The magazine of the Melbourne PC User Group
No Special Tools Required
John Mackesy
The old giant, IBM got it right first time, and everyone else followed the fashion they set. Today's personal computer - IBM invented that idea as well - is recognisably from the same stable as the first PCs, way back in 1981. Standardisation, that's the name of the game; it is standardised hardware and software that made possible today's huge PC industry - an industry that didn't even exist in 1980.
 
Until quite recently, today's PCs looked much like the clunky 1970s styled oatmeal coloured boxes that IBM used in the beginning. After all, these were products of International Business Machines, and they'd better look businesslike in the office environment, where even the clock you watched was likely to be an IBM product. Inside that box was something that looked very much like the contents of today's computer; a slide-in motherboard, bearing a number of plug-in cards, cards which fitted into standardised slots, a power supply, floppy disk drive and not much later, a hard disk drive. 		In March 2000, John Mackesy wrote an account of how he repaired and saved a broken 19 inch monitor from going to scrap. It demonstrated how someone with the right tools and a lot of experience in related fields can do such things. 
This time John shows us how easy it is to plug together the components of a PC and no doubt his words will ring true for many members. 
A little knowledge is very handy and you can gain that in so many ways. While this article is a good introduction, it is not the complete answer. If you are keen to learn more, the Hardware SIG would be an ideal next step - GT


Figure 1. Typical “D” Connector 
— male end depicted.


All these components were built to a standard pattern, as were all their electrical connections. Best of all, no special tools or significant expertise were required to completely assemble, add to, or disassemble the machine. Even better, when you put it back together, the probability was that it would work. When it came to connecting to the outside world, the compact and readily available "D" connector (Figure 1) was an inspired choice, a choice that has made it the standard connector of our time. IBM's history of keyboard manufacture ensured their keyboards would be the standard by which all others would be judged.

Today

Fast forward about 20 years - there has been a huge production of highly compatible computer equipment. Equipment that has become progressively cheaper, smaller, lighter, vastly more powerful, and regularly overtaken by advances in software. For better or for worse, the personal computer has become a fixture in the home as well as the office. Despite my having once said, like so many others: "There will never be a computer in my home", I joined the throng many years ago and have never looked back.

Where To From Here?

So much for history. Today's reality was that my aging 133 MHz Pentium with its 48 MB of memory was running out of puff and looking like it needed to be replaced by something with more sting. One of the major spurs to actually doing something about this was taking up the CD-R/RW offer organized for members by Melb PC last year. This device needed at least a 200 MHz processor to work. I tried, I really tried, but there was no way it would work with the 133 MHz equipment. Then there was the memory problem - my motherboard accepted only 72-pin SIMMs (Single Inline Memory Modules) (Figure 2) rather than the much more attractively priced 168-pin DIMMs (Dual Inline Memory Modules)


Figure 2. SIMM 
(Single Inline Memory Module)

The Solution

Having more pressing demands on my pathetically limited resources than investment in computing power I didn't really need, I began looking for a more potent successor to the Pentium. In practical terms this meant a later model ie. faster CPU (central processing unit) and the accompanying later model and faster motherboard to support it. The motherboard (Figure 3) issue was relatively easily solved - I had one laid on me. Although not exactly "bleeding edge" technology it represented a significant advance over the current equipment and it could accept both SIMMs and DIMMs. That was the good news - the bad news was that there was just an empty socket where the CPU plugged in.


Figure 3. The motherboard.

At least it was a "Socket 7", a standard and common feature. Eventually, I acquired a 300 MHz Cyrix 6X86M2 CPU, fallout from the liquidated assets of a recently defunct computer manufacturer. This was marked "faulty" but what the hell, why not give it a go? Another unknown was the condition of the motherboard. It would be nice to know if that was a goer before possibly lashing out real money on a CPU.

"Knowledge is Power" they say, so I downloaded a manual for the motherboard and data on the 6X86 processor. Like all motherboards, it had a part number printed on it; searching on that number quickly produced a PDF telling me everything I needed to know. The same process yielded a plethora of information on the 6X86, a device that turned out to have many more variations than expected. After I had ploughed through all this I had enough information to set up the various jumpers on the motherboard and move on to the next step. 

The Beast Lives

Testing time! Before I went any further, I needed to know if I had the basis of a working computer system or a component of the garbage stream. To find out, I assembled a "minimum configuration", test setup (Figure 4), just the bare minimum equipment to check motherboard functionality. This consisted of a video card, 16 MB memory, a keyboard, an elderly NEC SVGA monitor and a spare power supply; another refugee from the bin (repairing power supplies is a job for the dedicated technomasochist). Fingers crossed, power on. To my considerable surprise the thing worked, displaying video and memory information on the screen. As there was no cooling fan fitted to the 6X86 I switched off the system after a minute or so, to avoid overheating.


Figure 4. Assembling the minimum configuration 
for testing

Getting It All Together

Much encouraged, I fitted a temporary fan to the CPU, then attached a 3.5 inch FDD (floppy disk drive). After I set up the CMOS, the system booted from my Windows 98 startup disk. The next step was to fit an old 420 MB Conner HDD (hard disk drive); this was duly recognised by the system. So far so good. Using my Windows 98 startup disk I formatted the HDD and copied the operating system onto it. The machine booted up from the HDD, no problem.

By this time my project was beginning to look like a random collection of components interconnected by a forest of cables - but it at least it worked. I felt I was in with a chance. Expenditure so far? Zero!

A visit to the next computer market yielded 128 MB of memory ($35.00) and a proper cooling fan assembly with heat sink ($12.00). As the 6X86 dissipates about 25 watts of heat from a fairly small area, a decent fan is a must. To improve heat transfer between the CPU and the heat sink, I used colloidal copper paste. The system was then run for the next couple of days; no faults occurred. Things were looking good.

Assembly Details

So far, no tools have been used; everything just plugs together. Computer wiring falls generally into two categories - drive power connectors (Figure 5) and ribbon cables (Figure 6). Drive power connectors, 4 wires arranged red-black-black-yellow can only go in one way. You can't go wrong.
 
Ribbon cables are another story entirely. They have a coloured stripe (most often red) on one side, to assist with correct assembly. That coloured stripe goes onto pin 1 of whatever they connect to.


Figure 5. Power drive connector. 
They can only go in one way.


Figure 6. Ribbon cable.


Figure 7. Bed of nails connectors on the
 motherboard with Primary and 
Secondary IDE clearly marked.

 How do you find pin 1? That's simple - it will be marked near the motherboard "bed of nails" connector (Figure 7) and on the back of the FDD, HDD or CD-ROM drive unit. On HDDs or FDDs usually there is a small "1" near the row of terminals behind the drive connector, or on FDDs a small triangle near where the ribbon cable plugs in. I always draw a line on the back of the drive next to the "1" pin, using a felt tipped pen. The good news is if you get it wrong, no damage will occur - the drive just won't work.
 
One more thing. With FDDs most often the cable will have two connectors for two floppy drives. When you have only one FDD in your machine, connect that to the outer end of the cable, ie. the end with the twist (Figure 8). If there are two FDDs, connect the outer end to the drive you wish to be Drive A:.

With the AT style power supply to motherboard connectors - two flat plugs - the black wires go together in the middle (Figure 9). This is one best not to get wrong, as is the 240 V mains wiring to the power switch. 

Having proved to my satisfaction that the major components of the system worked, it was now time for a "dress rehearsal" - setting up the complete system outside the case. It's much easier to troubleshoot when everything is arrayed before you, naked and unashamed.

Configuration
 
First, some configuration decisions. As is typical of most PCs there are two IDE (Integrated Device Electronics) ports on this motherboard. They connect to the Primary and Secondary controllers which control the attached IDE devices (typically things like HDDs and CD-ROM drives).

Each controller (primary and secondary) can handle two devices, daisy chained on one cable. On each of those cables one device is known as the Master, the other is the Slave. So, if you had four IDE devices, (say) two HDDs and two CD-ROM drive units, you would have:
  • Primary Master
  • Primary Slave
  • Secondary Master
  • Secondary Slave
a nd usually the drive letter of a device is decided by where you connect that device. Typically the Primary Master is Drive C:. The others can be placed where desired and that alone is the subject of another article. Many newer IDE devices are capable of configuration by jumper settings on the device itself, others rely upon the device being attached to the appropriate port (connector).


Figure 8. Floppy drive cable. Note the 
twist indicating the end where you 
plug in your Drive A:.


Figure 9. Connect the power leads 
to the motherboard with the black 
wires in the middle.

In this computer the Quantum Fireball HDD, carried over from the previous system is connected to IDE port 1 (primary) and set as the master. It is drive C:.

The LG CDR/RW drive is set as the slave on the primary controller - Drive D:

The Sony CD-ROM is the master on the secondary controller - Drive E:

There is no slave on the secondary controller.

The 3.5 inch FDD to floppy port, Drive A: (There is no drive B:)

It is often suggested that having a HDD and a CD-ROM drive on the same controller is not a good idea, transfer rate being adversely affected, but I haven't noticed any problems so far. Investigation continues in this direction.

CPU Fan

The CPU fan came with a 3-way plug and a 30 cm cable. The motherboard had a 2-pin fan socket, 3 cm from the CPU, so the cable was shortened and the 3-way plug replaced with a 2-way plug. Like many newer fans this one has a tachometer pulse output (yellow wire) not used in this application. Some later computers use this pulse output, proportional to fan RPM, to provide control and indication of fan speed. It's not necessary to the operation of the fan.

Final Checks

Next, I fitted the Netcomm internal modem card, Trident Blade video card, Soundblaster and Network cards from my previous system, arranged everything neatly and safely, connected all the cabling, the monitor, the keyboard and the mouse, double checked everything, and switched on.

Perfect! Worked like dream; much like before only noticeably quicker.
 
Inspired, I had a go at burning a CD-ROM; good result first try. There was a minor conflict issue involving the Network card's IRQ assignment, readily resolved by disabling the unused IDE port on the sound card. In practice this didn't seem to cause any problems and was only found while checking each device through the Windows Settings | Control Panel | Device Manager | Properties.
 
Packaging - The Box It Goes In

Although a computer system resembling an electronic scrap yard has a certain deviant "differentness", practicality demands that it be decently housed. "The box it goes in" is a rather personal issue, but the choice basically divides along two lines. The desktop case (you can put the monitor on top of it) and the tower case, which goes somewhere out of the way. Supporting a 31 Kg 19' monitor is a bit beyond most desktop cases, so I opted to stay with my previous case, something best described as a "squat tower". Circa 1990, this is a rather odd looking semi-industrial creation, all metal and built to a high standard. 

As I said earlier, choice of case is a very much a matter of individual taste, but there is one thing to avoid at all costs - cases with sharp internal edges. Unbroken metal edges can be razor sharp. I still have the scars.

To get everything in the box, the system had to be taken apart (again) and reassembled in its new home. I put the plastic standoffs (Figure 10) on the motherboard, and leaving the drive cables and the DIMM on the board, lowered it into its mounting slots, then fitted the two securing screws. Leaving the cables connected is much easier than trying to work in the dark and confined space inside the case. 

It is worth noting that the dimensions and mounting system are all the same as an early 1980s XT. IBM definitely got it right.


Figure 10. The plastic standoffs used to mount the motherboard on the base of the case.

Mechanical Assembly

Next, the mechanical details. The HDD (designed for a 3.5 inch bay) is mounted in an internal 5.25 inch bay, with a 3.5 to 5.25 adapter kit. The CDR/RW drive is mounted directly above that, then the CD-ROM drive and above that the FDD (Figure 11). Drive mounting screws should not exceed a maximum length of 5 mm. Any longer than that and you might damage the drive's internals.
 
After the drives were mounted, I connected their ribbon cables, then the serial and parallel port cables to the appropriate "bed of nails" connectors. Power supply next, motherboard connectors (black wires to the middle) attached. Then I attached the power supply to case. It has four screws.


Figure 11. Mechanical Assembly.

Then I plugged in all the drive power plugs and connected the four wires to the push button power switch.

A good manual is important for almost any task but when connecting the various wires to a motherboard a manual identifying the various connections is imperative. I hooked up the speaker, key lock, reset button and the HDD indicator LED. Then the sound card, Network card, video card, modem - oops, I had forgotten the wire between the sound card and the CD-ROM. All this might seem like a lot of work, but it doesn't take long and requires no tools other than a Phillips screwdriver and a pair of needle-nose pliers, and of course, that manual identifying the various connectors.

In Service
 
That's it, I was all finished and ready to go. I'd like to say there weren't any later problems, but that isn't strictly true. Although everything worked just fine, cooling was an issue. This was largely due to the power supply and fan being mounted at the bottom of the case (see front cover image). When you consider that hot air rises this seems like a crazy idea. What made things worse was using a power supply with a temperature sensing fan. The sensor never got the message.
 
While no operational problems resulted in the short term, the case was getting quite warm, so I fitted a standard power supply with a continuously running fan.

As I said earlier, this system is not latest technology - but it's an affordable answer to my needs and it is 100% reliable. Nothing but the most basic tools were required, no special skills were needed, and my faithful Aussie card table was the perfect workbench.

You too, can build your own computer.

Reprinted from the March 2002 issue of PC Update, the magazine of Melbourne PC User Group, Australia