Practical -80 :- Power Supplies and Motherboard Layout

Power Supplies

Power supplies typically look like a rat's nest of wires. These wires are separated into two main groups: motherboard power connections and peripheral power connections.

To begin with, the motherboard requires multiple levels of voltage and multiple sources for proper operation. Therefore, the connectors to the motherboard tend to appear complex. The figures below show the two main types of motherboard power connections that you will see.

 

Older AT Power Supply Connections for a Motherboard

Newer ATX Power Supply Connections for a Motherboard

Unfortunately, the power supplies in our Dell machines do not follow the standards. They are actually a combination of the new ATX style and the older AT style. The connectors, however, are keyed so that there is only one way for them to be connected.

It is particularly easy to destroy a motherboard with the older AT-type power supplies by connecting the power connections wrong. As shown in the diagram, there are two flat, white connectors with six wires going into them. These are the wires that provide power to the motherboard. They connect in a line to connectors on the motherboard. 

Note: These connectors can easily be swapped as they are not keyed. The motherboard will be ruined if this happens! Make sure to plug them in so that the black wires of both connectors are next to each other. If you are unsure, ask before plugging them in.

As for the rest of the wires coming out of the power supply, these provide voltage to the peripheral devices installed inside the PC's housing. These include hard drives, floppy drives, CDROMs, and other storage devices. Each of these connectors has four wires: two providing a ground or 0 volt connection, one for 5 volts, and one for 12 volts. There are two styles of this type of connector: a smaller (about 1/2" wide) white connector that provides power to the floppy disk drive and larger (about 1" wide) connectors that go to all other devices. The latter has a trapezoidal shape when viewed from the end.

 

Power Supply to Motherboard Diagram

Every PSU installation will require 2 direct connections to your motherboard. One for the main motherboard power, and one for the CPU power. The locations where you plug these in on a motherboard will generally be around the same area from board to board. Here's where you connect the power supply cables to the motherboard for our example build:

Motherboard Layout

In this exercise, your lab computer will be disassembled, all that is except the motherboard. The motherboard is the large printed circuit board that is mounted to the bottom of the computer's case. Motherboards have standard mounting holes so that the same computer case can be used with different boards.

 

All of the components of a computer system are connected in some way to the motherboard. It is those connections that this lab is meant to show. In the end, you should be able to connect any device to the motherboard or even swap motherboards. To upgrade a computer's motherboard, simply disconnect all of the peripherals, unmount the old motherboard, mount the new motherboard, and reconnect the peripherals.

The figure below represents a common (yet rather old) motherboard.