Taking Apart A Computer

Taking Apart A Computer - Putting It Back Together

Isn't that the most paradoxical title ever? After totally disassembling the computer, we're going to finish taking it apart by putting it back together. Oh well, it sounded good when we first thought of it.

Whimsical titles aside, this lesson will teach you more than just how to build a computer. Every time you install something into a computer, you'll use this lesson. So... To make our title seem more ironic, there's more to putting together a computer than putting together a computer, for the purposes of this lesson anyways. (Confused yet?)

FRU's

One of the major distinctions you'll have to make is when a unit is Field-Replaceable and when it's not. Field-Replaceable Units (FRUs) are components that can be changed at the customer's site. Non-FRUs are components that must be taken back with you to be repaired. For example, a video card is an FRU because it can be easily replaced on site, where a laser printer is non-FRU because they generally have to be repaired in-shop. Not very practical in the field any more as 95% of the components are FRUs and the remaining 5% is made up of stuff you normally ship back to the factory to be repaired.

Getting It Straight

The hardest part of reassembling the computer is going to be getting the motherboard in. In most cases it's dependant on the form-factor and the type of motherboard it is how it's going to fit. Here's our rough step-by-step guidelines for installing a motherboard;

If you haven't already, take out the back metal panel from the case that the motherboard attaches to. It will come off somehow, but varies by case. If it's a desktop case, just skip to step 2.
Lay the motherboard on top of the metal panel with the edges of the motherboard facing the directions that the metal panel will connect to in the case. For example, the serial ports should be facing the back of the case, as should the USB and mouse/keyboard ports.
Look closely through the holes in the motherboard. You should see some that match up to small threaded holes, and some that match up to bigger non-threaded holes. Remember which go where.
Everywhere that a threaded hole matched up, place a threaded standoff. Screw it in tight. Where there were big holes, place one of the nylon/plastic standoffs that pop into the motherboard.
Slide the motherboard so the plastic standoffs catch in their holes. Line up the threaded standoffs, making sure you have a paper washer in between the motherboard and the standoff. Put a screw with a washer on it through the hole into the standoff and tighten it down.

This SHOULD anchor your motherboard in position. Look underneath the motherboard to make sure that it's not making contact with the metal panel. If the motherboard is touching, clip the bottom end off a standoff (The part that would hook into the metal panel) and push it through one of the extra holes in the motherboard. It should help keep corners elevated and avoid shorting it out. You can't go wrong with too many standoffs supporting the board. (You didn't think those extra holes were going to go to waste, did you?)

The Brains Of The Operation

Next comes the CPU and memory. Seeing as we were smart enough to care for our CPU, simply line up the pins so that the CPU faces the direction it states and push it lightly into place. ZIF socket processors shouldn't require any force, and PGA sockets only require slight force. Don't push too hard, because (as we learned last week) processors can't be fixed once they're broken.

Try snapping in the heat sink and fan system now. This can be an arduous task, as some require the brain of a rocket scientist, the flexibility of a gymnast, and the patience of a Pope to install. Read the instructions carefully, as each heat sink/fan system seems to have it's own method of installing. Make sure that if your processor requires thermal cooling grease that you smear it on prior to putting on the heat sink. (Why go through the whole heat sink dilemma twice, right?) If you forgot, don't try squeezing it in. It won't work. You have to coat the top in order to get it to work properly. Make sure that you hook up the power connectors to the motherboard from the heat sink, or the fan won't turn. (and your computer won't work for very long)

Seeing as the motherboard/metal panel are still out of the case, we might as well add the memory back in now too. All memory is idiot-proof, meaning it is notched so it only fits in one direction. (We're not calling you an idiot... honest.) SIMM's get inserted at a 45 degree angle and pushed back until they snap in place. DIMM's are pushed down until the plastic clasps on the side lock in place. If the RAM doesn't seem to sit right, make sure you have it in the right direction and there isn't anything interfering with it's contacts.

Wiring It Up

It's time to place the metal panel with our motherboard/CPU/memory back into the case. If you figured out how to get that back panel out, it should go in pretty much the opposite way. Now look for the big wiring harness from the power supply. If it's an ATX case, there should be 1 wiring harness with 20 wires. If it's AT, there should be 2 wiring harnesses with 9 wires each. Snap these into place. ATX harnesses are notched (AKA idiot-proof) and AT connectors only fit one way into the slots. (Make sure the black wires in each connector on an AT harness are beside each other. This is the proper position.)

Next go to that diagram we made of the wire pins that connect the motherboard to the speaker, case, and power supply. If it's a new motherboard, examine the instruction booklet. Put each wire back in it's original place in it's original direction. Some of these wires are polarized, some aren't. If you put the speaker connector on backwards you probably won't notice the difference. Put the reset switch in backwards and the computer may not boot. Carefully examine each connector before installing it.

(Note - For some reason, case manufacturers and motherboard makers haven't agreed on the right way to label those connectors. Even though a Pentium-class computer doesn't use a Turbo button, most cases still have this connector. The only real important ones are the speaker, the reset button, and the LEDs for the front of the case. Everything else will most likely function without being connected.)

Driving It Home

Now you can put back in all the hard drives, floppy drivers, and CD drives you so patiently removed last time. Make sure you replace all the screws that you took out last time (I actually felt guilty and put in a second screw into my hard drive after last week's lesson.) and make sure that CD and floppy drives are flush with the front of the case. Connect the ribbon cables from the motherboard to each drive, remembering that hard drive cables are notched and floppy drive cables aren't. You can't put a hard drive cable on backwards very easily, but backwards floppy cables are a common habit. If you get screwed up, just remember that the red wire on the ribbon is wire #1, which lines up to pin 1 on the connector of the drive AND the motherboard. All motherboards and drives come with pin 1 marked, and all cables come with the first wire red. There are no exceptions.

Plan how you connect your drives carefully. If you connect a hard drive and a CD drive together, the slowest of the two will mandate the transfer speed. A 7200 RPM hard drive that works in ATA 100 will only transfer at the speed of the CD drive, which could be 1/10th of the speed. Normally you would connect hard drives on the primary IDE channel, and CD drives on the secondary.

Another consideration is multiple ATA66/100 drives. If you connect these devices, you must use the special 80 wire connector labeled ATA66/100. These connectors are also specially wired, so that they have master and slave connectors. If you connect a master drive to the slave connection on an ATA 100 cable, the drive won't work.

After you're done hooking up ribbon cable, attach a power connector to each drive. Remember that a 3 1/2" floppy drive uses the smaller power connector. You also have to connect the Audio cable from the CD drive to the sound card.

Lastly, put all the adaptor cards you took out back in, preferably in the same slots. There's no magic system here. Just push them down and screw them in. Wire up your power, mouse, keyboard, and other connectors and you're ready to go.