TESTING ELECTRONIC EQUIPMENT
4-135. The two most widely used checks in testing electronic equipment are VISUAL and
SIGNAL TRACING. The importance of the visual check should not be underestimated
because defects can be found right away, simply by looking for them. A visual check does
not take long; in fact, you should be able to see the problem in about two minutes if it is
the kind of problem that is visible. Learn the visual check procedures found in Table 4-2
because you will find yourself using them quite often. This procedure is not only good for
power supplies but also for any type of electronic equipment you may be troubleshooting.
Table 4-2. Visual Check Procedures
BEFORE YOU PLUG IN THE EQUIPMENT, LOOK FOR:
SHORTS - Any terminal or connection that is close to the chassis or to any other
terminal should be examined for the possibility of a short. A short in any part of
the power supply can cause considerable damage. Look for and remove any stray
drops of solder, bits of wire, nuts, or screws. It sometimes helps to shake the
chassis and listen for any sounds of rattling. Remember to correct any problem
that may cause a short circuit. Even though it is not causing trouble now, fix it; it
may cause problems in the future.
DISCOLORED OR LEAKING TRANSFORMER
is a sure sign that
there is a
short somewhere. Locate the short. If the equipment has a fuse, find out why the
fuse did not blow. Sometimes a fuse that is too large may have been installed or
there may be a short across the fuse holder.
LOOSE, BROKEN, OR CORRODED CONNECTIONS - Any connection that is not in
good condition is a trouble spot. Even if it is not causing trouble now, fix it; it will
probably cause problems in the future.
DAMAGED RESISTORS OR CAPACITORS - A resistor that is discolored or charred
has been subjected to an overload. An electrolytic capacitor will show a whitish
deposit at the seal around the terminals. Check for a short whenever you notice a
damaged resistor or a damaged capacitor. If there is no short, the trouble may be
that the power supply has been overloaded in some way. Make a note to replace
the part after signal tracing. There is no sense in using a new part until the trouble
has been located.
AFTER YOU PLUG IN THE POWER SUPPLY, LOOK FOR:
SMOKING PARTS - If any part smokes or if you hear any boiling or sputtering
sounds, pull the plug immediately. There is a short circuit somewhere that you
have missed in your first inspection. Use an ohmmeter to check the part once
again. Start in the neighborhood of the smoking part.
SPARKING - Tap or shake the chassis. If you see or hear sparking, you have located a
loose connection or a short. Check and repair.
4-136. If you locate and repair any of the defects listed in Table 4-2, make a note of what
you find and what you did to correct the defect. It is quite probable you have found the
trouble. However, you must not take anything for granted. You must prove to yourself that
the equipment is operating properly and that no other troubles exist.
23 June 2005