Making Your Own Ribbon Cable

PURPOSE

This document will teach you how to make your own ribbon cables to connect your hard disks and floppy disks to the controller. It will also try to persuade you that doing so is a good thing.

I will be using non-technical language. I presume those who need learn this skill would be frightened off by a technical discussion. I also presume those who know the technical language also know how to make cables already. I hope this will be simple enough that ANYONE can now make their own cables.

THE PROBLEM

Most clones use prefabricated gray ribbon cables from Taiwan. These are of low quality. I find cables are to blame in a surprisingly high percentage of supposed "disk" failures.

Here are the problems you will encounter:

1. Poor quality contacts tarnish and you get intermittent hard disk and floppy errors.

2. Cables do not flex well and kink when forced around corners. You get temperature sensitive intermittent floppy errors as wires make and break contact.

3. The contacts have weak springs in them. The cables gradually wiggle off, especially when you transport your computer in a car. If you service your computer, each time to remove and restore the cables, the springs get weaker still.

4. The cables usually are longer than necessary. The excess cable retards air flow, messes up the innards, and acts as an antenna attracting noise to interfere with the delicate signals travelling from your disks to your controller.

5. The cables sometimes are too short. This limits your slot choice or means straining the cables -- which mean they will eventually pull off.

6. The cables have many 180 degree twists in them to allow for the way the various devices are mounted. These twists eventually kink the cables. The twists are unnecessary when you custom-design your cables.

7. Your disk fails. You buy a new one. However, your old one would have worked just fine had you cleaned the contacts and installed new cables.

THE SOLUTION

Make your own ribbon cables with high quality flexible ribbon cable, using American-made gold-plated connectors with super strong springs. Treat the contacts with Stabilant -- a semi- conductor gel that bridges any small gaps at the contact.

THE TOOLS

If you want to make hundreds of cables a day, you could buy a $1000 crimping tool with a set of dies for the various connectors. However I will presume you just want to make a few cables. For that all you need are:

1. Fluorescent-pink translucent plastic triangle. Get this at an artists' supply store or an art supply house. You need a straight edge and a right angle. (It does not have to be pink, but it helps if it is translucent. The colour makes it easier to find in a crowded workshop.)

2. Pair of scissors.

3. Exacto knife -- a handle that holds a rigid razor blade like knife.

4. a vise. I have heard rumour you can close the connectors with a mallet, but that is not my style.

5. A small block of wood to act as a cutting board.

THE CABLE

I like 3M brand Spectra Strip ribbon cable. It is rainbow coloured which I find makes it much easier to use, especially when it comes time to count the conductors to make twisted floppy cables. When they are all gray, my eyes just give up.

For each computer you will usually be building three cables. You need some 34 conductor cable (for the floppy cable, and the wide hard disk cable) and some 20 conductor cable for the narrow hard disk cable. If you are buying just enough for one set of cables, buy three times too much to give yourself a chance to goof up. By Murphy's law you will get it right the first time.

Buy plain flat cable. The braided stuff will be harder to handle. Take a sample set of cables with you when you go to buy the parts. It is quite legit to just point and say -- I want some of that only in rainbow colours and more flexible.

THE CABLES

The cables we will make look like this:

ctrlr:pin ------------B:edge-X-A:edge 34-conductor wide floppy cable

ctrlr:pin ---------------------C:edge 34-conductor wide hard disk ctrlr:pin ---------------------C:edge 20-conductor narrow hard disk

ctrlr:pin -----------D:edge----C:edge 34-conductor dual hard disk ctrlr:pin ---------------------D:edge 20-conductor narrow hard disk

THE CONNECTORS

For an A: B: floppy cable, you will also need a two 34-pin edge connectors, and one 34-pin pin connector. For a CK-17 type cable that gives A: B: and mag tape, you need a third 34-pin edge connector.

For a simple hard disk cable you need a 34-pin edge connector and one 34-pin pin connector for the wide cable. You need a 20-pin edge connector and a 20-pin pin connector for the narrow cable.

If you want to support two hard drives, you will need two 34-pin edge connectors and one 34-pin pin connector for the wide cable. You need a total of two 20-pin edge connectors and two 20-pin pin connectors to make the pair of narrow cables.

I have had success with Amphenol and RN brand. You want ones with some gold plate -- that is the reason we are going through this exercise -- to get good contacts.

Your best bet is to take in a Taiwanese floppy cable to show the electronics clerk the sort of ribbon cable you want, and the sort of connectors you want.

There are hundreds of variants. So long as it looks mechanically the same dimensions, you are ok. Some people think strain relief is a good idea. You make the cable go through a few loops before exiting the connector so it cannot pull out. These are harder to make, are bulkier and might not fit in between boards. You have greater danger of kink damage. Since there are no forces pulling inside the machine, I don't use these myself, though others have recommended them.

THE CABLE COLOUR CODE

The colours of the ribbon cable conductors follow the resistor code, except they start counting with 1 (brown) instead of 0 (black).

# Colour Tradition Proper

0 Black Bad Bad
1 Brown Boys Boys
2 Red Rape Ride
3 Orange Our On
4 Yellow Young Young
5 Green Girls Girls'
6 Blue But Bicycles.
7 Violet Violet Violet's
8 Gray Goes Got
9 White Willingly Wrecked

A floppy cable has 34 conductors, so it starts with brown for pin 1, red, ... gray, white, black, brown, red ... repeating itself and ending on yellow. (See the figure near the end of this document.) The narrow hard disk cable has only 20 conductors so it starts at brown for pin 1 and cycles ending up on black.

If you bought cheap cable, it will all be gray, except pin 1 will have a red or blue stripe.

PLANNING YOUR CABLES

It is best to start with a machine with cables already installed. Before you remove them, note very carefully how they were attached. You can use these old cables as models for making new improved ones.

Brown is pin 1. It is very important that the brown conductor goes to pin 1 on the controller card, pin 1 on the hard disk connector, and pin 1 on the floppy connector.

How do you tell which is pin 1? It might even be marked! There might be a dot near it. There might be a notch bitten out near it. There might be a pin broken off near it. When you find it, mark it with a red Sharpie permanent marker (NOT on the contact itself, however!)

Drape a loose piece of cable in your machine twisting it minimally so that pin 1 of the cable visits the necessary pin 1 points in the machine.

Let us start with the narrow hard disk cable -- the simplest. Lay a piece of cable out in front of you (don't cut it yet) with the brown pin-1 stripe a way from you like this:

---------brown---------
-----------------------
-----------------------
-----------------------

Imagine we are going to attach the pin connector to the controller on the left hand end. There are four ways you can attach it. Two have the connector pin holes down, two up. You can attach it right side up or upside down. Strangely, all four ways could work, but there are two "confusing" ways, and one "best" way.

If you look closely at the connector, it may have pin 1 of the connector marked. It is almost symmetrical, so the choice is in a sense arbitrary. It may be a dot, or a small 1. You want to make sure that pin 1 of the connector goes to pin 1 of the cable. Otherwise, someone who does not know that brown=pin1 might read the number and hook the cable up incorrectly. When you find pin 1, mark it with a red dot.

Ok, that rules out two possibilities, and leaves two. Even with pin 1 against the brown, you can still have the connector pin holes facing up or down.

This is why you draped your cable. One way will let the cable drape naturally. The other will create a 180 degree loop. I prefer natural drape since the cables take less room, kink less, and interfere with air flow the least.

Now repeat the planning for your edge connector that attaches to the hard disk. You can have the cable flow out the top or bottom of the disk, and still have pin 1 attach to pin 1. It is easier to attach and remove hard disk cables in tight quarters if they flow out the top of the disk.

Make a mockup of your new cable with paper or using an old Taiwanese cable, showing where you would reverse and where you would leave connector the same.

CHOOSING THE LENGTH

If you have trouble with choosing your cable lengths, ask Goldilocks to help. If you make them too long, they tangle, impede air flow, kink, and look messy. Part of the reason for this whole exercise was to shorten the cables to reduce the antenna effect, so don't blow it with whang dang doodle cables. IDE and RLL cables especially should be kept as short as possible.

If you make them too short, they won't reach and you have to make new ones. Also you have no flexibility to move things around a little. So, to start, err on the long side. As you gain experience, you can cut the tolerances tighter.

CUTTING THE CABLE

Use the triangle to mark a right angle across the cable. Score it with the Exacto knife. You can then repeat the scoring till it cuts through. I find repeated scorings work better than one big one since it stretches the cable out of square less. Or you can finish the job with scissors. Try both ways to see which gives a cleaner, squarer cut. It will depend on your tools and your mechanical skills.

THREADING THE CONNECTOR

Then thread the cable through the pin connector on one end. Triple check you have threaded it in the way you planned. You have only one chance in four of getting right if you just do it randomly. You will see two rows of teeth. The wires slide between the teeth like 34 little pieces of dental floss. There are a pair of teeth reserved for each wire. You have to get each wire paired up with correct set of teeth. This is much easier than it sounds.

Align the cable, check both the front and back row of teeth for perfect alignment. Especially check the two outside conductors on each side. If you get them right, the rest take care of themselves.

LOCKING THE CONNECTOR

Get out your triangle and make sure the connector is perfectly square with the cable. Now gently squeeze the connector shut. A bar will force the wires into the crevices between the teeth. They won't go in, unless your name is Clark Kent. Now gingerly put the thing in a vise, never letting go. Keep watching to make sure it is still square. Use the vise to squeeze one end a little, then without letting off the pressure squeeze the other end a little. If all is still square you can manipulate the whole thing in the vise at once. This is very hard to do without the preliminary mini-squeezes on the ends. Screw down, holding the cable out the way so you can watch the wires being tortured and impaled on the teeth. When they are fully down, you might hear a tiny click as the connector locks. Don't squeeze further, or you will just crack the connector.

Remove it from the vise and study both sides. It should still be square, and all the teeth should be attacking the correct wire. The teeth have sharp sides that bite through the insulation of the wires.

TOUCH UP

If you were very careful inserting the cable in the connector, there will be no cable poking out the other side, and there will be a perfectly smooth end. However the stub should poke out enough to clear the teeth.

What if your cable has a ragged end poking out? Just use your Exacto knife to pare it off. Be VERY careful. Connectors have a nasty habit of suddenly twisting in your hand and you stab yourself with the Exacto knife. (How do I know these things?)

ATTACHING THE 20-PIN EDGE CONNECTOR

Then put the other end edge connector on and repeat. I always start with the pin connector instead of the edge connector, because they are cheaper. In learning, I like to destroy cheap stuff first. Again triple check your design with your plan before you start squeezing. If you do it randomly, you have only one chance in 16 of getting a two-connector cable right.

THE WIDE CABLE

The wide hard disk cable is only slightly tougher because there are 34 wires to impale between the teeth instead of 20.

Just repeat as for the narrow cable, but use 34-conductor cable an 34-conductor connectors.

DUAL HARD DRIVE CABLE

Unless you have two physical hard drives C: and D: you can skip this section. If you have one drive, split into C: and D: partitions, you can also skip this section. However if you have TWO physical drives, you HAVE to read this confusing stuff.

If you need to support two hard drives, you will need TWO edge connectors. One goes in the middle of the cable. You must build the cable in this order:

1. pin connector for controller

2. edge connector for D: drive in the MIDDLE of the cable.

3. edge connector for the C: drive on the END of the cable.

If you did the C: connector first, you would find you could not thread the D: connector on it because the C: connector would block you.

If you use two hard drives, strap your C: drive as DS0 and your D: drive as DS1. Unfortunately some disk manufacturers start counting at 1. If you have one of those drives, use DS1 and DS2 respectively instead. For more detail on installing dual hard drives read my essay DUAL.DOC.

If you use two hard drives, put a terminating resistor in your C: drive (the default) but remove it from your D: drive.

Note this hard drive cable for dual drives has no twists in the conductors. My scheme avoids those monstrosities. However there are many ways to skin a hawk. There exist variants with C: and D: reversed and twisted cables. I believe the method I have shown here is the most reliable and straightforward.

FLOPPY DRIVE CABLE

I have saved the worst for last. These wretched floppy cables have a deliberate TWIST inside the cable! I worked all night once trying to find a way to avoid this ugly, reliability- wrecking twist, but finally convinced myself that IBM has meddled with Shugart's design of the floppy disk controller interface so badly, it was not feasible. The twist requires some manual dexterity to master.

You can make new hard drive cables, and leave your floppy drive cable as its crummy old original if this daunts you too much.

The rationalization for it is the twist means you don't have to set the drive select jumper on your B: drive, just remove the terminating resistors.

Prepare the pin end connector to the controller and the middle B: floppy drive edge connector just as you would a dual hard disk cable. (Oh, well you did have to read it anyway.) We have to then introduce a twist between the B: and A: connectors.

I suggest you study a working floppy cable to see how this works. 3D effects are hard to show in vanilla ASCII text.

Hooking up the final A: connector is tricky. You have three flaps of cable to thread and align. You also have the twist fighting you. It wants to drag the middle tongue out of alignment. Since the middle flap has a twist, it is a tad shorter that the outside flaps. So in your aligning, let the outer flaps poke out more. You can trim them all off neatly later. Be ULTRA careful that all three flaps are perfectly square and all conductors are meshing with the right teeth. It might help to borrow someone's extra pair of hands for this tricky task.

TREATING

I swab a few drops of Stabilant 22A into the contacts of all female connectors. I clean all male connectors with Cramolin, rinse with isopropanol and swab on Stabilant to finish. This treatment keeps your contacts from tarnishing and forgives any poor mechanical contacts.

TESTING YOUR CABLES

Recheck your cables with your plan. If some connectors are not on squarely, start over. Unfortunately, recycling the connectors is often very difficult. Compare your cables with known working cables. Study them for signs of malocclusion.

Now try them out. You cable will not be keyed, so it is possible to put them on upside down. Make sure all power is off when adjusting or changing cables. Make sure the brown conductor goes to pin 1 of each connection.

The wide hard drive cable visits both hard drives if you have two. C: is on the end. The wide floppy cable visits both floppy drives with A: on the end. There is a separate narrow cable for each hard drive.

The connectors on the hard/floppy drive controller are traditionally laid out like this, but don't count on it:

narrow  narrow    wide       wide
D:      C:      C:/D:      A:/B:

This sounds much more complicated than it is. You can do it much faster than I can describe it. Consider that I am one of the most mechanically inept people around. I make cables successfully all the time. I give so much detailed advise, because I imagine I am talking with someone like myself with little mechanical intuition.

Basically all you do is cut your cable squarely, thread the connectors squarely, and squeeze.

DISCUSSION

Information I would like to add are mail order sources and costs for small quantities of the various materials. If you have that sort of info, please post. As always all feedback is much appreciated. I built my first cable less than a year ago, so I can't call myself an expert.