Desktop iMac A1224 - help diagnosing video issues

[hroldan]

Hi, this 20 inch 2009 iMac - Intel Core 2 Duo with NVIDIA GeForce 9400 254MB is having this video issue (picture below). Everything works except the video to screen. However, when connected to an external video output the image appears perfectly clear and sharp.

Is there a way to diagnose what's going on?

The usual suspects:

1. The LCD screen
2. The LVDS cable
3. Loose contacts/connections around #1 and #2
4. The graphic card soldering, damage due to overheating, etc.
5. Any blown capacitors?

This is confusing:

• I've been reading a lot, but the comments and information is a bit contradicting. Some say as long as the video output to an external monitor works, it's not a graphic card/gpu issue, and so, it must be an LCD or LVDS cable issue. Others say the external video test working fine is no proof of the graphic card being ok.
• Found a video about a similar issue (can't remember the iMac model) explaining the problem went away installing Windows, as there is some issue with the Mac graphic drivers and I think firmware, but the computer worked perfectly fine as long as he stayed using Windows. I thought this was funny and nonsense, but surprisingly enough I found other people confirming this (I haven't tried using Windows here), I would be fine moving to Windows on this iMac.

Oh the irony!!!!! I enjoy watching random repair videos, and by chance... 2 years ago came across one guy having this exact issue; his iMac on the Youtube video looked EXACTLY like this, same video distortion, but because it was a random video on a random set: I can't remember the details, I think it was a blown capacitor somewhere (?) but I'm not sure, that's the problem of watching random videos in sets because later the details end up as mixed memories. I've been trying hard to find that video with no luck.

Here is how the video appears on screen, running El Capitan.

Any suggestion will be appreciated.

 

[MacsBug]

Have you tried to boot into Safe Mode or into the Recovery HD to see if the problem persists?

 

[hroldan]

Have you tried to boot into Safe Mode or into the Recovery HD to see if the problem persists?

Thanks, so far no luck. It seems to be a hardware issue, but not clear what kind.