Silicon Chip Online - Do-It-Yourself Servicing

Electronics is a black art to the uninitiated. They marvel at all those colourful little components and wonder how on earth we "experts" can navigate that secret world armed only with a schematic diagram – which to them is somewhat akin to a magician’s grimoire written in a long-dead language. That is why, upon seeing that you own a soldering iron and multimeter, your next-door neighbour may disappear briefly, only to return with his TV, DVD player, lawnmower or quite possibly, his wife’s pacemaker.

"I don’t suppose you’d mind having a look . . ."

You either decline and explain that it’s not really your field and that it should be seen to by an expert or you spend a couple of hours poking around inside, after which you say "look, it’s not really my field and it should be seen to by an expert".

In reality though, many fault-finding techniques are really just variations on common sense. You might be surprised at just how many repairs you can successfully complete.

Play it safe

Get a portable Residual Current Device circuit breaker and "don’t leave home without it". Never assume that you don’t need one or assume that it will magically protect you from every eventuality. It won’t.

Never dismantle any unit with the 240VAC mains still connected. It is too easy to inadvertently touch exposed circuitry with the metal lid or drop a screw inside.

Switchmode power supplies are potentially lethal. Some of the parts operate at 240V AC mains potential and that can include heatsinks. Never work on a switchmode supply with power applied unless you are an expert and know exactly what you are doing.

Similarly, never power up a dismantled unit unless you are absolutely certain of the voltage distribution inside. Some manufacturers physically isolate mains and low-voltage circuitry but it is common to find a single PC board with everything mounted on it, including the mains transformer. Tape exposed mains connections and never make assumptions.

Treat every power supply as if every component were live, as there are many supplies where this is the case. If you do not find a decent-sized mains transformer in the unit, be especially suspicious, as you will probably be dealing with a switchmode power supply. In the case of colour television sets, they frequently have a live chassis. This means that it is not safe to touch any part of the electronics, including anything that looks like an earth, while the set is operating.

If you feel uncertain as to the nature of a power supply, limit yourself to passive tests and measurements with the power off. Watch very carefully for high-voltage electrolytic capacitors. These are common in switchmode power supplies and 300V of DC can easily blow the tip off your favourite screwdriver!

Finally, don’t work alone but ask for children to be removed from your vicinity, as they can be a dangerous distraction.