GTH 400 (serv.man2) - JBL Car Audio User Guide / Operation Manual. Page 23

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Power light is on, but no sound is heard

• Defective head unit or signal processor; 

from some or all of the speakers

check each component for proper wiring
and operation.

• Defective GTH400; If there is audio 

signal present at the inputs of the
amplifier and there is no output, the
GTH400 may be defective.

Alternator whine through the audio system  • Ground loops; follow the wiring 
with the engine running

suggestions in the section called
“Solving Noise Problems.” Also, verify
that the chassis grounding point you
have chosen is true ground by checking
for continuity between the chassis
ground point and battery ground.

Bass output from speakers too low

• Speaker wired out of phase; check for

proper polarity on all speaker wiring 
(+ amp terminal to + speaker terminal
and – amp terminal to – speaker 
terminal).

Amplifier Power Light is on and

• Verify that the remote control is not set

sound is heard from the front and rear

in “BYPASS” mode by checking to see

channels but the Imaging is not improved

that the “ON” LED is lit.

with the image enhancer on

• Using the system configuration diagram,

confirm that the audio connections are
correct for signal path and polarity. Note
that right hand drive car installations
must have the Left and Right input and
output connections reversed as shown in
the wiring section on page 19.

• Perform the adjustments as directed in

the Imaging Enhancer Setup section.

Power light is blinking and

• Incorrectly connected or shorted speaker

no sound is heard

wires; check for shorts in wiring.

• Defective GTH400; if there is no short

on the speaker outputs, the GTH400
may be broken. Consult your JBL dealer.

GTH400-20107  06/03/98 15:50  Side 22