Troubleshooting and fault analysis requires a good theoretical knowledge and analytical thinking. It is not something which can be studied from books, but has to be acquired through constant troubleshooting and experimenting. However, there are guidelines that can be followed to the troubleshooting process. Nearly anyone who is familiar with basic electronic theory can learn troubleshooting techniques and fix many types of electronic failures. To troubleshoot, you simply follow logical, step-by-step procedures to arrive at a solution. Basically, troubleshooting depends on the circuit complexity, on symptoms, and on the personal experience. The most common troubleshooting techniques are listed below:
Many times a simple issue such as a blown fuse or a flat battery is the cause of a circuit malfunction. Initially, therefore, ensure that the power cord is plugged in and that the fuses are not blown. If the circuit is battery powered, make sure that the voltage level is acceptable. If a power supply rectifier is present, check the level of the voltage at the output and make sure that the circuit is powered with the correct polarity.
This inspection is part of the so-called sensory checks. Sensory checks rely on the human senses to detect a possible fault. The visual inspection of the PCB is the simplest troubleshooting technique (which is very effective in many of the cases). The soldered joints have to be inspected thoroughly. If any doubts exist about the quality of a certain joint, it has to be re-soldered. The PCB has to be inspected visually for any burnt components.
Sometimes, components that overheat leave a brown mark on the board. They can be used as ‘starting points’ in the troubleshooting process and the reasons why they overheat have to be determined. It is bad practice simply to replace such components, without trying to find out what actually caused the component to overheat. In many cases, the reason is a faulty (or out of range) component near the failed component. It also has to be replaced.
Using a sense of touch:
Overheated components can be detected by simply touching them. However, this check has to be performed with extreme caution. The circuit has to be turned off, and some time allowed for the large capacitors to discharge. Always touch the components with the right hand only. This is important because in the case of electric shock it is less likely that the current will pass through the heart. If possible, wear insulated shoes.
In addition, care should be taken not to burn the fingers. Using the sense of touch is a very useful troubleshooting technique in circuits, where everything seems to work properly for a while, and then the circuit fails, due to overheating of a certain component. Identifying such components helps to detect the possible cause of the fault. Special freezing sprays are available, which allow instant freezing of components. If the circuit begins to operate properly immediately after the heated component is sprayed, this is an indication that this component is causing the circuit failure.
Before replacing the component, further investigation is needed to determine what caused the overheating in the first place.
When certain components fail due to overheating it is possible in most cases to detect a smell of smoke. This is usually the case, if the technician happens to be there at the time the accident occurred. If not, it is usually possible to detect the failed component by visual inspection afterwards.
This troubleshooting method relies mostly on the operator's skills and experience. Certain symptoms are an obvious indication of a particular component failure. This statement is especially true for an experienced electronic technician. For example, some TV service technicians can unmistakably identify the failed component in a TV set (even before opening it), by just briefly examining the symptoms.
Component replacement is a good troubleshooting technique for an experienced electronics technician, as it saves a lot of time and money. Moreover, this technique guarantees the success of the repair, because if enough components are replaced, eventually the faulty one will be replaced too. However, it is recommended that the amateur technician initially applies some logical thinking to the troubleshooting process.
This troubleshooting technique is not the most common one, but it is the most desirable, as it requires intelligent and logical thinking from the troubleshooter. This method is based on the measuring of the signal at various test points along the circuit.
A test point in the circuit is the point, where the value of the voltage is known to the operator. This troubleshooting technique relies on finding a point, where the signal becomes incorrect. Thus, the operator knows that the problem exists in that portion of the circuit, between the point where the signal becomes incorrect, and the point where the signal appeared correct for the last time. In other words, the operator constantly narrows the searched portion of the circuit, until he finds what caused the fault.
There are two basic approaches in conducting the signal tracing.
In the first approach, the signal check starts from the input, checking consecutively the test points towards the output. The checks are carried out, until a point when an incorrect signal is found. The second approach is to start from the output and to work backwards towards the input in the same manner until a correct signal appears.
Following these simple steps will often fix a broken components on circuit board. However, if you are still having issues I can recommend Testing Electronics Components by Jestine Yong to help you learn more on electronics repair (TV, computer monitor, vcd player, etc). This guide will teach you test methods to recognize fault in electronics circuits.