This can be because the very thin insulating layers within the device have broken down completely due to high voltage static electricity, carelessly applied to the terminals. Sometimes this will result in a transistor (or a circuit board) not working when fitted within a system. Bad handling of FETs can lead to damage by electrostatic discharge. Sometimes external causes may damage or even destroy transistors. Always check the voltages at the transistor terminals after replacement to make sure there are no abnormal readings. In such circumstances it is wise to investigate the reasons for the failed transistor rather than just replacing it. This may eventually result in a transistor operating outside its normal parameters, for example running at a higher than permitted temperature. The reason for this is that other components such as resistors may change their values with age, especially if they are subject to heating effects caused by current flow. However older systems containing transistors do begin to give more problems. A slice of silicon 10 years old should be the same as a 1-year-old slice. There is no real reason that transistors should suffer from aging. Items that survive these tests can confidently be put into regular use. That is running it on a test bench for a number of hours to make sure no early failures occur. A large proportion of manufacturing faults can be detected by "soak testing" new equipment. If it operates correctly for this period then the chances are that it will continue to do so. If there is a fault in a new transistor, it will often show up in the first few hours of use. Manufacturing faults do (very occasionally) occur, usually in new equipment. Provided they are operated correctly there is no reason for them to fail at all but of course they do fail and this can be for a variety of reasons. Section 7.2 Meters for Transistor Testing.Īll semiconductor devices are extremely reliable.
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