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p FJ> 'DJ . '"(,i (.' ,_,/_' t /'0\-, '.: .,..:.,.;;::~-..,--~ lt -often takes very little effort ·:.i/xpense to put new life into · defective stereo headphones. · . . By HOMER L. DAVIDSON Don't cry if your headphones become defective. Because there are only a few parts that can be defective, most headphone problems are very simple to troubleshoot. By making the repairs yourself you can save money too. Most service organisations would charge too much to make it worth your while to have headphones repaired and it would be cheaper to throw them away and buy a new pair. Unlike other audio devices which need expensive test equipment for effective servicing, headphone repairs require only a small soldering iron, a screwdriver or two, a pocket knife, and a multimeter when you need to make a continuity test. In fact, you don't even need a multimeter. To test continuity all you need is a battery and torch globe. headphones for use with stereo amplifiers have an impedance of about 8 ohms. Some headphones, such as those made by Sennheiser, have a typical impedance of about 400 ohms. Noisy Plugs Sometimes you'll hear noise that sounds similar to radio static whenever you touch or move the headphones' cable. This noise is often caused by tarnish on Many Different Kinds Stereo headphones are available in many different models and price ranges. You can purchase a budget pair of stereo headphones for just under ten dollars. On the other hand, better quality high-fidelity headphones can range up to several hundred dollars or more. Most stereo headphones have an impedance in the range of 8 to 50 ohms. Many of the headphones used with Walkman-type AM-FM radios and cassette players are around 32 ohms , while more conventional 14 SILICON CHIP The impedance of headphones used with personal portables and hifi systems is usually between II and 50 ohms. The most common prohlem is a wire breakage at the plug. the headphones' plug contacts - the tarnish actually functions as an insulator. If you can move the plug around in its jack and make the noise cut in and out, it's possible that the problem is tarnish. This can be removed from the plug's contacts with a paper towel moistened with contact-cleaning fluid (ie, Servisol). Defective Cord and Plug of the braid. (The common ground is usually found in budget-priced headphones). Obtain a replacement stereo phone plug from your favourite electronics store. Whether the plug is a fullsize 6.5mm type, or a miniature 3.5mm type, a stereo plug will have three individual metal rings. By contrast, a mono plug has only two metal rings for contacts. Suspect a broken cord, plug, or jack when one side or both earphones sound erratic or intermittent. If both are erratic, suspect a broken cord or poor connections at the plug at the end of the headphones' cable. Wiggle the cable close to the plug and near each earphone while listening to the music. You've discovered a break in the wire when the sound cuts in and out. More often than not, the wire(s) in the cable break right at the plug, or where it enters the earphone's case; rarely is there a break in the middle - between the plug and the earphone itself. Notice that there are three metal rings on the stereo plug. The ground (common) wire(s) connects to the largest (or outside) terminal. Slip the new plastic plug cover over the headphone cable. Solder the shield or common wire to the largest (or outside) terminal. (The common or ground connection goes to the longest metal ring area on a plug - the part called the sleeve). Connect and solder the remaining two wires to the plug's small terminals - these connections go to the tip and ring. Broken Junction Often, one of the leads in the cord breaks close to the plug. If the plug is a moulded-type, it may be cut off and replaced with a universal type. Always solder the connections; don't twist them. If there appears to be a break in the wire at the plug, cut off the broken cable at least two centimetres from the plug and strip back about 15mm of the outer insulation to reveal the wire leads from the earphones. Now separate the outside shield from each lead- this outside shield or braided wire is common to both earphones. In some cases, there might be three separate leads, with one lead serving as the common connection {ground) between the left and right earphones instead Sometimes, you may find a break in the cable where the wires connect at the cable junction - where the wires from the left and right earphones come together. To repair a break at the junction, remove the outside insulating material to get at each wire. Some flexible cables use tinsel wire wrapped around cloth threads and are difficult to solder because the wire often burns before the solder takes. To make sure you get the connection right the first time, apply a coating of rosin core soldering paste (not acid paste) to the tinsel wire(s) before you try to make a solder connection. Once you have tried and failed, it's usually too late to use soldering paste. Wrap a layer of plastic tape over each wire, and then one complete layer of tape over the spliced area. Defective Earphones You can check the headphone's wires for a break between the plug and the individual earphones by using two sewing needles and a multimeter or DMM (Fig.1). The needles are used to provide a connection to the wires without having to cut away the insulation. Simply push a needle through the insulation and into a wire. If you push a needle into the wire just where it enters the earphone, the wire can be checked for continuity from the plug to the needle by connecting your multimeter (switched to a low "ohms" range) between the needle and its matching contact on the plug. FEBRUARY1988 15 LEFT RIGHT set of headphones, you are no further behind. For low-cost headphones, pry off the plastic lid with a pocket knife to get at the earphone's speaker coil and connecting wires. The foam ear pad and plastic lid may be glued together after repairs are made. Fig.1: the earphone coils and their wires can be checked with the low range of a multimeter or DMM. Needles jabbed through the insulation provide direct connections to the wires for the test leads. Suspect a defective earphone if the continuity of each wire is normal to each needle. If only one earphone is defective, its resistance may be compared to that of the normal earphone. Sometimes, the earphone may be damaged - actually burned open - by excessive volume. This is possible because an earphone is essentially a miniature dynamic speaker, consisting of a magnet, a diaphragm, and a voice coil attached to the diaphragm. Excessive volume overheats and burns out the voice coil. Taking headphones apart to get at the driver inside generally involves a little butchery because they are usually glued together. However, any splits or cracks in the housings which may result when they are pulled apart can generally be made good by a little glue. And remember, if you don't manage to repair a defective GJ DMM An adaptor plug/jack will convert a miniature or subminiature plug for use with standard 6.5mm phone jacks. Check the continuity of an earphone's speaker-coil by using your multimeter's low ohms range. On most headphones, you should get a resistance reading somewhere between 8 and 50 ohms. Try to locate the wires from the cable that are soldered to the earphone's coil. Inspect the soldered connections. Sometimes, the coil's ultra-fine wire breaks off right at the connection. A mushy sound out of one earphone may indicate a defective integrated circuit or power amplifier, or a defective cone in the earphone's speaker. A defective earphone may be located by reversing the earphone leads at the plug. If the same earphone is distorted, suspect a defective cone. Check the amplifier circuit if the suspected earphone is normal when the wires are reversed. Trouble At The Socket While a headphones' stereo plug is often a cause for erratic or intermittent operation, the jack socket can also be troublesome. If you get erratic, intermittent or noisy operation and the plug checks out OK, wiggle the plug at the radio or cassette player's headphone socket and note if the problem persists. Sometimes you will hear sound if you push sideways on the plug, indicating a worn socket. If the problem appears to be in the socket, check it carefully no matter how good it looks. Often, the terminals of a headphone socket become fatigued with the repeated insertion of the plug and the only repair is simply to replace it. ic Fig.2: both the continuity of the cable and the individual earphones may be checked with the ohmmeter. The DMM resistance measurement is approximately equal to the earphone impedance. A very high or infinity reading means that the channel is open circuit. 16 SILICON CHIP Adapted from an original article which appeared in Hands-On Electronics. Copyright (c) Gernsback Publications, USA.