1314 Chapter 34
34.5.4.1 Original Plans and As-Built Drawings
As-built drawings are critical for service technicians
and for a designer of any future system expansion. Keep
a set of original plans as reference for any changes that
were made. Include a final block diagram (one-line or
riser diagram) in the as-builts.
34.5.4.2 Equipment Lists and Equipment Owner’s
Manuals
Keep an accurate final equipment list. Both the install-
ing contractor and the end user should keep owners’
manuals since these may not be available if equipment
becomes obsolete.
34.5.4.3 Software Configurations and Backups
Backup the configuration files for DSP systems. Sound
systems may be used for a decade or more before being
replaced. For this reason, it’s a good idea to keep copies
of the software used to configure/program the DSP
since newer versions may not work on older hardware.
34.5.4.4 Approvals and Certifications
Keep rigging drawings and approvals and any other
safety agency approvals such as those from a local fire
marshall.
34.5.4.5 Additional Documentation
Keep a written record of all system settings such as
amplifier-level control settings and equalizer control
settings.
34.5.5 Troubleshooting a Sound System
Repairing a sound system may require the skills of a
trained technician. Troubleshooting, that is, finding the
problem, is something almost anyone can do if they
- Know the block diagram of their system.
- Understand what each component in the system is
supposed to do. - Know where to look for common trouble spots.
34.5.5.1 Know the Block Diagram
A sound system block diagram explains how the various
components in the system are connected to each other
and what happens to a signal as it flows through the sys-
tem. Because the block diagram shows the way the
sound system operates, it is extremely useful in the trou-
bleshooting process.
As obvious as it may sound, it’s not possible to tell
whether a component is working properly or not unless
its original function is well understood. Thus, it’s a
good idea to keep instruction manuals on all compo-
nents handy. Some repairs are as simple as repositioning
a control knob or throwing a switch that someone has
inadvertently changed.
Cables and connectors are by far the most common
sources of problems in audio systems. This is the best
reason to keep lots of spares, especially of cables that
are moved around a lot, such as microphone cables.
Other common trouble spots are fuses and circuit
breakers, as well as switches and controls that are in the
wrong positions, and problems with house ac power.34.5.5.2 Logical TroubleshootingThe process of troubleshooting involves logical thought
and methodical tracking down of a problem by
elimination.
Logical thought processes come into play when a
problem first occurs. If a single microphone goes
suddenly dead, logic says that the power amplifier prob-
ably isn’t at fault. If, on the other hand, an entire system
is suddenly quiet, the power amplifier might be at fault,
because it’s not likely that all the microphones have
failed at once.
A methodical elimination process, as shown in Figs.
34-79 and 34-80, can track down the source of most
problems very quickly. The idea is to find out what
component (microphone, cable, mixer, amplifier, loud-
speaker, etc.) is causing the problem and to replace or
repair it. During a live performance, of course,
replacing a faulty component is the most likely cure
since a repair might take up too much time.
The system mixer is a good place to begin the trou-
bleshooting process because it has the controls for the
entire system. A noise in the system, for example, can
be traced by looking at the VU meters or listening to a
PFL (pre-fade-listen) circuit with headphones. This
alone, may indicate that the noise problem is coming
from one microphone. Pull down the fader for that input
channel. If the noise goes away, check out the micro-
phone, or more likely, the microphone cable.
If the entire system suddenly goes dead, again, check
out the VU meters or listen to the PFL. If they are still
active, then it is most likely that the system is working
through the mixer (it’s still possible that the output
circuits of the mixer are at fault). Thus, some compo-