IMac G5 – Won't startup except in Safe Mode (10.5.5). Otherwise Blue Screen

Question

I’ve had my iMac (pre-iSight) for about 3 years now and up until recently never had any major problems with it, despite using it for about 12 hours per day, every day.. A couple of minor problems however had developed, but several months ago and didn’t seem to affect the system:
(1) Software update stopped working (had to download & install updates manually) &
(2) Couldn’t verify or repair permissions (even pre 10.5.5. Even when I tried to repair them from another startup disk, the message I got was ‘no package receipts’ – although I could see that they were there in the “receipts” library folder)
A couple of days ago I decided to try and fix the problems by erasing my startup disk (after backing up all my data of course) and re-installing 10.5 from the installation DVD and then bringing the system up to date. At the time I did this I hadn’t upgraded or installed any new software for several weeks.
For about one day after that it worked fine. The only ‘alarming’ thing that I noticed during that day was that whilst playing a movie the CPU temperature rose to about 89 C. (I use Temperature Monitor). I read somewhere that the CPU temperature should not exceed 85 for this model and that if it did the system would either shutdown or go to sleep, so I was surprised to see it go as high as 89 (assuming that the right temperature was being reported) before it went to sleep. However, even after that it, it started up correctly a couple of times.
Since then it will only boot in Safe mode, and when it does it carries on working indefinitely without any problems. The only thing that I lose in safe mode which seems odd – in addition to all the things that I know I should lose – is Audio. The preferences panel says: no input, output devices attached (ie not even the ones built-in).
If I try a normal start up, the system will go through the grey screen, apple logo, spinning ‘cog’ etc and then almost always go to a blue screen where it stays put. There is a black cursor in the top left corner which, when I try to move it, duplicates itself so that I end up with 2 cursors – one which moves and one which stays in the top left corner.
On very rare occasions (about 1 time in 20) during a normal startup the system will get past the blue screen and to my desktop (in fact this happened several times consecutively before I got to the point where I could only startup in Safe Mode). However, moving the cursor into the menu bar or into the dock would result in the whole screen freezing – the cursor would move, but nothing else would happen). Also I would see that several pixels were ‘missing’ from the desktop. The desktop is normally solid green, but I would see 3 or 4 red and black pixels.
I’ve studied all the forum topics that even remotely resemble my problem and tried just about everything I can think of including:
1. Resetting SMU & PRAM (repetitively)
2. Running the Apple Hardware Test – All tests passed
3. Replacing the PRAM battery
4. Check that the fans are working (I can hear them and when I take the back off, both fans spin)
5. Erased the disk again, installed the OS from the installation DVD, so that there is no third party software on the system. (and then tried a normal boot both with the original 10.5.1 and 10.5.5 after applying the combo update).
6. I have several external disks with several copies of the OS on various partitions, including a 10.4.11, but trying to boot from any of those ends with the same result. I can only boot in safe mode, other wise I get a blue screen (or very rarely it will squeak through to the desktop & then immediately freeze).
Always the same result – safe boot only.
From reading through the various topics, I get the feeling that my problem may be related to the graphics card, but if that is the case I don’t understand why the system will always boot in safe mode and then run without any problems all day. It even allows me to play movies: very jerky (and no sound), both when I move the QT window and the images themselves, but it still plays.
Any thoughts on what the problem might be (other than fatal) would be greatly appreciated. Or an explanation why, if it is the graphics card, the system will continue working after safe boot.
I’ve copied out the system details from Profiler that I think are relevant below.
All the ‘x’’s in the the ROM revision for the ATI Radeon card look a little odd – never seen that before and I don’t know how long its been there.
Model Name: iMac G5
Model Identifier: PowerMac8,2
Processor Name: PowerPC G5 (3.0)
Processor Speed: 2 GHz
Number Of CPUs: 1
L2 Cache (per CPU): 512 KB
Memory: 1 GB
Bus Speed: 667 MHz
Boot ROM Version: 5.2.5f1
Serial Number: W8539……
ATI Radeon 9600:
Chipset Model: ATY,RV351
Type: Display
Bus: AGP
Slot: AGP
VRAM (Total): 128 MB
Vendor: ATI (0x1002)
Device ID: 0x4150
Revision ID: 0x0000
ROM Revision: 113-xxxxx-117
Displays:
iMac:
Display Type: LCD
Resolution: 1440 x 900
Depth: 32-bit Color
Built-In: Yes
Core Image: Software
Main Display: Yes
Mirror: Off
Online: Yes
Quartz Extreme: Not Supported
Display Connector:
Status: No display connected
Many thanks for your help

Answer 1

I had a very similar problem with my 20" iMac G5 ALS running 10.4.11. It began with random freezing inside the OS and intermittent slow booting, but quickly progressed (over a matter of days) to hanging at the blue screen before the logon window, just as you described.
I too, found that booting in Safe Mode was successful. I ruled out the airport card by manually installing that kernel extension in Safe Mode. A check of the logs pointed to "ATY" which I've since found out is a reference to the ATI drivers, which brought me to this post.
At least on my system--and I have tested this on Tiger (10.4 and 10.4.11) and Leopard (10.5 and 10.5.6), the only .kext that needs to be removed / renamed is ATIRadeon9700.kext. My preferred method of doing this is to drop to the terminal and type:
sudo mv /System/Library/Extensions/ATIRadeon.kext /System/Library/Extensions/ATIRadeon.kext.disabled
This preserves the relevant permissions and ownership, which you'd otherwise have to reset manually if you copy the file elsewhere and then delete the original in the Finder, and then want to restore it to its original condition, BTW:
sudo chmod -R 755 /System/Library/Extensions/ATIRadeon.kext
sudo chown -R 0:0 /System/Library/Extensions/ATIRadeon.kext
Any OS X update will replenish the file, so you should be at the ready to reboot into Safe Mode the first time and rename the file again.
The downside to all this is that the video acceleration doesn't work, so graphics operations are slow and jerky, but at least everything else seems to be okay, in my case anyway.
Popping open the case did indeed reveal four bulging capacitors. I bit the bullet and purchased some replacements, part number 647-UHN0J182MPD from Mouser:
http://mouser.com/Search/ProductDetail.aspx?qs=pjJ%252bhmlZec6zHXGt6EoiHw%3d%3d
Although I wasn't looking forward to desoldering my logic board, I wasn't real hopeful that I'd have success getting the local Apple shop to replace it under warranty either. I did find some helpful information on performing the fix yourself:
http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php
And I do want to be able to sell this thing for at least a little cash to help offset the cost of a new quad-core iMac, whenever they're released.
Fortunately, for me, the service tech at the Genius Bar at the local Apple store agreed to fix it under the power and video extended warranty, even though it was slightly outside of the warranty period, due to the fact that I had brought it in about a year ago and had the power supply replaced under the same warranty.
I almost didn't bother to bring the machine in because it's a real nasty day here today, and I figured they'd just tell me "That'll be $800 to fix it," and I'd end up doing surgery on the logic board anyway in addition to carrying the thing up and down the steps to my condo. Boy am I glad I did, though. Apple customer service rocks.