Power Mac G4 Mirrored Drive Door Noise Modification

Hans Koenig offers a hardware modification that dramatically reduces the temperature (and therefore loud fan operation) experienced when running Mac OS 9 on a Power Mac G4 Mirrored Drive Door system.

The hardware modification could void Apple's warranty, and should be applied with extreme caution, if at all:

"Make (or get someone to make) a connector adapter: fan socket to standard hard drive power connector. Connect the fan power lead to the 5V HD lead (not the 12 V) and bridge the free fan connector pins at the mother board with a 20 ohm 10 watt (18 watt in the picture) resistor. (From fan data: 12V 600 ma P= IV = 7.2W)) Plug the fan socket into the adapter and the HD socket into one of the available free hard drive connectors inside the Mac. The big fan will now run constantly but the 5V connection runs it at much reduced speed.

"The resistor is necessary because the heat sensing circuit needs to see a load when it decides to supply power to the fan. If the load is not there the circuit unceremoniously shuts off the Mac, a nice safety feature, Apple! This resistor is big and needs to be mounted to the metal side wall of the Mac.

"This Mac running OS 9.2.2 has been exercised for some four days now working with Netscape, Canvas, Excel and GraphicConverter open and doing their thing: Surfing, manipulating photographs, doing statistics pretty much constantly. No temperature rise to note during these operations."

Feedback or workaround possibilities for this issue? E-mail late-breakers@macfixit.com

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