Computer processors generate large amounts of heat as they operate, which if left unchecked can destroy the computer. The Compaq A900 laptop computer uses a small fan to circulate air through the computer, which passes over the that sink attached to the processor. As long as the fan is running, the computer should remain within acceptable operating temperatures, but should the fan fail, the computer will likely overheat and shut down. To correct the problem, you will have to open the computer and replace the defective fan.
Turn off your computer and disconnect the AC power adaptor. Remove any external devices from the computer, such as a USB drive or network cable.
Close the computer's cover and lay it facedown on a table with the front edge facing you. Press the battery latch to the left and at the same time lift the front edge of the battery up. Rotate the battery to the rear to remove it from its bay.
Touch the metal VGA connector on the computer's rear to ground yourself. Repeat this every few minutes to ensure a static electric charge doesn't build up, which can damage the computer's electronic parts.
Use a Phillips screwdriver to loosen the two screws on the hard drive compartment cover, located in the front-left corner of the computer base. Remove the cover by lifting the left edge and sliding the cover to the left. Use the plastic tab on the hard drive to lift it up and slide it to the left out of the compartment.
Remove the two screws from the memory module compartment cover and lift the cover off the base. The memory module compartment is located just forward of the battery bay on the right side. Pull both antenna cables off their connector posts to disconnect them.
Rotate the computer so you're facing its left side. Remove the Philips screw that attaches the optical drive, located approximately 6 inches from the left edge, along the centre-line of the optical drive. Open the optical drive tray by inserting a thin piece of wire, such as a straightened paper clip, into the hole on the tray door. Grasp the tray and slide the optical drive out of the computer.
Remove the 10 switch cover screws from the bottom of the computer. Two screws are in each rear corner and six screws in the battery bay. Remove the single keyboard screw located about 2 inches to the rear of the hard drive compartment's right edge. Turn the computer over and open the display until its flat. Lift the left and right edges of the switch cover to unsnap it from the top cover and lay it on the display.
Remove the three screws from the top edge of the keyboard. Lift the rear edge of the keyboard, slide it to the rear and lay it on the display. Rotate the keyboard ribbon cable zero insertion force, or ZIF, connector up to unlock it and slide the cable to the rear to detach it. Remove the keyboard.
Lift the switch cover ZIF connector to unlock it, slide the ribbon cable to the rear to disconnect it and remove the switch cover.
Lift the display cable connector, located near the left-rear corner, straight up to disconnect it from the motherboard. Pull the microphone cable, located in the centre-front of the computer, to the left to disconnect it. Remove the antenna cables from their routing clips along the top of the computer case.
Support the display assembly with one hand as you remove the two screws from each of the display assembly hinges and lift the display up, off the computer base.
Turn the computer over with the front toward you. Remove the 14 top cover screws from the bottom of the computer case. Six screws are along the front edge, one on the left edge just forward of the optical drive bay, two along the right edge, one on the rear edge on the right side of the battery bay, one to the right of the hard drive compartment, two to the rear of the hard drive compartment and one in the memory module compartment. Remove the two screws from the top edge of the optical drive bay.
Turn the computer over with the front toward you. Disconnect the LED board connector, located just behind the left edge of the TouchPad, by pulling it toward you. Lift the TouchPad ZIF connector and slide the TouchPad cable to the rear. Remove the single top cover screw located just behind the TouchPad connector. Grasp the rear edge of the top cover, lift it up and swing it forward to remove it.
Pull the fan cable connector to the right to disconnect it form the motherboard. The fan is located in the left-rear corner. Remove the single screw from the right side of the fan and lift the fan straight up out of the computer.
Put the new fan into the case, replace the screw and attach the fan cable. Replace the top cover by first aligning the front edge and rotating it down to the rear. Press along its edges to snap it into place. Replace the top cover screw and reconnect the TouchPad and LED board connectors.
Turn the computer over and replace the 14 top cover screws and the two screws in the optical drive bay.
Turn the computer over and arrange the display assembly on the hinges. Replace the two screws in each hinge. Reconnect the display and microphone cables and route the antenna cables through their channels. Feed the antenna cables down through the hole to the memory module compartment.
Lay the switch cover on the display and slide its ribbon cable into the ZIF connector. Press the connector down to lock the cable in place.
Lay the keyboard on the display, slide the ribbon cable into the connector and press the connector down to lock it. Slide the keyboard to the rear, inserting the tabs on the front edge of the keyboard into their slots. Replace the three keyboard screws. Snap the switch cover into place.
Close the display and turn the computer over. Replace the 10 switch cover screws. Snap the antenna cables onto their connector posts and replace the memory module compartment cover. Slide the optical drive into its bay and replace the screw. Insert the hard drive into its compartment from left to right and press the left end down into the compartment until its fully seated. Replace the hard drive compartment cover and tighten the screws.
Replace the battery, turn the computer over and reconnect any external devices, including the AC power adaptor.
Make sure you mark the screws and secure them to prevent loss. Using a digital camera to document the disassembly steps will help you during reassembly.