How to Check a Fuse

CHAPTER 10: Mending and Breaking Electronics 237

Just remember that taking things apart usually voids their warranty.

By following a few simple rules, you shouldn’t have any problems.

● Have a clear working area with lots of room. ● As you take out the screws, place them in the same pattern on your worktop as they were in the case they came out of. Sometimes the screws can be different sizes. If they are likely to be knocked or roll about on the surface, then push them into a piece of expanded polystyrene or something similar. ● After undoing the screws, when you come to take the case apart, watch out for any little plastic bits like switch buttons that might fall out. Try and keep them in place until you are ready to remove them. ● If something looks tricky, draw a sketch or take a photograph. (I tend to take a lot of photographs when repairing things, like with a hair dryer or straighteners, that have a large mechanical design component.) ● Try not to force things apart. Look to see where the clips are. ● If all else fails, try cutting the case apart with a handsaw (something your author has resorted to in the past), and then later glue the case back together.

How to Check a Fuse

The most convenient problem to fix in an appliance is the fuse. It’s convenient because it is easy to test and easy to fix. Fuses are basically just wires designed to burn out when the current flowing through them gets too high. This prevents further damage to more expensive components, or can stop a fire from starting.

Sometimes fuses are clear, so you can see that the wire inside them has broken and that they have “blown.” Fuses are rated in amps and will generally be labeled to show the maximum current in A or mA they can take. Fuses also come as “fast blow” and “slow blow.” As you would expect, this determines how fast the fuses react to over-current.

Some household electrical plugs contain a fuse holder, and you can also find fuses on PCBs. Figures 10-2a-c show the

238 Hacking Electronics

(a) (b)

(c)

inside of a UK fused plug and also a fuse holder on the PCB for the author’s multimeter.

You have used your multimeter in Continuity mode enough times now that you can probably guess how to test a fuse (Figure 10-3).

If a fuse has blown, there may be a good reason for this. Occasionally, however, they blow for other reasons, such as a momentary spike in the electric power lines or when turning on a heating element on a particularly cold day. So, generally, if there is no obvious sign of a problem with the device

Figure 10-2 Fuses