Commented:
Isn't that the same test I spoke about in my original post or is this a different type of test?  Any idea if this video card is replaceable without having to replace the entire logic board?
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strungCommented:
Right. I missed that. Sorry.
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Davis McCarnOwnerCommented:
That iMac has an MXM ( http://www.mxm-upgrade.com/types.html ) video card which means it can be replaced; but, I need to know the part number of the iMac: http://support.apple.com/kb/HT1758
The x1600 cards is notorious for overheating and subsequently failing.  If you are lucky, we'll be able to upgrade it in the process.
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mmoore82Commented:
Run one of the many available stress testing applications, and stream an endless loop of youtube videos in a couple browser tabs  (endlessvideo.com).  

Based on the model and symptoms you describe, I concur with everyone else that you likely have a video card issue.  I've seen more video card issues in the 20" iMac than any other model.    I recommend getting the exact same card, rather than trying to upgrade to a different model.. it wouldn't help you much to eliminate one issue, but then get a kernel panic or something else. ;-)

Good luck
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1namylnAuthor Commented:
I'm not sure how to tell which version iMac 20" this is but I've pasted the more info about this Mac below.



  Model Name:      iMac
  Model Identifier:      iMac5,1
  Processor Name:      Intel Core 2 Duo
  Processor Speed:      2.16 GHz
  Number Of Processors:      1
  Total Number Of Cores:      2
  L2 Cache:      4 MB
  Memory:      3 GB
  Bus Speed:      667 MHz
  Boot ROM Version:      IM51.0090.B09
  SMC Version (system):      1.9f4
  Serial Number (system):      QP7010V4VUV
  Hardware UUID:      00000000-0000-1000-8000-0017F2CE229A

ATI Radeon X1600:

  Chipset Model:      ATY,RadeonX1600
  Type:      GPU
  Bus:      PCIe
  PCIe Lane Width:      x16
  VRAM (Total):      128 MB
  Vendor:      ATI (0x1002)
  Device ID:      0x71c5
  Revision ID:      0x0000
  ROM Revision:      113-xxxxxx-139
  EFI Driver Version:      01.00.139
  Displays:
iMac:
  Resolution:      1680 x 1050
  Pixel Depth:      32-Bit Color (ARGB8888)
  Main Display:      Yes
  Mirror:      Off
  Online:      Yes
  Built-In:      Yes
Display Connector:
  Status:      No Display Connected
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1namylnAuthor Commented:
I will try the endless stream.  I've tried looping dual and more 1080p within YouTube and have yet to be able to recreate this since I've had it in my shop.
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mmoore82Commented:
Sometimes it can take a while to reproduce.  

Type the serial number into this Apple site, and it will tell you what model you have:

https://selfsolve.apple.com/agreementWarrantyDynamic.do

Looks like a Late 2006, based on the information you pasted.
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Davis McCarnOwnerCommented:
You have a MA589LL/A or A1207 and it does not have an MXM video card :(
The systemboard part number is 661-4108 and the chaeapest I could find it was $370: http://www.ifixmaccomputers.com/661-4108-logic-board-128vram-20inch-2-16ghz-imac
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1namylnAuthor Commented:
I've recreated one of the issues.  I get a line in the video.  If I minimize the video the line isn't in the screen.  If I bring the video back up I can see the line again.  If I change the video to full screen the line goes away.  I've yet to get the machine to lock up fully.  Trying endlessvideo using high HD video.  Ran both xbench and novabench.  The system finishes the test with no issues I can see.
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1namylnAuthor Commented:
If I play a game like reversi, I can see the video from behind flicker occasionally through the game I'm playing.  It flashes very quickly.
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Davis McCarnOwnerCommented:
Ther isn't much you can do with bad hardware except to replace it!
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1namylnAuthor Commented:
Understood.  I was just trying to verify these issues were video card related.  In the past when I've experienced lines, dead pixels, etc. they stay on the screen.  This one is different so I was hesitating before coming to the conclusion the video was faulty.  This is only my 5th Mac repairing.
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1namylnAuthor Commented:
From what I'm reading this is common.  That being said, I don't think I can recommend replacing the logic board with good conscience as the new board may have the same issues at some point, correct?
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Davis McCarnOwnerCommented:
The user must be hypervigilant about keepin the cooling fans free from dust!  If you got very little out of your cleaning process; then, yup, it ain't worth repairing.  If it was quite dusty, then the replacement might be worth the cost.
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1namylnAuthor Commented:
Do you have an opinion about this program  http://www.macupdate.com/app/mac/23049/smcfancontrol and its ability to help my problem?
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Davis McCarnOwnerCommented:
It may delay the inevitable; but, you either have silicon which is damaged or a part which needs reballing.
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mmoore82Commented:
Late 2006 system might be worth $500 maximum if everything was working perfectly.  It's likely uneconomical to replace the logic board.. but  I would let the owner of the system make the call.  Like Davis said earlier, with bad hardware you just replace it most of the time.  If the damage has already been done, manipulating the fans will not help much.
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