The power supply is what provides electrical power to the parts in a computer. It takes the 90-263 volts AC from the wall outlet and converts it to the 3.3, 5, and 12 volts DC needed by the parts in the computer.
Here are pictures of the power supply in this computer.
The secondary side of an SMPS (Switch Mode Power Supply) contains components for rectifying the high frequency AC from the primary side back to DC and cleaning up the DC power so it is as clean as possible. Dirty DC power results in an unstable computer.
The protection IC in a PSU is responsible for monitoring the PSU and safely shutting it down if something goes wrong, such as a short circuit or an overload.
This power supply is not an auto-ranging supply. You must manually select it's input voltage with a switch. That switch is connected to these 2 wires. When the switch is on the 120V setting, these 2 wires are shorted together, enabling a voltage doubler circuit that is required for the supply to operate on 120 volts AC. When the switch is on the 240V setting, the wires are not connected together, and the voltage doubler is disabled. If the voltage doubler is enabled when the power supply is connected to a 240V supply, it will kill the power supply because too much voltage will be applied to components on the primary side.
Voltage Doubler Circuit Switch Wiring
These are the transformers on the primary side of the power supply. They step the high-frequency 120 volts AC down to 12, 5, and 3.3 volts AC. The current is still AC because it has yet to go through the rectifiers on the secondary side of the PSU and be turned back into DC current.
Primary Side Step-Down Transformers
Here are some of the primary-side AC line filtering components. The 1 yellow component is an X capacitor. It connects between line and neutral. The 2 blue components are Y capacitors. The large copper coil is a choke. All of these are EMI and RFI filtering components. I've written a short stub on X and Y capacitors here.
Primary Side Filtering ComponentsThis is glue. It stops the components from shaking around. It starts off white and flexible, but it eventually turns brown and becomes conductive. This glue must be removed before it turns conductive, or else it will kill the power supply. Here, you see it about halfway between white and brown.
Here, we see more of this glue that I'm eventually going to have to remove.
IEC C13 Input Socket and 115/230V Selector Switch
Here is the (rather dusty) PSU fan. It has since been cleaned up.
This is a small daughtercard that is responsible for the cooling fan's speed control. The hotter the PSU, the faster the fan runs, and vice versa.
The Cooling Fan's Speed Controller
