Soldering




There should be a sponge on the stand of your soldering iron. Moisten it with some distilled water. Your soldering iron should be hot by now, if you turned it on while reading page 1! If not, turn it on now & give it a couple of minutes to warm up.

Once it has warmed up, look at the tip of your iron. Is it shiny with molten solder, or is it covered with dull crud? Wipe it on the damp sponge and touch a little fresh solder onto its tip until some melts onto it. If you melt too much, wipe it off on the sponge. Do not flick it onto the floor — the cleaners don't like it, and it may land on someone's leg!

When soldering components onto a ‘tracked’ board, put the leads through the correct holes and pull them until the component sits where you want it. (For resistors, capacitors, and inductors, this normally means the wires should be ‘straight’ as if pulled tight to hold the component against the board. For transistors, leave them above the board a little way as it can be a bad idea to pull their wires too much.) You may find it a good idea to bend the wires so they are ‘splayed out’ to help hold the component and stop it falling out when you turn over the board.

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Make sure the tip of the iron is ‘wet’ with solder and press it up against the lead and the track where they meet. Bring the solder into contact with this join and hold it there until some melts and wets the wire and track. Remove the strip of solder, then remove the iron.

Sometimes the solder will fail to wet the metal surfaces correctly and will have a dull or dirty appearance. They can also look more like a piece of rough coral instead of a smooth frozen droplet. Joints like this are sometimes mechanically firm (although usually not) but are poor or intermittent electrical contacts. They are, therefore, bad news. Bad joints are generally called “dry joints”. This is because they can be caused by not heating the solder enough. It then fails to reach the correct temperature. Alas, you can also get a bad joint if you over-heat the solder. Another cause is dirt or old solder on the leads or iron. Whatever the cause, use the iron to remove the “cold” solder, clean the iron and have another go.




Circuit Diagrams



Circuit diagrams are a language. You need to learn this language before the diagrams can be fully understood. This point isn't always grasped as the diagrams are often described as if they were 'pictures' of the circuits they represent. But a circuit diagram isn't really a picture, it's a pattern of standard symbols used to represent the real thing. It is a bit like ‘Chinese’ or perhaps like ancient Egyptian Hieroglyphics. Each symbol means something, and the ways in which things are linked also means something. However, the diagram isn’t a real ‘map’ as it doesn’t actually show you where things are on a real circuit board. It is a sort of logical description or ‘cartoon’ of reality. As a result, reading and understanding circuit diagrams can be quite difficult until you learn their language. So don't worry if the diagrams seem puzzling at first, they aren't always obvious!

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Note that when instruments or components are connected together in a diagram it is often assumed that the bottom line of the drawing is ‘earth’ (i.e. it connects points back through a terminal to mains earth). If you aren't sure about the meaning of a diagram - ask!







Content and pages maintained by: Jim Lesurf (jcgl@st-and.ac.uk)
using TechWriter and HTMLEdit on a RISCOS machine.
University of St. Andrews, St Andrews, Fife KY16 9SS, Scotland.