[Salty]

Reset the PRAM. I was just about ready to kill my MacBook, I hadn't really connected it to my desk monitor since getting the release version of Lion, and suddenly my monitor kept flickering and then the computer wouldn't recognize it. I did some googling and found out that resetting the PRAM might fix it, sure enough it did. Hold down command, option, P and R when you restart and you're set

[MacNNUK]

I had the same flicker problem with my iMac 17" 2.0ghz Intel Core 2 Duo 2007 vintage.

Snow Leopard.

Soon after updating to 10.6.8 from 10.6.3 (may be connected ?)

4 years old refurbished, no other problems to date.

Researched service availability and costs & buying a new iMac.

Rang Apple Sales UK, they gave me Apple Service UK phone number, they talked me through the PRAM Reset procedure.

(Unplug all cables inc power, hold down power button 10 seconds, reconnect all cables, then 4 keys as above)
(Actually 3 keys, then P as soon as I pressed power)

Flicker cured, thank you Apple, no charge, no service required, and no new iMac cost, yet !!

I did receive a quote from a UK service company (non Apple)
£35 to look at my iMac
£110 if it was a "driver" fault
£520 to replace the LCD screen !!

[MacNNUK]

Six months later, the same flickering arose, did a PRAM reset, which cured it, again.


However, after coming out of standby since resetting PRAM, entering data into an Excel cell, the screen around the cell went haywire, then a few seconds later the whole screen went haywire.

I rebooted, strange vertical images,

Reset PRAM again, here I am, everything OK, for the moment.

This is what my screen looked like just after entering data into Excel.



Any ideas, is my iMac on it's way out ?

( I tried a screen grab when whole screen went, didn't capture anything.)


....

[reader50]

Screen corruption is most commonly a GPU problem. Though it can be VRAM or bad caps around the GPU.

If the problem continues to come up, I would suspect a hardware issue. Software shouldn't do that, especially with a built-in screen. The drivers for OEM parts should be bullet-proof.

It's interesting the corruption only affects certain window contents, but not the scroll bars. Like a single graphics layer is affected.

[MacNNUK]

That was quick, thanks.

I've noticed in the past that after entering data in an Excel cell, very occasionally, I get small vertical lines like jumbled data, which clears if I click on another cell.

It's probably nothing to do with Excel, either tonight or previously, just happens to be the first entry I did after coming out of standby.

[MacNNUK]

OK, I've bitten the bullet.

Had to reboot twice more this morning, screen disturbance and iMac freezing up.

Strangely, it's been OK for hours now, with some standby's.

I see the screen disturbances as a warning sign, the iMac I use, in my sig, was Apple reconditioned and is now 4½ years old.

So, just bought an iMac MC309B/A Desktop Computer, Intel Core i5, 2.5GHz, 4GB RAM, 500GB with 21.5 Inch Monitor for £999, with a 2 years free warranty from John Lewis UK.

They have a good reputation, and give 2 year warranties on most electronic items.

I took the plunge now, otherwise it's a bit like decorating just to sell a house, you don't get the benefit.

Just a thought, is the extra memory I installed in my current iMac compatible with my new one ?

This is
1GB, 200-pin SODIMM Upgrade for a Apple iMac 2.0GHz Intel Core 2 Duo (17-inch) System
2GB, 200-pin SODIMM Upgrade for a Apple iMac 2.0GHz Intel Core 2 Duo (17-inch) System

Does migration actually work that well ?

[Waragainstsleep]

Your RAM will not work, sorry.

Migration is fine most of the time. My current MBP install is a hangover from an iBook I think. Via at least one other MBP and possibly a MacBook too.

[MacNNUK]

I've just had a thought !!

I have an iMac to HDMI adaptor, which works very well, bought it as backup.

Apple Mini-DVI to HDMI (female) Adapter Cable for Apple Mac

If my screen display goes wonkey again, I'll try the iMac to HDMI feed !

However, if it's a board fault, presumably the fault will also show on my TV with HDMI input also.

I'll plug it in now. Shows at 1080p when mirroring, 1080i also available from display menu.

Probably won't help the freezing though.

[MacNNUK]

I did an Extended Hardware Test overnight, No Problems found !

[ibook_steve]

Originally Posted by MacNNUK 

I did an Extended Hardware Test overnight, No Problems found !

Unfortunately, based on your screenshot, I don't think that test is conclusive. That is definite GPU/VRAM corruption.

Steve

[MacNNUK]

Thanks, you know a lot more than I do !

Can I correct GPU/VRAM corruption ?

[OreoCookie]

No, you can only replace the graphics card (I think the graphics card is on a separate daughter card in iMacs). Otherwise, the main board needs to be replaced. Sorry, dude.

[MacNNUK]

That's what I expected, it seems to be crashing more than display corruption at the moment, Yusa seems to have done a good job.

My new iMac is due in a few days anyway.

Thanks all.

[MacNNUK]

Originally Posted by MacNNUK 

I have an iMac to HDMI adaptor, which works very well, bought it as backup.

If my screen display goes wonkey again, I'll try the iMac to HDMI feed !

However, if it's a board fault, presumably the fault will also show on my TV with HDMI input also.

I'll plug it in now. Shows at 1080p when mirroring, 1080i also available from display menu.

As I thought, the TV (Via HDMI) shows exactly the same iMac screen when the fault occurs.