1st series iMac G5: Booting problems, kernel panics, waking from sleep...

Question

Specifications of the iMac described: 1.8 Ghz, 1GB, 80GB, 64 Mb Nvidia VRAM, Airport, 10.5.5
Back in August 2004 my dad bought us kids an iMac G5 for ‘family use’. It had a fresh install of 10.3.5 on it and compared to the (1999) iMac G3 it replaced it was amazingly fast.
The iMac never showed any signs of probable issues, until we decided to upgrade to Leopard in January 2008. Initially, this upgrade was only meant to be able to sync with the latest iPod nano (who demanded a newer version of iTunes).
After the installation the first thing I noticed was a high CPU usage, the machine seemed slower than ever and that with 1 Gb of RAM (the minimum sys. req. for Leopard are 512 Mb of RAM). Anyway, then the real thing started, it wouldn’t turn on anymore. We brought it to an Authorized Apple Reseller, the Tech department said the Logic board had failed. The costs of the fix weren’t the worth the computer anymore, so...end of story. The iMac was indeed one of the bad series, although it hadn’t any swollen capacitors.
My dad already made up his mind and bought himself a Macbook. He then told me that if I was able to get the broken iMac fixed, I could keep it. And so, I bought an ‘as-is’ logic board on Ebay. Last weekend I installed it, and it actually seemed to work! Yet, the problems are during the startup: the first thing I see is a screen full with horizontal lines flickering all the time, like an old TV with bad signal. Mostly it won’t boot and I get the message to restart the computer (kernel panic, I got dozens of logs already!). Sometimes it got stuck during booting (grey apple screen with gear in the middle) making the fans go crazy (after a while) and sounding what others describe as a ‘jetliner taking off’ sound. Sometimes the screen remains black. Generally it takes me 5 to 10 minutes to start up properly. Maybe it’s just me but it seems like when the computer has warmed up a little (by turning on and off on and on) starting up gets smoother. I mean the startup screen suffers from less horizontal flickering lines.
During the use of Leopard, I again get high CPU usage, especially when I use multiple programs at the same time, or when starting multiple programs. My iStat Pro said once that the fans were running at 4700 rpm and the heat of the CPU was about 70 Celsius. If I really want to **** my iMac off I should play a racing game. That just totally freaks him out! These problems could probably be solved by adding more RAM. Right?
The iMac also has a sleep problem. Sometimes after lets say an hour or so, you can’t get it out of sleep mode (by manipulating keyboard and/or mouse, the sleep light stops, but the screen stays off --> only solution is to restart). What happened to me once was that it slept so long that it just got into a deep sleep by turning itself off completely!
Here’s a list of what I tried so far:
- Disk Utility: Resetting the permissions, no problems were found.
- Resetting the SMU, both on the logic board itself as by pressing the power button 5 - 8 seconds, no improvements.
- Resetting the PRAM, no improvements.
- Did the Hardware test of the original install CD, nothing was found, all good.
- Did Archive and Instal, this actually messed my system entirely, cause it wouldn't boot at all and when starting up from the Leopard installation DVD it wouldn't recognize the Macintosh HD.
- Did Archive and Instal with the original disks, this disk did recognize Macintosh HD and so I installed the original system, 10.3. Booting problems and those flickering lines are still there though.
Next phase will be erase and install, but first I want to know what you guys think about all this.
Oh eh, One more thing; The guys at Applecare (phone support) told me that the replaced logic board was also out of warranty and so they couldn’t help me. But as the man on the phone was kind, he told me to go look for a special ‘driver’ on the net. He said that the driver should be able to resolve some of the issues described. He said that I had to give in the name of the LB on google and look for results. Is this bogus? Because I haven’t found anything useful on google so far. What’s the name (rather than a number) of the LB in the first place?
I hope you guys can give me some answers. I'm kinda desperate. But I still feel there's hope...

Answer 1

The symptoms of a flakey power supply are sleep problems and you have done all the right things as far as resetting the SMU and PRAM. Your CPU usage can be tracked by going to Utilities>Activity Monitor - look and see what is hogging the memory. The flickering lines could also be an optical system going south.
The other thing you can do is run DiskWarrior or TechToolPro to see if you have corrupted directories. Preferential Treatment will let you check for corrupted preferences.