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Appendix D: The Servo Amplifier Protection Circuitry
As noted in the “Guided Tour” section of this manual, the Servo Amplifier's front
panel Protection light indicates the activity of the relay speaker connection
circuitry. When the Protection light is lit, this circuitry is inactive, and all
connected speakers are muted (provided with 0 volts DC), thus protecting them
and preventing any audible “thump” from occurring.
The following conditions will cause the Protection light to go on:
• Initial power-up: For approximately five seconds after initial power-up, the
relay speaker connection circuitry is deactivated and the speaker output is
muted. If everything is operating normally, you will hear an audible click at the
conclusion of this brief period, as the circuitry is activated and the Servo
Amplifier begins delivering signal to connected speakers. It is normal for the
Protection light to fade gradually after the amplifier is powered off.
• Overheating: A temperature sensing device in the Servo Amplifier will cause
the relay speaker connection circuitry to be deactivated (and the Protection light
to go on) whenever the operating temperature of the unit rises above a safe
level. To guard against this problem, make sure the Servo Amplifier receives
adequate ventilation on all sides (see page 7 for more information); in extreme
environmental conditions, you may also want to consider the use of cooling fans.
• Severe overcurrent conditions: This occurs whenever the signal being input to
the Servo Amplifier rises to a level above 20% THD (Total Harmonic Distortion).
• Shorted speaker cables: This will occur if, due to faulty wiring, the hot and
ground signals being output by the Servo Amplifier short one another.
• Output impedance drops below 2 ohms: This can occur if the Servo Amplifier
is connected to inappropriate speaker systems (see the “Setting Up and Using
the Servo Amplifier” section in this manual for more information).
• DC voltage detected at speaker output: The most likely cause of this is an
internal failure.
In general, any time the Protection light goes on (other than during the
approximately five seconds following initial power-up), there is reason to be
concerned. If this occurs, turn the Servo Amplifier off immediately and carefully
check all wiring and external devices in order to locate and correct the condition
that caused the light to go on in the first place.
WARNING: If the Protection light fails to go out (and you fail to hear the
accompanying audible click) approximately five seconds after power-up,
turn the Servo Amplifier off immediately and check all external devices
and wiring for possible shorts or other defects.
PROTECTION
