Imac 27" graphic problems

[senseless]

Hi, my Imac 27" with external monitor has a weird graphic problem. On restart, it will randomly flash lines across the screen but this problem goes away after a few days of being left on. Once the problem stops, it's ok until restart.

It doesn't seem to be a heat or vibration issue, but why does it only happen on a fresh (re)start? The temps don't change in this case. Could it possibly be a Snow Leopard software issue? The monitor is ok with another source.

 

[Detrius]

Sooo... it's the external monitor with the lines? Are they always in the same location on the screen itself? What happens if you change resolution? Can you post a picture?

Btw, I suspect it's a bad LCD and that you will see the lines from another source.

 

[senseless]

I'm using an external because I broke the internal display connector. The monitor is ok, because I can switch sources and the problem disappears. The lines are about 1" high and momentarily flash and cause the screen image to jump. I've had the computer on for 3 days and it's fine, but as soon as I do a restart, it's back again. Very strange and surely caused by the motherboard damage initially. Changing resolutions does nothing.

 

[Detrius]

Changing resolution must do something. If the issue stays in exactly the same place on the physical LCD, then it's going to be the LCD, despite your assertions that it doesn't happen on another machine. The actual liquid crystal array know nothing of resolution.

 

[senseless]

I should say that changing resolutions does not cure the problem. The flash and jitter is all over the screen, but mostly the bottom half. If I change the monitor A/B source to another mac, then the screen is rock steady and fine.

Moving the mouse pointer or scrolling the screen makes the issue much worse.

 

[senseless]

Interesting update: Problem occurs after every restart, but goes away after waking from a few seconds of sleep. This is consistent and very baffling.

 

[panzer06]

Hmmm, sounds like the problem could be related to heat and expansion. Perhaps some connector related to the display outport is loose and letting it warm up expands something and creates a better connection. Just seems like it wouldn't take "a few days" to warm up enough for that to be the issue.

...Or maybe you fed one of those creatures after midnight.

Cheers,

 

[Detrius]

Moving the mouse pointer or scrolling the screen makes the issue much worse.

Take a screen shot (shift-command-3). If it's in the file that's created, then the issue is in your graphics memory and therefore not anything from your video port out.

If it's not in the screen shot, then at least the processing is being done correctly.

I could tell you really quickly with just a photo.

 

[senseless]

These were captured with a video camera. I tried to get a still cam or a screen capture, but couldn't do it. Sometimes the screen blacks out completely, for a split second.