NUMBER OF JUNCTIONS
You may also find other markings on transistors that do not relate to the JAN marking system. These
markings are manufacturers' identifications and may not conform to a standardized system. If in doubt,
always replace a transistor with one having identical markings. To ensure that an identical replacement or
a correct substitute is used, consult an equipment or transistor manual for specifications on the transistor.
Transistors are very rugged and are expected to be relatively trouble free. Encapsulation and
conformal coating techniques now in use promise extremely long life expectancies. In theory, a transistor
should last indefinitely. However, if transistors are subjected to current overloads, the junctions will be
damaged or even destroyed. In addition, the application of excessively high operating voltages can
damage or destroy the junctions through arc-over or excessive reverse currents. One of the greatest
dangers to the transistor is heat, which will cause excessive current flow and eventual destruction of the
To determine if a transistor is good or bad, you can check it with an ohmmeter or a transistor tester.
In many cases, you can substitute a transistor known to be good for one that is questionable and thus
determine the condition of a suspected transistor. This method of testing is highly accurate and sometimes
the quickest, but it should be used only after you make certain that there are no circuit defects that might
damage the replacement transistor. If more than one defective transistor is present in the equipment where
the trouble has been localized, this testing method becomes cumbersome, as several transistors may have
to be replaced before the trouble is corrected. To determine which stages failed and which transistors are
not defective, all the removed transistors must be tested. This test can be made by using a standard Navy
ohmmeter, transistor tester, or by observing whether the equipment operates correctly as each of the
removed transistors is reinserted into the equipment. A word of caution-indiscriminate substitution of
transistors in critical circuits should be avoided.
When transistors are soldered into equipment, substitution is not practicable; it is generally desirable
to test these transistors in their circuits.
Q34. List three items of information normally included in the general description section of a
specification sheet for a transistor.
Q35. What does the number "2" (before the letter "N") indicate in the JAN marking scheme?
Q36. What is the greatest danger to a transistor?
Q37. What method for checking transistors is cumbersome when more than one transistor is bad in a
Transistors, although generally more rugged mechanically than electron tubes, are susceptible to
damage by electrical overloads, heat, humidity, and radiation. Damage of this nature often occurs during
transistor servicing by applying the incorrect polarity voltage to the collector circuit or excessive voltage
to the input circuit. Careless soldering techniques that overheat the transistor have also been known to
cause considerable damage. One of the most frequent causes of damage to a transistor is the electrostatic