Troubleshooting and Repair (SER001)

One of the purposes of this book is to give an electrician some basic knowledge about electronic components and circuits-knowledge that is necessary to make simple repairs and install electronic equipment coupled to electric installations, powered from electric installations, or even found in a car. It is not up to the rader or professional of any field other than electronics to make complex repairs in electronic equipment.

This task must be left to professionals. But, depending on the problem, repairing electronic equipment is not difficult if an electrician knows some basic procedures. There are two kinds of problems with electronic equipment the reader of this section can solve:

1. Simple problems with the equipment circuit.

2. Problems due to the installation or operation of the equipment.

This section presents a basic look at symptoms and causes of simple problems the reader, who may not yet be familiar with the operation of electronic circuits, can solve.

Because we can't see, hear, or smell electricity, knowing exactly what is wrong in a circuit only can be discovered with the aid of instruments or a procedure using symptoms as a basis for troubleshooting.

Of course, this article is introductory, and a reader wanting to go a step further will need more information. If you want to go into the profession, you will have to learn much more in a technical course as well as obtaining access to a variety of technical databases. It is also important and helpful to read technical periodicals because they provide useful procedures and ideas on new technologies.

 

The First Step

If a piece of electronic equipment doesn't work as expected what are the basic procedures to find the cause and how then to repair it? It is a false idea (coming from the tube age) that you should replace a given part when a certain symptom occurs.

This is not valid for very complex equipment and circuits Where hundreds or thousands of interdependent components exist. In complex circuits the same symptom can occur when any one of many components fails, and in some cases, many of them fail at the same time. You must know how the circuit works to form a hypothesis about what the cause of the trouble is.

For a reader who is now starting with electronics, it is too early to try real troubleshooting and repair work in complex equipment. We can, however, provide some basic procedures to allow determination if the cause of a problem is inside the equipment (and requiring professional help), in the installation itself, the result of improper use, or some other external problem.

The basic procedures are also useful to determine the cause of simple problems that need no professional help to be solved, such as burned-out fuses, unplugged connectors, and broken wires.

 

Safety Rules of Troubleshooting

These are the most important items when working with any piece of AC-powered equipment, and even equipment powered by other sources can use high voltages. It is very important to know the hazards associated with the equipment you are troubleshooting. Electricity can kill and the electrician working with dangerous AC voltages must know that.

Don´t turn on the equipment without thinking about it first. Start with some analytical thinking. Be sure that you know how to operate the equipment you are troubleshooting before powering it on.

Don’t touch parts if you don't know what they are for or how they work. You can cause more damage to the equipment; a simple problem can be turned in an expensive problem.

Look for visibly damaged parts such as burned-out resistors, interrupted cables, and bad connections. Many problems have simple solutions. The visual inspection is the starting point in any troubleshooting work.

Learn from mistakes; incorrect procedures when troubleshooting can turn a simple problem into an expensive one. Let a tool fall inside equipment being tested causing a short and you will have a real example of what that means.

Working with modular parts: modern electronic equipment often uses modular parts. If you can identify the cause of a problem in a module, it is easier to replace the complete module than trying to repair it by looking for burned-out components.

Don't always trust your instruments. If you are using a multimeter to measure voltages or a resistance in a circuit and the reading is confusing, don’t assume that is something wrong with the circuit. In many cases, the characteristic of the multimeter and the presence of other components near the one being tested can mask the results. Using the multimeter is an art and only with experience can you begin to trust all the measurement made by this kind of instrument.

However, the multimeter is probably the most useful of all the instruments the electronics professional can have. It is very important for someone wanting to become an electronics professional to be familiar with all the uses of this instrument. The next section discusses some more of its uses.

Plastic canisters, plastic ice cube trays, eggs trays, and pill bottles can be used for sorting and storing screws and other small parts when you disassemble equipment. Use a notebook to mark the position of any screw in equipment tested if you have difficulty memorizing it. A leftover screw when reassembling a device can cause a big headache.

Don't force any part of the enclosure in equipment when disassembling it. If you have to force it, it may be because you are not doing things correctly. The direction you are moving the part is not the correct way or there are more screws to be taken out.

ESD (Electrostatic Discharge)-Some components, including the CMOS transistors and the are very vulnerable to ESD. Don't touch their terminals when working with them.

If possible, use a schematic. Many pieces of equipment have manuals or schematics that provide important information for the reader when troubleshooting. if you intend to go further in this field, knowing how to read a schematic is essential to the repair of any equipment.

 

Schematics

Schematics for many commercial equipment can be found at internet. Type the model and code of the equipment in the Google search.

 

Quick Tips for Troubleshooting and Repair

A totally dead piece of equipment or one with many functions affected may have a detective power supply. Check whether the circuit is correctly powered. For example, see if there is voltage in the AC power line.

Erratic or intermittent problems are almost always due to bad connections, such as cold solder joints or connectors that need to be cleaned.

Gradually changing problems (problems that decrease or disappear completely when the equipment warms up) are often due to dried electrolytic capacitors.

The majority of problems in equipment with many mechanical parts, such as VCRs, CD players, or DVDs, are due to mechanical or optical failures.

 

 


Circuit Bench