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Building a Basic Computer - Part 2

 

The Case Fans

Virtually all computer cases need forced-air cooling. For low power computers, the power supply fan is enough. For today's computers with more powerful processors and high speed hard drives, you need additional cooling. The most common fan setup has one fan pulling fresh air into the front of the case and a second one forcing warm air out of the rear of the case. Here you can see the front grill of the case. The front panel has been removed.

To allow more air flow with less noise, many people cut the fan grill out as shown below. Most of the cases are made of soft enough material that it takes very little effort to cut the stamped grill from the case. Sometimes the same thing is done with the rear case fan. When this is done on the rear, the fan is typically protected with a wire grill that has very little effect on air flow and does not add any significant noise (from the air flowing through it).

To keep the wires away from the fan blades and any sharp metal, you need to use a wire-tie or two.

Below you can see that the fan has been installed. Also notice that I bent some of the metal tabs back towards the fan. I did this because it looked like they may cut into the front USB wiring.

The DVD Drive

Below, you can see the rear of the DVD drive. It's essentially the same as the one on the storage devices page but this one has better markings for the different connectors.

The computer I'm assembling here is black. The DVD drive has both black and beige bezels but the beige bezel is installed from the factory. It's relatively easy to change the bezel and drawer cover. Here you can see the bottom of the drawer. There are two catches holding it in place. To remove the drawer cover, you gently pull the catch away from the drawer until it can be slid upwards. To install the new cover, you simply slide it down over the drawer.

To change the bezel there are several latches (one on each side of the drive). Push the catches inwards with a small screwdriver (being careful not to slip and allow the screwdriver to enter the drive). After the original bezel is removed, you simply snap the new bezel into place.

From this angle, you can see the installed drives and fan. For the tutorial, I ordered a drive cooler and figured I'd use it in this system. If I didn't have a drive cooler, I would have mounted the hard drive directly in front of the front case fan. It would have slowed the air flow very slightly but it would have kept the drive cool. As I said earlier, todays drives need to be cooled. If you don't use auxiliary cooling, the drives will run hot. If you have a drive that runs too hot to continuously hold your hand on it, it needs to be fan cooled. Generally, it requires only a small amount of air flow over the drive to make a big difference.

Note:
When mounting the drives, you need to use the shortest screws possible. Ideally, they will have only 6 or 8 threads and when installed into the drive will have no more than about 1/16 of an inch inside the drive. Long screws can damage internal components and ruin the drive. Below, you can see the damage done by a screw that was too long (no mounting screw should ever make contact with the drive's circuit board). The damage seems minor but this drive will never work again.

Front Panel Connections

The following image shows the connections from the front panel of the computer case. There are generally four connectors (for the power indicator LED, hard drive activity indicator LED, reset switch and power switch). The polarity for the LEDs is important. If you have the polarity (positive/negative) reversed, the LEDs will not light up. If you look closely at the area just below the connector header, you can see a small '+' (just below the small number '2'). That tells you that that terminal is the positive terminal. The switch connections are not polarity sensitive.

Here you can see the front panel USB connector where it plugs into the motherboard.

The following image shows two jumpers. These jumpers are used to match the FSB (Front Side Bus) to that of the CPU. If these are set higher than that of the CPU, the computer may not start and will likely crash if it does start. For this CPU, the FSB is 166MHz. The rated FSB of the CPU is actually 333MHz. The FSB is doubled because we're using DDR (Double Data Rate) RAM.

Above, notice that we have two 3-pin headers and the left-most pin is marked '1'. Also notice that the jumpers are connected across pins 2 and 3. If you look at the table to the right of the jumpers, you can see that the configuration shown is for a 166MHz system.

At this point, the computer will power-up but it doesn't have an operating system so it will do little more. Next, I will go through the basic BIOS features then we will install the 'operating system', Windows XP.

 

 
 
 
 
 
 

If you have any suggestions for this page or for the computer pages in general, please Email me.
If you're interested in electronics or car audio, you may be interested in my car audio site. It has lots of graphics and covers virtually everything associated with car audio.
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Perry Babin 2005
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