Special Report: Troubleshooting the Power Mac G5

CNET staff

Sept. 2, 2009 10:36 p.m. PT

16 min read

Covering these and other issues:

Working with Optical audio out There is an issue with the optical-out jack on the Power Mac G5 where short sounds don't appear to get passed though the optical connection, but longer ones do. A MacFixIt reader notes that this may simply be a drawback of certain optical outputs:

"The sound dropout seems to be a drawback of the way optical links send data -- the exact same thing happens at the begining of a track on a CD being played with my Laserdisc player or DVD player, or at the layer break (when the audio stream breaks as well) on a DVD... The only way around this in the case of a computer would be to constantly send some data so the amp always sees an incoming signal to process. iTunes seems to do this, and maybe someone will come up with an app that plays silence (keeps the auiod output awake, really) to prevent this from happening."

We should note that this doesn't happen on all computers with optical audio outputs, so perhaps some sound cards handle this situation more gracefully than others (and than the G5's optical-out circuitry).

The G5's volume control doesn't affect the optical output; this is normal behavior for digital audio output, as the data is generally being sent to an external DAC (digital-to-analog converter) for processing, and volume is controlled by the receiver or amplifier that is fed the analog signal. In this respect, an optical digital output is similar to a standard line-level output. William Kucharski offers a technical explanation behind some of the optical audio out quirks we have been covering over the past week:

"Basically, most any D/A converter needs a few samples to lock onto the proper sampling rate and format for the data. For example, most speaker systems and D/A converters can handle PCM, Dolby Digital or DTS data streams at at least 44.1 and 48KHz.

"It usually takes a few samples for the converter to recognize the format and sampling rate it is receiving, with the end result that playback cannot occur until the converter has its first full frame for the audio format being transmitted.

"If the device sending the digital audio does not maintain a digital data stream at all times - regardless of whether audio is currently being sent or not - the D/A converter will have to go through the format detect cycle all over again.

"As you state, the ways to avoid this are either to have the digital out always send output, or to have the D/A converter "lock" the mode (for example, many home theatre D/A converters can be told that a signal is always, for example, a 48 KHz Dolby Digital signal, and then it won't drop a few samples determining the digital audio format.)"

TechTool Pro 4.x launch failure workaround

A number of readers are reporting problems launching TechTool Pro 4.x on Power Mac G5s. MacFixIt reader Sig Pfeifer is a good case example:

"I've installed TechTool 4 on a 1.8 Ghz G5, with Mac OS X 10.3.1. The results: Upon installation and re-boot, starting the application from the icon on my desktop resulted in TechTool Pro 4 immediately quitting. Also, booting up via the C key produced no results. Disc would not boot up. The spinning wheel just turned. I manually shut down my computer after 5 minutes."

We have since found that removing all PCI cards, as well as any external USB and FireWire devices will allow TechTool Pro 4.x to launch properly on some problematic G5s. Jonathan K, who had success with removing devices, writes:

"TechTool Pro 4.x still took far too long to boot (3 to 5 minutes.), but it did run the basic and intermediate tests. The basic test ran and allowed me to look at the test results. However, the intermediate tests, quit at the end and automatically restarted. Since I was running from the CD, all reports were lost."

Some users who have been running into problems while optimizing volumes with TechTool Pro 4.x have been able to resolve the issue by using the software's "Volume Journaling Tool" to disable journaling on before running optimization. Once optimization is finished, journaling can be turned back on with the same tool.

Noise Issues: Beeping, buzzing and more

General noise issues We've been receiving a significant number of confirmations and independent reports of noise with Power Mac G5 systems. However, there appear to be a number of different types of noise that users are experiencing:

A continual "chirping" noise that occurs when the Processor Performance setting in Energy Saver preferences is set to Highest. Changing this setting to Automatic or Reduced seems to avoid this particular noise.
A constant ticking or beeping noise whenever the computer is "idle" -- if processor-intensive tasks occur, the noise seems to disappear. (It's not yet clear to us if this is actually the same noise as the previous one, just described differently by different people.)
An overall humming of the machine that seems to be attributable to the power supply fans. Some users have taken to calling this a "fish tank hum" due to its similarity to the sounds produced by fish tank equipment. We mentioned yesterday that changing the Energy Saver settings to "Never" sleep seems to fix this problem for some people.
A "metallic screeching" or "static" that varies in frequency with processor load. Here at MacFixIt, we've experienced this issue on our own dual-2GHz G5 when resizing text clippings in the Finder. Reader Marc Jones points out that for him the "screech" is worse if he selects a QuickTime movie in the Finder or when using InDesign. At least in our case, installing Apple's CHUD tools and disabling the "Nap" feature completely eliminated this noise.

MacFixIt reader "Euge" has actually posted a sound file of various noises made by his dual-2GHz G5: "Begins with HUM-Buzz-Chirp; after 20s I disabled Nap to have only Hum-Buzz."

Reader Markus Altendorff has also posted a few excellent demo sound files, and provided a few informative comments:

After installing the CHUD tools (Apple, Developer software), disabling "CPU Napping" (some sort of power-down mode during idle clock cycles) makes the chirping go away (see below for more details - the chirping does not disappear completely)

My guess (and backed by a friend of mine, former electronics pro and now IT...) is that (cheap) filter coils in the PSU start to vibrate, similar to loudspeaker coils, when the CPUs switch between high and low power use, which can happen very often at 2 GHz clock cycle. Since disabling CPU napping results in the CPUs consuming a fairly constant current, the vibrations stop (the magnetic fields in the coils remain constant).

The bad thing about this is that the chirping also shows at the USB and Firewire ports, causing trouble when you try to use this computer in a recording studio - the thread at Apple Discussions contains quite a few complaints about how the G5 is barely usable for audio production because of this.

Several readers report that Apple replaced the power supply in their G5 as a result of noise issues. In some cases this solved the problem, but not in every case.

What makes these issues more than just annoying for some users is that some of the noises are transferred via USB and FireWire connections, and some are amplified by connected audio equipment -- reader Catherine Vibert reports that a "whining" noise is actually transmitted to the DIGI002 in Pro Tools via Firewire. These issues make affected G5 computers unusable for digital audio work.

Unfortunately, it's difficult for us to correlate noises with potential solutions because many people who have sent reports to MacFixIt have been vague about which noise their particular G5 is producing. There are clearly different problems and different solutions. If you send us email on this issue, please state which of the above "noises" your Power Mac G5 is producing and which, if any, technique reduces which noise.

Full-blown fans We've also received a number of additional reports of an issue where putting the G5 to sleep results in the fans revving up to full speed (which is startlingly loud if you've never heard it). Sometimes the situation can be resolved by waking the G5 up and then putting it back to sleep; however, sometimes the G5 will refuse to wake up, requiring a restart. We had this happen once to our G5 here at MacFixIt.

It appears that Apple technical support is recommending a PMU (power management unit) reset to some customers who are having fan irregularity problems. We've also managed to scrounge up a few unorthodox workarounds, including placing a thick pad of paper underneath the G5 to prevent vibration:

MacFixIt reader Paul Burton is one of the handful of G5 owners who experienced a problem where the system goes to sleep, the fans rev to full speed, and the G5 cannot be woken.

"I spoke with a technician from Apple and described the problem in detail ? Of course, it was the first time he had heard of such an issue with a G5. That said he suggested resetting the PMU pressing a button on the logic board inside the tower:

Open the computer and remove the clear dust cover.
Without removing the fan (in order to locate the button) - look down toward the lower left hand corner of the unit at the logic board (memory).
Now, follow the lower edge of the logic board over to the right until you see left bottom rear edge of the fan unit.
On the logic board, near this spot, you will see a small chrome square with a very small round flat-topped button in the middle.
Press and hold this button for three seconds.

Burton says that since doing this approximately three weeks ago, he has not had another occurrence of the fan revving/sleep problem.

Do not get trigger-happy though - pressing the CUDA or PMU switch repeatedly can result in damage to the PRAM battery, causing its capacity to shrink from years to days or less.

Meanwhile, Stan Goldberg found that putting a thick pad of paper under his G5 - which started making excessive noise after a few days of quiet operation - helped to dampen the vibration of the G5's case against his desk, eliminating one source of unwanted noise:

"When I first got my dual G5 about two weeks after they came out the unit was quiet as can be. I was amazed how silent it was. Then after the loud rev up upon sleep occurred after about five days the front fan seems to have come on and makes a consistent humming fan noise and won't turn off. There is also high pitch sounds that come and go and seem to be due to vibration. Putting thick paper pads under the lower supports helped with the vibration transmission to my wooden desk."

Power supply noise The noisy power supply problem generally manifests when Processor Performance is turned to Highest under Energy Saver/Options and the computer is idle. A recurring buzz/beep sound is made. If Processor Performance is turned to Automatic or Reduced, the noise is quieter, but still noticeable to some discriminating ears.

Oddly (or perhaps not) the problem disappears when iTunes' visualizer is turned on for many users.

A thread on Apple's discussion boards pertaining to this issue contains nearly 600 posts.

MacFixIt reader Craig Hein writes "I have had this problem since the day I received my 2x2 G5 in late September. Apple has be unable to offer any solution other than to replace the power supply, with no guarantee that the replacement will solve the problem."

"Furthermore, I am also afflicted with the problem where the computer goes into an unrecoverable sleep and the fans ramp up to full blast, so that upon returning to the room where I left a sleeping computer, I hear the whoosh of all fans blasting full speed. The only way to stop them is to hold the power button for 5 seconds to shut off the computer."

The most widely reported successful repair procedure involves replacing the G5's power supply unit. Customers have been hit-or-miss in their success obtaining this repair from Apple.

MacFixIt reader John writes "A number of people, including myself, are suffering serious sound problems on the new PowerMac G5. Playing sound through iTunes (some people have stated the problem also occurs with QuickTime, DVD player etc.) is just horrible. There are pops, clicks, sound dropout and something that I can only describe as digital 'wow and flutter' - I thought that had been consigned to history with the vinyl disc."

Our previously mentioned fix involves using Apple's CHUD tools to turn of "Nap" mode for the processors. However, as previously noted, this workaround only muffles the artifacts to an inaudible level in some set-ups. In highly sensitive, amplified sound environments, the chirps, beeps, and other strange noises are still noticeable.

Most reports indicate that the audio problems become worse after the G5 has been on for several minutes, or a processor intensive operation is taking place.

Rob Griffith's review of the Power Macintosh G5 includes a short audio clip comparing its fan noise level to that of a Power Macintosh G4/733.

Plastic door strips must be removed

MacFixIt reader Peter Wargo describes an strange problem with his Power Mac G5 that was resolved by a simple process documented in Apple's Knowledge Base:

"I had the oddest problem with my Dual 2 GHz G5 - If I removed the side door while it was running (not the shield, just the aluminum door), it would freeze up. I have two at work (identical) that don't exhibit that behavior, and when I ran the Extended Hardware Test, it worked fine. (Boy, do the fans get loud during those tests...) It booted and ran fine with the door removed."

Apple Knowledge Base article #86490 holds the solution. It states:

"When you set up your Power Mac G5 computer for the first time, be sure to remove the four protective plastic strips on the inside of the door."

Wargo says that as soon as he removed the plastic strips, he could successfully remove the aluminum door (leaving the clear heat shield in place) without freezing.

Blank screen from "cold start"; workarounds

There is a problem with some currently(?) shipping Power Mac G5s where a cold-start (the machine is off, then booted) results in a blank screen from which the user must manually reset via the Command-Eject-R key combination for normal startup to occur. [Note - Apple has reportedly revised the G5 architecture several times, and may have eliminated this issue on newer models]

Some users have had success eliminating this problem by using the age-old process of resetting PRAM. MacFixIt reader Robert Cramer writes:

"I have the same problem (blank screen from cold start) with my dual-2 GHz Power Mac G5 and have resorted to zapping the PRAM by selecting Option-Command-P-R immediately after switching power on. The procedure is in the Troubleshooting section of the G5 Manual."

In this case, it may not be the actual zapping of the PRAM that is doing the trick. Performing the PRAM reset causes your Mac to restart continuously until you release the key combination. It may simply be the repeated restart that is allowing users to startup properly.

Meanwhile, a report from Frans van der Geest indicates that the problem was temporarily fixed by removing, and then re-installing his RADEON card.

"A suggestion from Apple to remove and then re-install the video card seemed to work to fix the problem with a black screen when booting my Power Mac G5 'cold' at the beginning of the day. It booted up with the screen working for two days. Today, the first startup was black again: no video was initialized. Restarting directly again and the video was there again."

Some RAM modules may be too tall for the Power Mac G5

A MacFixIt reader reports that the Corsair Micro-manufactured RAM modules he bought at Fry's are too tall to properly fit into his Power Macintosh G5 Dual 2 GHz.

"I purchased the a 1 GB kit (two 512 MB Modules), PC3200 Pro speed. I love the flashing LEDs on the modules. The problem is that the modules are about 1/8" too high and therefore do not allow the PowerMac Fan Assembly to be pushed back into position. This creates a problems closing the door to the Power Mac. The sensor knows the door is not closed right, so the PowerMac is throttled down because of a problem with cooling."

"Fry's says this is an issue with Corsair, and Apple said that the G5 meets the electrical and physical specs for the PC3200 RAM module, therefore this is a Corsair problem."

As this report indicates, you should always check with the manufacturer of your PC3200 RAM module to make sure it is guaranteed to be G5 compatible.

False fan error message

Several MacFixIt readers have received the error message "2FAN/4/8: Fan for BACKSIDE" when running Apple's hardware diagnostic test on their new Power Macintosh G5 systems.

A moderator on the Apple Discussion boards has now provided official confirmation that this message may be erroneous, and suggests that readers who receive this or another fan failure message open the G5 and check that both the drive bay fan and the PCI slot fan are spinning. If they are, nothing is wrong.

If either fan is not spinning, the moderator suggests taking the computer to an Apple Authorized Service Provider for maintenance.

Crashes during iDVD encoding, solution

We have been receiving sporadic reports of problems with burning DVDs with iDVD using the internal Power Macintosh G5 SuperDrive. One reader writes

"I have found that iDVD tends to lock up a G5 machine during encoding. When it doesn't crash it fails to encode or go extremely slow. I had this problem on all three models at Two different Apple Stores. The Apple representatives were dumbfounded as well. "

This problem only occurs if you are using an iDVD install from the iLife disk or another source. These releases do not seem to work with the Power Mac G5. Try deleting all traces of iDVD from your computer and re-installing the application from the media included with your G5. You should be able to encode properly.

ATI Radeon 9800: features missing, noisy

ATI Radeon 9800: features missing, noisy ATI's Displays 4.1 software does not recognize the OEM version of the Radeon 9800 Pro graphics card that comes installed by Apple in the Power Macintosh G5, simply reporting it as "Unknown ATI Graphics."

MacFixit reader John Bennett writes "This effectively prevents one from using the full capabilities of the Radeon 9800 card, i.e FSAA (Ed.- full screen anti-aliasing) and other options. Until a fix is available it would seem to be better to not buy a G5 from Apple with the Radeon 9800 Pro pre-installed, and instead install the retail version 9800 Pro card on your own."

Another feature that is not supported with OEM cards is VersaVision, which allows you to rotate your desktop in either direction by 90 degrees for a portrait orientation, or flip it 180 degrees for an upside down view.

While the retail version of the card comes with a control panel that enables this functionality, the OEM version, shipping pre-installed in G5s does not.

Unfortunately, it looks like users will have to wait for a new software release from either ATI or Apple to gain this and other functionality, as it requires the addition of a new OpenGL extension.

Separately, users are complaining about the noise generated by the Radeon 9800 card. One poster to Apple's Discussion boards writes "Yes, my Dual G5 with Radeon 9800 Pro is quite a bit noisier than I expected all the time. It sounds much louder than my single G4 450. As reported in other threads, I did sound level tests on it which showed a 58-60 dB noise level at idle when measured from 1" in front of the system (using C weighting). For comparison sakes, my G4 450 is under 50 dB so my dual G5 is over twice as loud."

M Audio cards effectively not compatible with the Power Mac G5; fix coming

Yesterday we reported problems with the M- Revolution PCI audio card and Mac OS X 10.2.8 (apparently Mac OS X 10.2.7 as well). This, in conjunction with the fact that other M-Audio cards are not PCI-X compatible, effectively eliminates the company's cards from current compatibility with G5s.

Keith Lewington writes:

"Following myself emailing M-Audio with regard to G5 compatibility of their audio cards, It appears that only one card in the M-Audio range is PCI-X compatible and that is the Revolution Card, but as this is proving to have problems with 10.2.8 it now seems that nothing is compatible.

"There is nothing on their Web site regarding this matter and I know of two people that have purchased cards from them recently, to be used in G5's, that were not told this information at the time and will now be very disappointed."

A MacCentral article indicates that M-Audio is working on G5 compatibility.

Resources

Working with Optical audio...

TechTool Pro 4.x launch fa...

Noise Issues: Beeping, buz...

Plastic door strips must b...

Blank screen from "cold start"; workarounds

Some RAM modules may be to...

False fan error message

Crashes during iDVD encodi...

ATI Radeon 9800: features ...

M Audio cards effectively ...