A year ago when I first noticed a green dot had appeared on my PowerMac G5's display I was a bit disappointed, but not fully surprised because LCD pixels are known to die, go dim, or get stuck in a specific color. Not thinking much of it I dismissed it as a common issue and continued to use my computer; however, these dots were going to soon become a larger problem for me.
A short while after noticing this dot, another one appeared and I became concerned that the display was not working properly. To test this, I shut off the display and turned it back on, but the dots remained in place. My display is a 24" widescreen monitor from BenQ and when powered up it shows a "BenQ" welcoming logo with a full-screen purple background. The pixels seemed fine when this screen was shown, so I hoped the problem was fixed by a quick screen reset; however, when the desktop reappeared the green pixels were still there.
This ruled out the display hardware as a possibility, so I decided to test the problem a little further by outlining exactly how the pixels behaved.
When they appeared they seemed to be stuck with the image they were on, so if I moved an image around on the display the dots would stay with it, but if I zoomed in on the image the green pixels would also get larger, indicating they were rendered with the current image.
My other observations:
They did not appear when the computer was just turned on after being off for a while.
They showed up more rapidly on hot days (100°F in the summers here) and rarely showed up in winter (average temperature is 50-60°F).
Graphically intensive tasks (games, image and movie manipulations) caused them to show up more rapidly.
Reloading the rendered image, or otherwise performing a manipulation on it, would cause the distribution of the green pixels to change.
No apparent pattern to the dots.
No apparent slow-downs in performance.
There was clearly something wrong with the way images were being processed, and I suspected it was either in some frame buffer or other component of the GPU. Over time the problem seemed to get worse, but it would still only happen after the computer had been used for a certain amount of time, and especially if games were recently played.
Initially I was not worried about the issue, and figured I would just monitor it since over the past year the problem would come and go. However, finally during this past weekend the issue went out of control and green pixels began flooding the screen. This would happen even after running the system for only 5 minutes after a cold boot.
Since this had been a long-standing issue and I knew it was not a problem with the display, my first step in troubleshooting was to test the software to see if a driver problem could have been causing the artifacts. The video card in this computer is a third-party Radeon X800XT, and while this card is supported in OS X, being a third-party solution could mean a driver incompatibility may be an issue at hand.
The easiest way to test the driver is to reboot the system into Safe Mode so drivers are disabled, and also to boot to an alternative volume such as the OS X installation DVD or a third-party diagnostics DVD; however, upon doing this the problems remained. Furthermore, just like when running the installed OS these artifacts did not show up if this was done on a cold boot.
The only other options to me at this point were firmware settings and other hardware-related issues that could have cropped up over time. With the card being an older AGP-based card I could not try a different slot for it. Nevertheless I removed the card, cleaned it and the slot with a blower, and ensured it was seated and secured properly without any components touching the metal chassis (the plate separating the G5 CPU coolers from the expansion slots is very close to the graphics card).
I also tried a PMU reset (called SMC on modern systems) and a PRAM reset (the only viable firmware resetting options), but these along with the cleaning did not work.
Puzzled at this point, I was concerned that the hardware was going bad, especially since besides buying used ones on eBay, higher performing graphics cards for these systems are relatively hard to find.
This made me think about the situation a little more, and I realized that during the same timeframe when the pixels appeared I was aware of some odd fan sounds in my system. When the system would start up or wake from sleep an audible grinding whirr sound would appear for a minute or two before going away.
This sound had been with the system for a while and I did not give it much attention. It seemed to come from the front of the computer, so I figured dust had built up on one of the chassis fans, throwing it off balance and causing the rattling. It was odd the sound would disappear after a minute or two, but but since everything seemed to be working just fine I had not investigated it further, and in fact got used to its occurrence. Despite this I decided to clear up this problem with a thorough cleaning of the system.
Using canned air, I puffed around the fans (thankfully the holes and large side door on Apple's pro systems makes this very easy to do) and copious amounts of dust came off the thing. I was hopeful because this could have been causing both problems I was experiencing. Not only can dust can build up on fans and make them noisy, it can also reduce their overall speed making them work harder, and build up on heat sink systems and reduce the cooling efficiency of the computer (there was a lot of dust on the GPU, potentially causing it to overheat).
With my fingers crossed and my system now nicely clean of dust build-up, I booted it up again and this time the grinding sound still appeared but was much shorter in duration. The system seemed to be fine so I got to work and almost immediately upon launching the first program the pixels appeared again and this time the problem was disastrous: there was basically a field of green pixels across the display that would not go away.
Hoping the massive prevalence of the glitch was because of a faulty setting, I shut down the system and let it stay for about ten minutes, and then booted it up again. The pixels were initially gone, but rapidly came back after a few minutes, making the system unusable and confirming the problem had become much worse.
Other hardware issues
Luckily the G5 has a clear plastic covering inside the chassis door that allows you to view the components, and already having the main door off I noticed the GPU fan was spinning very slowly and the grinding noise was very apparent. When I saw this I nearly smacked myself for not investigating this earlier and quickly shut down the system. I unscrewed the mounting bolt and removed the card, and nearly burned myself by just touching the edges of the card. It was so hot the plastic housing of the heat sink had cracked a little, and I could not hold it for long without fear of injury.
So my fan on the GPU was the problem. It's ironic how a small $5 fan can be the downfall of a system that originally cost over $3500.
Spinning it manually made the same grinding sound as before and there was definite resistance to the movement (there should be minimal noticeable resistance to computer fan movement when spun manually--at most a few minor "soft" detent-like bumps where magnets align).
Computer fans are many times cheaply made and while they should last a long time, they use porous metals and other materials in the bearing that over time will wick away the lubrication and cause the bearing to bind and then release. This leads to the rattling that can be heard. I looked up the part number and ordered a replacement fan on eBay; however, it will take several weeks to get here (all the small important parts seem to come from China).
Needing the computer running I decided to repair the fan myself. Provided nothing else was physically damaged I could get this one up and running ASAP with a drop of oil to re-lubricate the fan. On many GPUs, removing the fan is not always possible without also removing the heat sink; however, on the X800XT card the fan is very accessible and can be removed by unscrewing four mounting screws that are right under the fan blades.
I took off the fan and unplugged the power cord (which snakes under the heat sink) and revealed the back of the fan which has a sticker with specifications on it. Removing this sticker reveals the fan's bearing, and I dropped a single drop of lightweight oil onto it. For a more in-depth look at this procedure for similar fans, see this TechRepublic article.
I spun the fan manually to work the oil into the bearing, and after a few spins found the grinding when I manually spun the fan had disappeared. Relieved, I reattached the fan and screwed it back in place, and installed the GPU back in my system. I booted the system with my fingers crossed and everything worked great. The fan is spinning rapidly, and there are no grinding noises at all. More importantly the graphical artifacts are now gone, and have not returned even after taxing the GPU by running several graphically-intensive games for about 15 minutes.
Propping the side door open I felt the GPU's heat sink, and found it was warm as expected, but not blistering hot. For now the disaster is averted and the fan should do its job; however, I'm still wary of the fan and plan on replacing it with the new one when it arrives.
Note: Only try manual fixes like this if your computer is no longer covered under warranty, and only if you feel comfortable working with the components of your system. The computer boards are resilient to heat, but can be easily damaged by a slip of a screwdriver or shock from static electricity buildup.