Harman JBL VL18-SUB, User Manual

Page: 21 / 36

21
TROUBLESHOOTING
Symptom Likely Cause What to Do
No sound. The amplifier is not plugged into
the power outlet. Review if there is a damaged cable or if the
amplifiers are disconnected to the power outlet.
The power supply is not on. Turn on the power and check if the power LED is lit.
No sound, the amplifier is
connected to electrical
power but does not turn
on. The power cord of the amplifier is
faulty or improperly connected. Check the power cord at both ends. Replace with a good
power cord.
No sound, power on. Signal source (Mixer, processor, ...)
is not sending signal. Check if the signal LED of the amplifier is on.
The mixer or other source is
overloaded.
Check the Owner's Manual of your mixer and adjust the
controls as required. Once this is done, review the
instructions in the quick start guide
of this manual.
The sound is distorted
and too loud, the clip
LED is lit most of the
time. Excess of input signal,
attempting to exceed the
loudspeakers capacities.
Reduce the source output level.
Decrease the volume control of the amplifier.
Use additional VL18-SUB speakers.
Sound is distorted even
at moderate volume, the
clip LED is not lit. The mixer or other source is
overloaded. Check the Owner’s Manual of your mixer and adjust
the controls as required.

Input Sensitivity;
 Channel faders:

Main Faders;
Noises or whistles are
heard at the sound
output. Device or cable as source of
noise. Disconnect the devices that are connected to your mixer
one at a time.
If the noise goes away, the problem is with the source
or the connecting cable.
Noise and humming that
increase or decrease when
the level controls of the
mixer are moved. Inappropriate AC ground or faulty
equipment
connected to the output of the
mixer.
Disconnect or mute the channels one at a time, isolating
the problem. Please, refer to the user's guide of the
faulty equipment to solve the problem or help.
A faulty cable between the power
supply
of the equipment and mixing
equipment.
Replace defective cable with a good quality one.
Noise or buzzing
Inappropriate AC grounding,
ground loops. 
“Raise the GND” of the audio signal using an XLR /
F to XLR / M adapter at one end.
Re-route audio cables away from power and light cables.
The size of the unbalanced cable
is too long. 
Use the balanced output, (if available) on your
mixer or source of your VL system.
Poor regulation of earnings. Reduce the level of the INPUT controls and increase the
output level of your source device.