Power Mac G4 MDD fans replacement: maybe insufficient airflow?

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robegian's picture
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In the discussion about silencing a Power Mac 9600, I described what I did to silence a Power Mac G4 MDD: I replaced three fans and disconnected one (the side panel fan cooling the DVD burner, which I never use) — consequently the machine got remarkably quiet.

For your convenience I quote here below the rest of the description:

Quote:

I placed one 120mm SilenX iXtrema 120 (noise level 18 dB, air flow 90 CFM) for the CPU, and two Xilence Slim 60mm Case Fans inside the PSU (22dB, 29.7 CFM).

I followed some instructions found here:
http://coolstuff.wordpress.com/2007/02/19/powermac-g4-mdd-cooling-and-noise-reduction/

And here:
http://www.xlr8yourmac.com/systems/g4_mirrored_drive_doors/noise_reduction/g4_ddr_noise_reduction.html

I faced just one problem: the iXtrema 120 sports three grey wires while there are only two pins on the motherboard, so I had to figure out which wires to connect (see photo — turned out the central wire is +).

The two 60mm fans are considerably slimmer and move less air than the original fans, but this doesn't seem an issue. Here's an image showing the new and the old fan side to side, and here's another one showing the new fans placed in the PSU.

Here's a picture showing the innards of the PSU, and the fan's connections. Watch out the 450V capacitors in the PSU (although they probably don't represent a threat).

Now I'm afraid the SilenX iXtrema 120 (whose task is keeping down the CPU's temperature) is not moving enough air, because when I put a hand near the fan I barely feel a gentle breeze. I tried comparing the iXtrema 120 with the original fan and indeed with the latter I felt way more air movement (and heard WAY more noise) — about double the iXtrema 120's. As an experiment, I tried powering the iXtrema not through the motherboard's pins but through an unused SCSI molex, and predictably the fan span at full speed, moving a lot of air (undoubtedly more than the original fan powered by the motherboard) and generating a considerable amount of noise (although less than the original fan).

My doubt is: could this «lazy» fan cause some hardware failure due to insufficient cooling?

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robegian's picture
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Re: Power Mac G4 MDD fans replacement: maybe insufficient ...

Searching the net brought some good news: looks like my single-processor MDD G4 doesn't generate quite an amount of heat, so the «limited» airflow on the CPU shouldn't be a problem. In fact, in use the CPU's temperature never went beyond 40°C.

I purposely used the G4 in Mac OS 9 (which doesn't feature a 'nap' function) playing F-18 Korea for half an our, then I rebooted in OS X to read the temperature and this is what I got.

After reading this report, I detached the loudspeaker in order to obtain one more ventilation hole, probably useful especially for the PSU fans — even if I didn't add a fan to help air getting in. The loudspeaker now is resting on the 5.25" bays, and it's still functional although this G4 usually relies on a pair of nice external Apple Pro Speakers.

I won't use much this G4 with OS X (since I'm using it mostly as a host for the Korg OASYS PCI card, which needs Mac OS 9) but just in case I downloaded CHUD 3.5.2, after reading this discussion:
https://discussions.apple.com/message/16916694#16916694

By the way, I monitored the temperature with Temperature Monitor (of course!):
http://www.bresink.com/osx/TemperatureMonitor.html

One more thing: I discovered that when I plug in a FireWire device, the PSU fans audibly reduce their speed (!). This happens both with the original and the new fans, and it's an inexplicable behaviour.

robegian's picture
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Re: Power Mac G4 MDD fans replacement: maybe insufficient ...

Just to keep you informed: the G4 is working great, and in silence Smile

I also upgraded its Combo Drive to a SuperDrive. Originally I installed a Pioneer DVR-109, supposedly new, but it's been a disaster: almost all DVDs I burned (a dozen of Verbatim DVD+R and DVD-Rs) failed the verification process. Consequently I installed an LG GSA-H50L, which is happily burning anything without errors.

Since the G4 now hosts two SuperDrives, I placed back the side panel fan (though replacing it with a more silent model).

markyb86's picture
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Re: Power Mac G4 MDD fans replacement: maybe insufficient ...

robegian wrote:

One more thing: I discovered that when I plug in a FireWire device, the PSU fans audibly reduce their speed (!). This happens both with the original and the new fans, and it's an inexplicable behaviour.

Firewire and the logic board fan connectors probably share a power source. Just like if you use a piggyback molex fan connector between a hard drive or optical drive, the fan speed will change depending on power usage.