Dual monitor freeze problem, possible causes

Over the past few weeks we have been investigating an issue affecting users that have dual display set-ups, most prominently when used in conjunction with the GeForce 4MX.

Typically when moving a window or another item between screens (but also under other circumstances in some cases), the system will freeze completely and will not respond to force quit commands or any other input.

MacFixIt reader David Kadavy writes: "I have a Dual 1 GHz Quicksilver 2002 G4 with 1.5 GB of RAM and an Nvidia GeForce video card. I have a 9x12 Wacom tablet, a logitech mouse and a Mac keyboard for input. My keyboard and Wacom tablet are plugged into the USB ports on the back of my machine, and my mouse is hooked up into a port on my keyboard. I have a dual monitor configuration.

"I have found that if I have my mouse plugged into my keyboard, when I am moving a window from one monitor to the other, I will ocassional experience a freeze: the mouse cursor will disappear, nothing on the screen will change, iTunes will continue producing sound, and there will be no response [...] I have found that removing my mouse from my keyboard (and only having the keyboard and wacom tablet plugged in) eliminates this issue."

So it appears that some part of USB device communication is causing a problem in dual monitor configurations. It is as of yet unclear whether this problem will require a hardware fix from NVidia, or a software revision from Apple.

In the interim, however, users may want to experiment with the addition of a PCI USB card for keyboard/mouse connectivity.

If you have any other suggestions, or are experiencing this problem, please drop us a line at late-breakers@macfixit.com.

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