Step By Step 6 - Installing a new motherboard

Originally published in Australian Personal Computer Magazine, April 1998.
Last modified 03-Dec-2011.


Want a new motherboard? Want to install it yourself? Scared to death of all those cables?

Read on.

Get the specs

Before you even open the computer's case, make a note of the IRQ and DMA and I/O address settings of everything in it. If you're running Windows 95 or 98 and have a printer, this is easy enough - open System Properties in Control Panel, click the Device Manager tab and click Print. You will now have a few handy pages telling you what's where.

It used to be essential to now reset the machine and hit Delete for the CMOS setup menu, then write down the hard disk heads, cylinders and sectors. It's almost certain that you'll be able to auto-detect the hard drive parameters with the any remotely recent board and drive, though, so this step is now one for the paranoid.

Take it to bits

Now, rip the machine apart. Leave the power supply plugged in but turned off, so the case metalwork will be at mains earth potential, for the lowest chance of electrostatic discharge problems. Touch said metalwork before your fingers stray near a chip, and touch it again if you move away from the machine and back. As a reader pointed out the last time I mentioned this strategy, if the power supply unit (PSU) or power point is disastrously miswired, this can be dangerous. Such a problem should be evident earlier, though, since brushing against a machine with a live-chassis fault will probably cause you to punch yourself in the head and fall down.

Opening the case shouldn't slow down anyone with a screwdriver, despite the multiplicity of case designs out there. Removing all of the cards should also be no big deal. Which gets us to the motherboard.

Here, there are a lot of connectors to deal with. Take note of the orientation of the connectors - ribbon cables can be "keyed" to only plug in one way, but if the connector and header are unkeyed, it's possible to connect things backwards. The stripe on the ribbon cable indicates the side of the connector with Pin 1, and Pin 1 should be indicated (in tiny type) on every header.

Pay attention to your floppy drive cable - it will have an end that connects to the floppy controller header on the motherboard, and two drive connectors. The PC assigns floppy drive identities according to which of the two drive connectors you use - the A: drive connector is the one at the end of the cable, after the split section where part of the cable has a half-twist, and the B: drive connector is the other one. It doesn't matter what connector you use on an IDE or SCSI hard disk controller cable, but it does matter for the floppy drive.

Better cases have labelled connectors for all of those little non-obvious buttons and lights. Lousier cases do not. If you have one of the lousier cases, sticky tags or scribbled notes or some such memory aid will make reattaching all of the wires simpler.

Actually removing the motherboard may require you to detach some more metalwork, usually a hard and/or floppy drive mounting cage. Thanks to the abovementioned plethora of case designs, getting access to the motherboard has to be left as an exercise for the reader.

Power supplies

This is as good a point as any to talk about power supply units (PSUs). The basic design of older PC PSUs dates back to the IBM AT, and they're referred to as "AT" PSUs. The AT PSU has a two-part power connector, which plugs into a long socket on the motherboard. Each half of the connector only connects one way without serious breakage, but it's possible to assemble the two plugs the wrong way around, with the left half on the right and vice versa. This is A Bad Thing. Just remember that the black wires go in the middle, like so:

atpower.JPG (10136 bytes)

If you've got a newer PSU, it should be of the "ATX" variety. ATX power supplies don't have a switch on the PSU box - they have a line on their connector to the motherboard which, when switched, turns them on. They can also be turned off by software - if your Windows computer turns itself off when shut down, that's an ATX PSU at work.

On the plus side, the ATX PSU's sensible one part power connector means amateurs no longer wince the first time they turn on their newly assembled machine. On the minus side, an incorrectly assembled or configured ATX system can behave in mystifying ways. If the motherboard has, for example, not yet had its BIOS set up properly for the CPU yet has its "CPU Setup" jumper set in the normal operation position, the machine may obstinately refuse to power up. Likewise, some motherboards may not let you power up if you haven't yet connected a hard drive, so an old-style minimal-system configuration test is impossible.

Jumper setup

Before you put the new motherboard in the case, install the CPU and set the bus speed and multiplier jumpers, if your motherboard has them, according to the instructions in the motherboard manual for the CPU you've chosen. A properly grounded antistatic mat is the best surface to put the motherboard on while you work on it, but in the real world old newspaper is adequate. Touch metalwork on the PC case and you should be close enough to the ground potential of the motherboard not to fry anything.

If your case design makes it difficult to install RAM SIMMs or DIMMs when the motherboard is screwed into place - and what used to be easy might be hard with a differently laid out motherboard - then now is not a bad time to install your RAM on the new board. Bear in mind, though, that this makes the RAM more vulnerable to static or (more likely) brute mechanical damage during the rest of the installation procedure.

Motherboards attach to cases with two flavours of fastener - brass spacers and screws, and plastic spacers. The plastic spacers push through holes in the board and click into place, and their stepped bases slide into keyed slots in the case. They're very sloppy, though, so you need the metal hardware to hold the board firmly in place.

Put your new motherboard roughly where the old board was, making sure it's orientated the right way, and see what holes in the board line up with what holes in the case. If all of the board holes line up with a hole in the case you'll be eligible for a special medal, but there should be a good selection of holdfast locations that match.

Any brass spacers that match up with a motherboard hole can be left in place; any that don't will have to be moved until they do. The brass spacers are hexagonal and can be removed and replaced with a 3/16" (near enough to 5mm) wrench or nut driver.

Get the plastic spacers out of the old board by pinching their pop-out tops with pliers, and pop them into the holes in the new board that line up with the key-slots in the case. Now put the motherboard back into the case, and wiggle the plastic spacers through the large end of their case slots.

Once all of the plastic spacers are located in their holes, slide the motherboard so the brass spacers line up with their board holes. Using the screws and washers from the old board, firmly affix the motherboard to the brass spacers.

The purpose of all of these spacers and screws is to stop the motherboard moving around, and, very importantly, to stop the zillions of uninsulated solder pads on the back of the board from shorting out on the case. If this happens - and it can, if a board is inadequately supported and/or bent by a badly installed card - the results can vary from unpredictable resets to utter destruction of expensive components.

Now you should install your CPU (if you haven't already) and RAM. Modern easy-insertion sockets make CPU installation a drop-in procedure, and snapping SIMMs or DIMMs into place is also easy enough, provided there's no metalwork in the way.

The smoke test!

Now it's time to attach the cables and do power-up test. Connect the power supply. Connect the reset switch, power light, hard disk light, and serial, parallel, hard and floppy drive ribbon cables, and the CD-ROM cable if your CD-ROM drive runs from the motherboard IDE controller. The connectors on any decent motherboard are labelled, and the motherboard manual should have a map of all of the connectors and jumpers too, so it's no big deal to get the serial ports the right way around and the reset switch connected to the right couple of pins. If you get connectors backwards, things won't work but also won't explode. It's only AT PSU connectors that can toast a board if done wrong.

Make sure your CPU cooling fan has power - there should be a two or three wire lead that goes to the motherboard or a passthrough arrangement for a power supply connector.

Don't put all of your cards back in; all you need is the video card. Plug in the monitor and the keyboard. Look carefully to make sure no screws, spacers or other conductive mischief-makers are sitting on the motherboard. Power up.

Assuming nothing smokes, set up the BIOS data. Auto-detect the hard drive, and make sure your machine knows what kind and number of floppy drives it has. If you've got a spiffy software-setup motherboard, this is where you set your CPU speed as well. Fix the clock time if it's wrong, leave the million and three other settings alone, save your changes and turn the machine off again.

Install the rest of your cards. Hook up the CD-ROM audio cable to the sound card, and its controller ribbon cable as well if your CD-ROM doesn't run from the motherboard IDE controller. Screw the cards in. Do not put the case back together. Power up again.

This is where your Windows configuration printout will come in handy, if of course you're using Windows. The computer's brain transplant will give it multiple conniptions over its setup, and you can expect to do a lot of hardware-detecting and resetting. Refer to the printout for your non-Plug and Play hardware, and bear in mind that Plug and Play components may have changed settings. Most machines sort themselves out without too much fuss, but intractable problems may require you to remove cards, set up what remains, then replace them. For more information on fixing Plug and Play problems, check out my second Step By Step column, here.


And that, with luck, is it - with one more note. If you're one of the rugged individualists who runs Linux, changing the motherboard may cause the machine to freeze on startup with the letters "LI" on the screen. This is LILO's fault. To fix it, boot DOS and rewrite your master boot record by typing


and then use your Linux boot disk to reload Linux and reinstall LILO.


More info

For a lot more information on constructing your own computer, check out my big tutorial on the subject here.


DMA: Direct Memory Access, the act of directly moving data from a device to memory without passing it through the processor. DMA is often used as shorthand for "DMA address", one of the limited resources of IBM compatible computers. See my second Step By Step column for more information.

IRQ: Interrupt ReQuests are how IBM-compatible computers assign the CPU's attention to devices that need to talk to it right now. A device gets assigned a given IRQ and uses it whenever CPU time is required; if two devices have the same IRQ and try to use it at once, neither will work. Current PCs have 16 IRQ lines, but several of them are taken up by standard hardware. See my second Step By Step column for more information.

I/O address: I/O addresses, also referred to as "I/O ports" or "port addresses" are what a CPU uses to tell which of its peripherals is presently clamouring for its attention. If two devices are set to use the same I/O addresses, it's likely that neither will work. See my second Step By Step column for more information.

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