Problems with RAM upgrade iMac G5 1.8GHz

Question

Stuck - Need Help!
I've previously upgraded up iMac to 2 500Mb RAMs and felt recently that it needed that little bit extra, so I ordered two 1Gb chips from crucial.
Followed instructions to T, but with the two new chips in, the machine won't load.
Interestingly, it boots up with the following RAM combinations
old 500MB + new 1GB (in any combination) - recognised as 1.5GB
one new 1GB RAM (again either one) - recognised as 1GB
I spoke to crucial who said that as the RAMs work individually, there isn't a problem with them, it could be a Firmware issue. I've upgraded all my software, and don't know what to do next?
Anyone overcome a similar problem in the past?
Thanks

Answer 1

I'm experiencing something very similar to shaow. I'll share my experience in gory details - sorry for the long post but I've spent more hours trying to stabilize. I should have worked the hours at walmart and bought a new iMac with the money I could have earned
Anyway, here goes:
Two iMac G5 1.8Ghz 17" (both Fall 2005 model), will call one A and the other B.
Prior to attempting ram upgrade: A, config working fine: both a config using 1GB slot 1, 256MB slot 2 and a single 1 PC3200 1GB stick. OS X 10.4-10.5.7. No problems. I did have the motherboard replaced under warranty after having sleep problems - capacitors were expanded. No problems since that motherboard swap.
Prior to attempting ram upgrade: B, config working fine: 2 x 256MB sticks. OS X 10.3.9
Ordered 3 PC3200 400Mhz 1GB sticks from Data Memory Systems.
Upgraded A: Added 1GB stick = 2GB total
Upgraded B: Removed both 256MB sticks from B and added two 1GB sticks = 2GB total
Booted B, experienced gray screen of death with the multi-language crash message - somethign like: 'Please hold down the power button and restart'. Power cycled B, booted off a retail box DVD of OS X 10.5.6. Began upgrade to 10.5.6. Gray screen of death part way thru upgrade. Power cycled, gray screen of death again during early boot phase.
Decided to run tests on B. I could not locate the Apple Hardware Test (neither on system dvd 1 nor on a separate DVD). I resorted to using TechnoTools Deluxe which was included with AppleCare box. No hardware problems found including on the 2GB memory.
Removed both new 1GB sticks, pulled older working 1GB stick from A and installed into B. Completed upgrade with just 1GB memory on B to 10.5.6 and subsequently pulled down all updates for OS X 10.5.8. Powered down, added second 1GB stick to B, booted into 10.5.8 successfully. Repaired disk permissions, restarted. Began using applications, then after only about 5 minutes experienced gray screen of death. Powered down, removed new 1GB stick, replaced with one of the two remaining new 1GB sticks. Read about reseting PRAM/NVRAM. Followed steps to reset PRAM then decided to do the reset NVRAM within openfirmware. Started back up and logged into 10.5.8. Ran several applications - did not experience gray screen of death after about 20 minutes use. Have not had time for further tests on B yet.
Back to my saga with A (my original iMac G5 that was working fine with 1GB stick on 10.5.7):
Called Data Memory Systems and they sent me a replacement for the 'bad' 1GB stick.
While I was waiting for the new 1GB stick from DMS, I was struggling to get machine fully updated. Software Updater was failing with the weird network error (network was fine) and after following steps to troubleshoot, I backed up the user accounts and decided to reinstall OS X fresh from the 10.5.6 retail box (family license). Finally, I had OS X 10.5.8 all fully updated on the 1GB iMac G5 (A).
New memory arrived, installed 2nd 1GB stick. Booted up, immediately I got the gray screen of death. Restarted, booted up got about 5-15 minutes use then gray screen of death. Puzzled, I called DMS who said unlikely I got 2 bad sticks. They suggested I try memtest. So I did...
So on A, I first ran memtest from single user mode on the 2GB config. It crashed immediately with some 'Unexpected' error. Did not look like a memory error. I powered down, removed 2nd 1GB stick, and ran memtest from single user on the 1GB stick. Ran all tests 3x over a couple hours - no problems found. Retested after swapping the 1GB stick for the other. Both tested fine. Installed both sticks again and ran memtest all tests, one pass (didn't want another 6 hours lost) on the 2GB config, and all tests passed. Booted up and got gray screen of death - I don't recall if it was on bootup or after running but I ran fsck with no disk problems found, then restarted, logged in, ran disk utility to repair all permissions. Some repairs were made. Restarted A, reset PRAM and NVRAM again, booted successfully.
I haven't had much time to run extensively apps on A yet. It's sleeping as I type this on another mac. My next test will be to reset SMU.
I'm starting to wonder if the original iMac G5 has firmware problems that would prevent it from being unstable with two 1GB sticks??? My experience on two identical models of iMac G5 plus reading this post with VERY similar behaviors and after all the normal tests. I've concluded the memory is A-OK and something more sinister is lurking...
Any thoughts are appreciated.