Cable Repair

Last month, we left off covering basic soldering techniques. Now we’ll move on to instrument cable repair, an exercise you can use to practice your new soldering skills.

An instrument cable will have one insulated wire in the center which is connected to the short center terminal and connects to the “tip” of the plug. A mesh of fine wire surrounds this center wire. This wire will be bunched up and soldered to the longer terminal, which connects to the “sleeve” of the plug. The center wire carries the signal; the fine wire mesh acts as a shield against outside interference such as radio waves and other noises. One way to check if a cable is broken is to unscrew the rear housing of the plug at each end and look for breaks. Another is to place the probes of your multi-meter on the tip or sleeve of each end of the cable and check for continuity. You can set your meter to its lowest ohm/Ω setting and look for .1 to .5 ohms on the screen. If the screen shows no ohm reading at all then you probably have a break.

1. Since most cables break at the solder joints or near one end — where they receive the most wear and tear — I’d suggest cutting off about six inches of cable from the end you have determined is broken.

2. If the plug looks salvageable, disassemble it and put the rear housing and the plastic tube insulator back on to the cable that you will be using. This is important! I have very often had to perform this repair twice because of this easy mistake. Cut away the leftover cable from the plug and mount it in a vise or alligator clip stand. Remove the leftover solder and pieces of cable with your iron and solder braid.

3. With a utility knife or wire strippers, strip back the outside rubber insulator of your cable - about half an inch.

4. Here you will see the braided wire shield. Bunch and twist this up into one wire as best you can. Then strip back the insulation off the center wire about a 1/4 of an inch and twist that as well.

5. Apply your iron and then some solder to each wire therefore “tinning” them!

6. Finally, heat each terminal until the solder softens and attach each wire to each plug terminal. Bend the strain relief back around your exterior insulator and make sure the two terminals are not touching each other before screwing the rear housing back on the plug.

Again you can use your multi-meter to check for continuity from both ends and for shorts between the tip and sleeve. This repair is a great way to practice soldering. You may never need to buy another new cable again!

Keep sending your questions, comments and suggestions to
workshop@performermag.com