IMac freezes during games

Question

Hi,
I am knowledgable about Macs (used them since '84 and Apple II before that) - well, I was enjoying another insomniac session with the excellent Redline racing game when suddenly the machine locks up. Freezes, completely. I didn't get the kernal panic screen... just a still image of my current car skidding around some corner... frozen solid. Command-Option-ESC does nothing... I couldn't see what was happening but hoped I could Force Quit somehow. I needed to do a hard restart.
This happened several more times after rebooting each time. The machine would lock up after about 5 or 10 minutes of play. So, I reset the SMU... no luck. So, I reset the PRAM. No luck. Then, I reset the NVRAM (open firmware)...still no luck. I wrote to Ambrosia and asked for support figuring it was Redline. No luck.... The problem showed up while playing another game as well (Star Wars Battlefront)...
Long story short... after taking it to my local Apple Store (no luck there) and doing a clean reinstall of Tiger (still no luck)...
After a few minutes of playing any graphics-intensive games my iMac locks up.
Oh, and I used the hardware test that came with the iMac... all systems checked out normally... logic board, RAM, everything.
Thanks,
Jon W. Barto
PS - No new hardware added recently. Games ran fine until this past month... machine is 1 and 1/2 years old. Not an extended warranty issue... it's a revB iMac.
PPS - Follow up to my own post: This morning I removed one of the two 512 MB RAM modules and was able to play my Star Wars game for about 4 levels... 2 to 3 times longer than before. It still froze however, but after a long while. My friend who is one of those alpha-geeks told me that it may have been because most of the RAM was allocated to the OS while the game was running off the hard drive (virtual memory). This makes sense. I am running Rember on the installed RAM right now (the Apple RAM that came with the iMac) to see if it really is defective. Then I am going to install my 3rd party RAM by itself and see if it locks up with just that installed.
I'll let everyone know how it goes.
Still, any advice would be helpful if I am missing something. Thanks.

Answer 1

Hi, Jon W. Barto
just two remarks:
a) the hardware test of apple does not find all
problems; it frequently tests hardware good, which
isn't. so it is ok, if it tells you about a hardware
problem, but it might be not ok, if everything tests
fine.
b) you are certainly aware that you can check the
memory use with the system monitor. thsi might help
you to identify whether you freezing problems are
caused by a shortage in RAM.
My iMac was running with 1 GB of RAM... I don't think there was a shortage. Also, I cannot use System Monitor (you mean Activity Monitor) while I am playing a game.
c) (I apparently cannot count: a, b, c is more than
2)
could it be a logic board problem? How old is your
iMac? you are certainly aware as a long user of macs,
that the iMac G5 had some bad batches, and there is
an extended garantee, if you machine falls into these
batches. check the Apple pages for mor info about
this.
Mine is a rev B iMac... my RMS (I think that's what it's called) did fall under the Power Supply extended warranty agreement, but it is not a power supply issue. The lady at the Apple Store said that it might be the logic board also.
please, report back with the outcome.
Thomas
BTW, does anyone know if replacing the logic board will solve the problem permanently, or is it a temp. solution until it craps out again?
iMac G5 2Ghz 1 GB RAM, iBook 600, 3G iPod   Mac OS X (10.4.8)   250 GB LaCie FW HD
iMac G5 2Ghz 1 GB RAM, iBook 600, 3G iPod   Mac OS X (10.4.8)   250 GB LaCie FW HD