QSC Audio MD-FP152/64r - Manual (Page 6)

6
SIG (Signal) Indicator LED
The green SIG (signal) indicator alerts the user to the presence of an input signal to the MD
loudspeaker.
Normal Indication
The green SIG indicator illuminates when the input signal exceeds -25 dB.
If No Indication
Check Gain settings and increase gain if necessary. Check input connections and audio source
for signal. If the red LIM LED illuminates, refer to the LIM indicator section, below.
Abnormal Indication
If the green SIG LED illuminates with no signal input, there may be system oscillations or some
other malfunction. Disconnect the input or fully reduce the gain. If the green SIG LED remains
on, the amp may need servicing.
LIM (Limiter) Indicator LED
The red LIM indicator alerts the user to several abnormal conditions within the MD loud-
speaker:
Continuous Bright Red Light
• Indicates protective mute mode.
• The speaker normally passes through muting for several seconds after applying power, after
which the light should go out, and sound should be heard.
• If the speaker enters Mute during operation, it has either overheated or developed a fault.
• Overheating should correct itself within 1-2 minutes, after which sound should resume. See
below for a full explanation of thermal protection.
• Short periods of muting indicate a component fault. In this case AC power should be removed
and the speaker serviced.
Momentary Bright Red Flashes
• During operation, bright flashing indicates clipping (overdrive distortion).
• This is normally due to excessive volume, and will likely be accompanied by audible distortion.
• If the speaker mutes repeatedly during peaks, there may be a component fault. AC power should
be removed and the speaker serviced.
Continuous Half-bright Light
• Indicates that the internal limiter is reducing gain, due to prolonged clipping and/or excessive
temperature.
• After several seconds of severe clipping, the limiter will reduce power to protect the speaker
and improve the sound. This results in a steady, half-bright red indication. Any further clipping
will still result in bright flashes on top of the steady half-bright indication. When the program
level is reduced, the limiter will clear after several seconds, and the red indicator will go out.
• If the power module overheats, the first response is to trigger limiting, to reduce volume and
limit further temperature rise. This results in a steady half-bright illumination that does not clear
even after reducing program level. It may take several minutes for temperature to drop and clear
the limiter. During this time, the exposed heat sink will feel uncomfortably hot to the touch. If
overheating continues, the amplifier will ultimately mute, resulting in a full-bright red indication.
When muting clears, the amplifier will resume operation, with thermal limiting still active until
it further cools off.
• Overheating is usually caused by excessive ambient temperature, since the internal temperature
rise of the Class-D power module is relatively low. Protect the speaker from excessive tempera-
tures, such as being placed over a heater vent, or allowing direct sunlight to impinge upon the
heat sink surface.
LIM (limiter)
indicator LED
SIG (signal)
indicator LED