Checking the Thermal Grease
Warning: Whenever the heatsink is separated from the logic board (even if you are installing the same heatsink or board), the thermal grease must be checked and possibly replaced. Failure to do so can cause the computer to overheat and be damaged.
1. With the heatsink removed, check the underside of the heatsink:
• If it has a thin sheet of transparent film covering the square heatsink pads and pre-applied thermal grease, then you do not need to reapply thermal grease. Do not remove the thin film. Skip step 2 and go to step 3 to clean up any excess thermal grease that might have squeezed out onto the chips. Then go directly to step 8.
• If you are installing a new heatsink and it is packaged with clear, rigid plastic, remove the clear plastic from the heatsink plate. Because the heatsink includes pre-applied thermal grease, skip step 2 and go to step 3. Then go directly to step 8.
• If the thermal grease is directly on the heatsink pads (as shown in step 2), continue with the remaining steps in this procedure.
2. Caution: This step is required only when the heatsink and logic board are removed to replace a later part (such as the bottom case) and the same heatsink and logic board will be re-installed in the computer.
Use a black stick to remove as much thermal grease as possible from the two chips on the logic board and the two pads on the heatsink.
3. Use an alcohol wipe to completely clean the residual thermal grease from the two chips. (If you are replacing the logic board with a new one, skip this step.) Important: Use extreme care not to damage the logic board components.
- 4. Use an alcohol wipe to completely clean the two pads on the heatsink.
5. Caution: The syringe steps for this procedure are required only when the heatsink and logic board are removed to replace a later part (such as the bottom case) and when no new heatsink with pre-applied thermal grease will be installed. Refer to the heatsink conditions in step 1 for details before attempting to replace the thermal grease.
Note the contents of the syringe of thermal grease.
Important: One syringe (922-7144) contains 0.3 to 0.35 cubic centimeters (cc) of thermal grease. That is enough for 0.1 to 0.12 cc of grease per chip for up to three chips. Because this computer has only two chips, the last 1/3 of thermal grease remains in the syringe. Use one-third of the syringe contents per chip. Using a felt-tip pen, mark the 1/3 points on the syringe before applying the first dab.
6. Using the syringe, put a 0.1 to 0.12 cc dab of thermal grease, in the center, on the mating surfaces of both chips, as shown below. Apply the grease only up to the line that you marked on the syringe.
Important: Use one-third of the syringe contents per chip, so in this case, 1/3 of the thermal grease will be left in the syringe when you are done. Although the amount shown appears to be plenty of grease, this is the correct amount that has been tested and verified on the production line.
Important: Avoid unnecessary contact with new thermal material, as dirt and body oils reduce the material's conductivity.
7. While centering the heatsink pads over the two chips, lower the heatsink onto the logic board and press on the areas where the screw brackets on the heatsink meet the standoffs on the board. Make sure the heatsink is level on the board before installing the screws.
8. Install the heatsink (using the screw sequence shown below), and reassemble and test the computer.
Note: Make sure the heatsink includes the gray, adhesive sponge strip that sticks to and runs along the top of the copper pipe. (A new heatsink kit includes the gray strip, ready for installation.)
9. Replacement Note: If you replaced the heatsink from a kit that includes the thermal sponge, install the thermal sponge over the two thermistor connectors.
- Make sure the connectors are fully seated.
- Remove the adhesive backing from the sponge, and place the sponge adhesive side down over the two connectors.
- Make sure the sponge sticks to and completely covers both connectors. (The actual color and appearance of the sponge may vary slightly from what is included in the kit.)
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