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Soldering On

Soldering the professional way!


Almost every musician has to solder something at onetime or another - even if only to replace a damaged jack or XLR connector. You'll also need to know how to solder properly for when IN TUNE begins its series of easily-made accessories (appearing in the very near future). We asked ace wireman Geoff Lowther of Musicable to explain the correct technique.

Soldering - What Is It?



Soldering is a type of welding which is used to join wires and components to printed circuit boards (PCBs), connectors and so on. It is the basic skill you'll need in order to participate in the practical side of electronics, and it's a skill which, like playing a musical instrument is learned through practice. A good tutor also helps - so read on.

Choose Your Weapon



In order to participate in this stimulating physical activity, you'll need a few basic tools - the most obvious one being a soldering iron. When choosing an iron, it s advisable to consider the application you intend it for. For example, small PCB work will only require a small iron of say, 15-18 watts, whereas soldering of large brass areas, like heavy-duty jack plugs, will require power of 25 watts or more. Size should also be a consideration. A small iron is easier for working on PCBs and the smaller types of connector, such as DIN plugs. Whichever iron you buy, beg, steal or borrow (dodgy, that last one!), make sure the bit - that's the replaceable tip, the business end - is readily available. I assure you, there's nothing more frustrating than spending £12 on a temperature controlled 'Hokey-Cokey 2000', only to find that it's only good as long as the bit lasts! Stick to the 'Phirrips' version! Some of the better-known manufacturers and suppliers, such as Antex, S.R Brewster, RS. Components and Weller, should be a safe bet.

Other tools you will require are side cutters and a soldering iron stand. Bodgers take note: milk bottles and similar ad-hoc soldering iron stands tend to fall over with alarming regularity. When this happens, Sod's Law says that the iron will do a double somersault, burn the palm of your hand, the back of your hand, its own mains flex and the deep-pile carpet! You will also need some solder, naturlich, Ja? This should be the multicore variety with integral flux.

Electronics Hobbyists Do It In The Spare Room



Now to the nitty gritty, down to brass tacks, what you've all been waiting for, etc. Put your iron in its stand plug it in and set the controls for the heart of the sun! Get ready with some solder. When the iron is hot melt the solder so that it forms a coating over the tip of the bit. This process is known as 'tinning', and it's a good idea to keep the bit in this condition. You'll find that as you melt solder the flux burns off and leaves a mucky residue which will corrode the bit. In order to combat this state of affairs, it's best to wipe the bit on a dampened sponge to keep it clean. Most soldering iron stands have provision for one of these, and the sponge material should be available from any good radio store.

If the bit does become corroded, switch the iron off and let it cool down. When it's cool, clean the bit by rubbing with reasonably fine emery or carbundum paper, or use a fine file. Contour the bit so that the flat is at a convenient angle, turn the iron back on and repeat the tinning process. Keeping the bit clean like this will ensure good, fast soldering joints.

The idea of the game is to make a mechanical connection and then an electrical bond using solder, without damaging the article you're soldering through overheating. Let's use the example of a resistor and a PCB. Make sure the PCB and the legs of the resistor are clean; use a PCB cleaner such as Electrolube or RS. Components solvent cleaner. Now bend the legs of the resistor in order to fix it to the relevant parts of the PCB. Push the legs of the resistor through the holes in the PCB until it sits neatly on the board. Bend the legs protruding through the PCB away from the centre and flat to the board (see Diagram A). Cut the resistor legs so that the resistor grips the PCB without protruding beyond the track around the holes.

DIAGRAM A


Now comes the skilful part! In order to get the solder to flow over your mechanical joint, you need to heat the joint with a soldering iron whilst simultaneously applying solder. If you heat the joint without applying the solder at the same time, you'll lose out in two ways. One: the component may become overheated. Two: the joint will take much longer to heat up because of the lack of solder to aid heat transfer. So make sure the bit is tinned, apply the flat part and the solder to the joint for 2-3 seconds until the solder flows evenly, then remove the bit and solder gently, so as not to disturb the joint until it is cool (see Diagram B).

DIAGRAM B


Your joint should look even, and fairly smooth and shiny. If it is 'blobbed' rather than smooth, and rather matt in appearance, congratulations - you've made your first dry joint (see Diagram C). Dry joints are to be avoided, since they are a constant source of equipment breakdown. You can test for dry joints by gently wiggling the component on the PCB. If it moves, the joint is dry.

DIAGRAM C


If you are experiencing difficulty in getting the solder to flow smoothly on the joint and are applying the iron for a long time (four or more seconds), try removing the component and cleaning both it and the PCB thoroughly. If this doesn't solve the problem, check that you are applying the tip and solder correctly (Diagram B again). Failing this, your iron probably isn't hot enough. Check it out (though NOT by touching the bit with your finger!), and use another if necessary.

Wired!



When soldering wires and cables to connectors such as jack plugs and XLRs, the same basic rules apply. One difference is the mechanical connection. You'll find that most jack plugs and virtually all XLR-type connectors have some form of cable strain relief, and therefore all you have to worry about is making a good, clean joint on each connection.

In order to make a good connection it is imperative that, when applying the bit to the joint, the connector is held firmly in place. To this end a vice is a good idea - also, an old FX pedal with jack sockets is ideal for holding jack plugs for soldering! When you have the connector firmly held in the appropriate position and you've stripped the cable end, it's best to tin both halves of the connection. Apply bit and solder simultaneously to the connector contact or prepared wire for two to three seconds, taking care not to overheat the cable. Once this task is complete it's a piece of cake to make the joint. Hold the wire to the contact of the connector at the correct angle (small pliers or tweezers are ideal for this), apply the bit to the joint, and - voila! The solder melts. At this point take care not to move the joint as this is another way to make a dry joint (yes, there are many, and no doubt you'll discover them all given enough time!)

Watch Out For Old Smokey



Finally, a warning! Apart from the obvious pitfalls of burning the soldering iron mains flex, leaving the iron on and burning down the house, burning yourself, wiring the mains plug to your iron incorrectly and blowing the company fuse, there is a far more insidious health hazard. Solder fumes and definitely bad news, as the flux materials they contain are known to cause eye irritation, headaches, and no doubt all kinds of other nasty thingies. Solder is a lead alloy, too. So work in a well ventilated area, preferably with an extractor fan (that is, one of those blades driven by an electric motor, not your favourite heckler down the'Frog and Vomit' who always takes the rise!).

Well, that's it - everything you wanted to know, but were afraid to ask. Now rush down to your local radio store, pick up all the necessaries, and go for it. Good luck!



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C-Tape LP2 'Latin Percussion'

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On The Record


In Tune - Copyright: Moving Music Ltd.

 

In Tune - Jul/Aug 1985

Donated by: Gordon Reid

Feature by Geoff Lowther

Previous article in this issue:

> C-Tape LP2 'Latin Percussion...

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> On The Record


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