The motherboard in a Dell Optiplex 745 desktop computer system can be replaced when an on-board component fails, or when the motherboard no longer functions. The motherboard is proprietary and generally must be replaced with a factory original part that matches the system case exactly, as few aftermarket boards were created to fit the case design. There were four different models of Optiplex 745 created by Dell, and those include the desktop, mini-tower, small form factor and ultra small form factor editions.
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Things you need
- Anti-static wrist strap
- Screwdriver set
- Wide plastic scraper or expired credit card
- Isopropyl alcohol 91%
- Soft, lint-free cloth
- Thermal heat sink compound
Power off the computer, and disconnect the power cord, video cable, speakers, network cable, mouse and keyboard (and any other cables or devices) from the Optiplex 745.
Open the case cover, then connect the alligator clip end of the anti-static wrist strap to the metal chassis or to the ground terminal on an electrical socket. Connect the other end to either wrist.
Disconnect the main power cable from the motherboard by squeezing the small clip in the middle of the connector while pulling straight up. Disconnect the auxiliary power connectors and any data cables and front panel connectors from the motherboard.
Remove any expansion cards by releasing the clamp that holds them in place, or removing the single screw that attaches them to the chassis, then pulling the card straight up out of the slot.
Remove the brackets that hold the optical and hard drives in place if they are in the way of removing the motherboard. This will vary by system and depend on which style of case the Optiplex 745 has, as some models, such as the mini-tower, may not need to have any drives removed to replace the motherboard.
Release the heat sink retaining clip and gently pry the wide plastic scraper or expired credit card between the CPU and the heat sink to break the bond that is formed by the thermal heat sink compound. Remove the heat sink from the top of the CPU, but leave the CPU inserted in the motherboard for cleaning.
Scrape all of the old thermal heat sink compound off the heat sink and the CPU with the wide plastic scraper or expired credit card.
Pour a small amount of Isopropyl Alcohol 91 per cent onto the soft, lint-free cloth. Scrub the remaining deposits of thermal heat sink compound off the heat sink and top of the CPU. Be careful not to touch the surface of the CPU or heat sink directly to avoid contamination, which could lead to uneven cooling.
Arrange the new motherboard so that it is in the same orientation as the old motherboard, with the ports facing the same direction, in order to align it for the CPU transfer. Raise the CPU locking lever on the new motherboard.
Raise the CPU locking lever on the existing motherboard, and gently grasp the CPU by the edges and pull it straight up out of the socket, placing it down slowly into the socket on the new motherboard. Ensure that pin 1, as indicated by a small triangular marking on the CPU, matches the socket, which also has a small triangular marking. Allow the chip to drop into the socket under its own weight and then press down gently on the edges of the CPU. Lower the locking lever.
Apply a thin layer of thermal heat sink compound to the top of the new CPU and place the heat sink squarely on the CPU. Lock the heat sink retaining clip in place.
Press outward and down on the small plastic retention tabs for the RAM slots on the new motherboard to prepare them for RAM module installation.
Press outward and down on the small plastic retention tabs that are holding the RAM in place on the old motherboard until the RAM modules rise up slightly in the sockets. Grasp the RAM modules by the ends and pull them straight up. Transfer the RAM modules directly to the new motherboard as indicated by the small key notch in the module which lines up with a small plastic tab in the slot. Push the RAM modules down into the slot using firm, even pressure until the plastic retention tabs click into place and lock against the ends of the modules.
Remove all of the screws that are holding the motherboard in place, then lift up gently on the edge of the motherboard near the front panel. Pull the motherboard toward the front panel slightly until the rear ports are clear of the rear port bezel and remove the motherboard from the Optiplex 745 system.
Insert the rear ports of the new motherboard into the rear port bezel and push it against the back of the case gently until all of the ports are protruding through the bezel, then lower down the motherboard onto the standoffs. Fasten the motherboard in place using the same screws that were holding the old motherboard in place.
Install any expansion cards and reconnect the data and power cables to the motherboard as well as the front panel connectors.
Tips and warnings
- Use Isopropyl alcohol 91% instead of 70% as the difference is made up with water, which can cause corrosion over time on sensitive electronics.
- Static discharge can destroy sensitive components such as the RAM and CPU and an anti-static wrist strap or other similar device should always be worn when working on computer.
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