2-12
PRECAUTIONS.—Transistors, although generally more rugged mechanically than electron tubes,
are susceptible to damage by excessive heat and electrical overload. The following precautions should be
taken in servicing transistorized equipment:
1. Test equipment and soldering irons must be checked to make certain that there is no leakage
current from the power source. If leakage current is detected, isolation transformers must be used.
2. Ohmmeter ranges that require a current of more than 1 milliampere in the test circuit are not to be
used for testing transistors.
3. Battery eliminators should not be used to furnish power for transistor equipment because they
have poor voltage regulation and, possibly, high ripple voltage.
4. The heat applied to a transistor, when soldered connections are required, should be kept to a
minimum by using a low-wattage soldering iron and heat shunts (such as long-nose pliers) on the
transistor leads.
5. All circuits should be checked for defects before a transistor is replaced.
6. The power should be removed from the equipment before replacing a transistor or other circuit
part.
7. When working on equipment with closely spaced parts, you will find that conventional test
probes are often the cause of accidental short circuits between adjacent terminals. Momentary
short circuits, which rarely cause damage to an electron tube, may ruin a transistor. To avoid
accidental shorts, a test probe can be covered with insulation for all but a very short length of the
tip.
Electrostatic Discharge Sensitive (ESDS) Care
Devices that are sensitive to electrostatic discharge (ESD) require special handling. You can readily
identify ESD-sensitive (ESDS) devices by the symbols shown in figure 2-5. Static electricity is created
whenever two substances (solid or fluid) are rubbed together or separated. The rubbing or separating of
substances causes the transfer of electrons from one substance to the other; one substance then becomes
positively charged, and the other becomes negatively charged. When either of these charged substances
comes in contact with a grounded conductor, an electrical current flows until that substance is at the same
electrical potential as ground.
