After moving cross-country, I noticed that my trusty (Gen. 1) Dual 2GHz G5 was making more noise than usual. It’s an unusually quiet computer, so I set about looking for reasons for it’s sudden, roaring outburst. In particular, one CPU was running almost 40 degrees fahrenheit hotter than the other.

Possible causes for the increased noise included:

1. • Our new place is not between two freeways, like One Pearl Place.
   

2. • My sharpened, zen-like attention to all things great and small.
   

3. •Jostling of the machine during our freighted move.
   

4. • Gradual buildup of dust and pet hair in the heat sinks, which insulates the radiating surfaces - this reduces the effectiveness of the radiating surface of the heatsinks. In addition, crud on the leading edge of the fans causes them to be less efficient at moving air over the heat sinks.
   

5. • Gradual hardening and decreasing effectiveness of thermal transfer compound between the G5 and the heat sink.
   

6. • My imagination.
   

When I worked at Apple long ago, I was happiest taking apart PowerBooks and desktop CPUs looking for failures (although that’s not what I was paid to do, exactly), so I decided to put that skill to work cleaning my First generation Dual-Processor G5 and replacing the thermal transfer compound shipped from the factory.

Here’s how I did it, and what I learned. Read the entire guide and look at all the pictures before beginning.

Conventions and Terms:

Notes are colored Orange. Notes indicate information that is helpful, potentially time-saving, or which may not be obvious.

Warnings are colored Red. Warnings indicate information that is critical to successful completion of this process. Read all warnings.

FYI: For Your Information sections are colored Blue. FYIs are information that might be interesting to anyone crazy enough to actually do this.

Forward: When viewed from the access panel side, forward is left, toward the front of the computer.

Rearward: When viewed from the access panel side, rearward is right, toward the back of the computer.

-Torx T10 driver. (To release heatsink assembly from the logic board.) A driver with an eight-inch shaft would be perfect. Stop giggling.

-Small Phillips-head screwdriver.

-Small flathead screwdriver.

-”Can of Air” duster. DO NOT USE COMPRESSED AIR GUNS.

-Ridiculously overpriced tiny tube of Arctic Silver thermal transfer compound. You can find this at CompUSA or Fry’s.

-PecPads or similar lint-free non-abrasive wipes. (Get PecPads at your local camera store or at Calumetphoto.com)

-Q-tips or similar stick-like wiping tool.

In this document, the words “heat sink” are used to denote heat sinks, radiators and heat pipe assemblies that are factory assembled. Heat sink assembly is used to refer to the heat sink and PCB components when assembled.

I use and recommend Wiha brand precision tools for jobs like this. They rock.

Disclaimer: If you don’t have the training, tools and good sense to do this properly, don’t even try it.

I’m not responsible if you follow these instructions and screw up your machine. In fact, I wouldn’t recommend this procedure for anyone who isn’t trained to work with extremely delicate electronics. An Apple Authorized Service Provider has this knowledge, and may perform this process for you if your machine is out of warranty. If you do attempt this procedure, set up and work in a static-safe environment.
If you don’t have the training, tools and good sense to do this properly, don’t even try it.
You could render your computer inoperable or cause serious damage to peripherals connected to the logic board of your computer, leading to data loss, loss of productivity, tears, and subsequent heavy drinking.

Remove the Heat Sink Assemblies

1. 1. Remove the side access panel.
   

2. 2. Remove the plastic air deflector panel.
   

3. 3. Remove the slide out CPU pusher fans.
   

4. 4. Remove the decorative “G5” heatsink covers.

   

   
       -Use the small flathead screwdriver to gently push the snap-pins toward the center of the heat sink assembly to release the forward grey G5 cover pins. Very gently rotate the cover rearward to release the rear pins. Repeat for the remaining cover.
   

5. 5. Use the Torx driver to unscrew the heatsink assembly fasteners. See Figure 1 for the location of these screws.
   Note: Do not remove the screws from the heatsink assembly yet!
   

6. 6. Using firm pressure against the front and rear edges of the heatsink, lift the heatsink assembly straight up to remove it.
   Note: You may have to apply a slight front-to-rear rocking motion to free the heatsink module from the logic board connector, but be extremely gentle here.
   

7. 7.Place the heatsink on a static safe work surface. Label each module - upper and lower.
   
   

1. 1. Place the heat sink on a clean work surface with the bottom of the printed circuit board (PCB) facing up.
   

2. 2.Remove the six small phillips-head perimeter screws holding the PCB to the heat sink assembly. (see Figure 2.)
   

3. 3.Remove the four spring-loaded centered leveler screws from the PCB with a hex key or the T-10 TORX tool. (see Figure 2.)
   

4. 4. Detach the plastic clips holding the cache heat sink to the main heat sink assembly.
   

5. 5.With the bottom of the PCB facing up, and the cache heat sink to your left, rotate the cache heat sink and PCB to the right and away from the main heat sink.

   

   
   

Do not remove the cache heatsink from the processor PCB.

Cleaning and Preparing the Heatsink Assembly Components

Definitions:

Processor package: The die, BGA, capacitors, and other components of the processing chip.

Decoupling capacitors: On the processor part, these are eight brown rectangular components. Special care should be taken to avoid applying any thermal compound to or between these parts, as it could increase the capacitance of the components.

Die: The silver, mirror-finished part of the processor chip. The G5 is rectangular, rather than square, as with the G3 and 604e. Treat this area with extreme care. Do not touch it with anything but a PecPad or soft Q-Tip.

BGA Package: This is the ceramic and solder “base” of the processor package. Your G5 should be slightly off-white in color. This material is tough, but should be treated with care.

Gasket: Apple uses a clear insulating gasket in their G5 application to expose only the die to the heat sink base. According to IBM, it may be permissible to leave this out of the stack, but I recommend reapplying the gasket. A surround of high temperature foam adhesive is used to affix the insulator. Remove this part with care before cleaning old thermal compound residue from the processor, and reapply the gasket carefully after applying new compound.

Cleaning Heat Sinks and PCB:

1. •Use canned air to blow the dust bunnies from the main and cache heat sinks. Dust all six sides of each heat sink.
   

2. •Optionally, contact dust each level of the heat sinks by passing a PecPad stuck over a popsicle stick into the heat sink. Do not whack the copper heat pipes.
   

3. •Using a fingernail or the tip of a credit card, remove the plastic insulator cover from the top of the processor. Don’t touch the processor.
   

4. •Use denatured alcohol or high-end tape head cleaner and a Q-Tip or PecPad to remove old thermal compound residue from the processor.
   

5. •Take care to remove all original thermal compound residue from the eight brown decoupling capacitors around the processor die.
   

6. •Once again, avoid touching any of the parts on the PCB. Handle the PCB by the edges or by the cache heat sink.
   

Applying new Thermal Compound:

1. 1. Apply a dot of thermal compound to the processor die only. Use an amount about equal in volume to half a grain of short-grain rice. A little goes a very long way here.
   

2. 2.Use a credit card or other non-conductive straight edge to smooth the thermal compound over the die evenly. Arctic Silver has a good tutorial - use it.
   

3. 3. Reapply the insulating gasket. Take care that the gasket does not move between now and when the leveler screws are fastened!
   

Reassemble the cache heat sink and PCB:

1. 1. Mate the PCB and cache heat sink by lining the perimeter screw posts over the screw holes and pulling the PCB up onto the posts.
   

2. 2. Flip the assembly over and insert the six perimeter screws.
   

3. 3. Insert the four leveler screws and tighten until the spring-loaded posts engage. Cross-tighten (like a car wheel’s bolt pattern) until the screws are just past finger tight. Unfortunately, I don’t have a torque rating, but once the PCB is sandwiched between the level screw and spring post, there’s very little room to tighten. Over-tightening will probably ruin the screw before the PCB, but either way, you won’t be doing any computing unless all four corners are equally tight.
   

4. 4. Clip the cache heat sink to the main heat sink assembly.
   

5. 5. Visually inspect the PCB/insulator/heatsink sandwich to verify that the insulator has not slipped during reassembly and covered the processor die.
   

6. 6. Reassembly is reverse of disassembly.
   

7. 7. Test for normal operation using software that pegs the CPU. I suggest running an iTunes visualizer full screen, and running memtest (or Rember) simultaneously.
   

A few things I learned:

1. • On Dual-CPU machines, the lower CPU can be removed and the computer will operate as a single CPU machine - but the lower CPU cannot be alone, or the machine will not boot. (see screen shot below)
   

2. • Inadvertently switching the upper and lower CPU modules will force a fan re-calibration. The thermal management unit o the logic board will see a new CPU card ID in the processor slot and run the fans at full tilt until the calibration is performed. If you accidentally switched the modules, just swap them back to resolve this. Unfortunately, only Apple authorized Service Providers have the calibration software - so label the CPUs before disassembly to avoid troubleshooting later.
   

3. • Use good-quality thermal transfer compound. The stuff from Radio Shack is not meant for extreme die temperatures.
   

4. • IBM has some good documentation about he G5’s thermal characteristics here, including a mention of Arctic Silver as a suitable mating compound.
   

5. • IBM and Apple collaborated on a white paper about the G5’s heatsink design. You can find it here.
   

6. • While my CPU temperatures still differ, it is now by a maximum of only 30 degreesƒ instead of 40+. Section 7.1 of this IBM white paper might explain why - different G5s at the same frequency may in fact have different current leakage.
   

So, is the machine quieter now?

Yes!

My G5 now fan-cycles with CPU load like when it was new, instead of running at a constant, higher speed. My CPU die temps went from a reported 105/143 degrees to a more normal 100/122. The low-load fan noise is almost totally silent now. With NAP mode switched off and both CPUs at 95% or higher, maximum reported die temperature doesn’t exceed 144 degrees ƒ with ambient temps of 77 degrees.

I suspect that a combination of all the factors I listed at the beginning of this article contributed to the increased fan RPM and subsequent noise. The new thermal compound may have contributed to better heat transfer from the die to the heat sink, but I doubt that factor contributed much to the improvement.

Feedback?

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