GTO-1001EZ - JBL Car Audio Service Manual (repair manual). Page 6

If your amplifier isn’t performing the way you think it should, check to see if the problem is covered in this section 
before calling your dealer or contacting JBL customer service.

No sound (the amplifier’s 
Power/ Protection LED is off):

•  Check that the amplifier’s +12V and GND connections have been properly 

made.

•  Check if the fuse on the +12V wire located near the battery is blown; if so, 

replace it with an identical fuse.

•  Check all amplifier fuses; if any are blown, replace them with identical fuses.

•  If you are using the amplifier’s REM connection for turn-on, check that the 

wire is properly connected to the audio system’s remote turn-on wire or to the 
vehicle’s ACC power terminal.

•  If you are using the amplifier’s Auto Turn-On circuit for turn-on, check that the 

amplifier’s Auto Turn-On switch (on the amplifier’s bottom panel) is set in the 
“On” position.

No sound (the amplifier’s 
Power/ Protection LED is 
orange):

•  Check that all amplifier input and speaker connections have been properly 

made.

•  Check that the amplifier’s Gain control is not turned all the way down.

•  Check that the vehicle audio system’s source unit’s volume control is not 

turned all the way down.

•  If you have connected an optional Remote Bass Control (sold separately) 

to the amplifier, check that it is not turned all the way down (fully 
counterclockwise).

No sound (the amplifier’s 
Power/ Protection LED is red):

•  Confirm that the vehicle’s electrical system is supplying between 9V and 16V 

DC to the amplifier. If the supply voltage is outside of this range, correct the 
condition before attempting to use the amplifier.

•  If the amplifier has overheated, wait until it has cooled down before attempting 

to use it again.

•  Disconnect all speakers from the amplifier and attempt to turn it on again: 

–  If the amplifier turns on (the Power/Protect LED is orange), there is a short 

circuit in one or more of the speaker wires. Correct all short circuits before 
reconnecting the speakers to the amplifier.

–  If the amplifier does not turn on (the Power/Protect LED is still red), contact 

your authorized JBL dealer for assistance.

•  If the optional Sub Channel Level control is connected to the amplifier, check 

that it is not turned all the way down (fully counterclockwise).

Sound is too quiet, even with the 
vehicle audio system’s head unit 
volume turned all the way up:

•  Check the amplifier’s Input Level switch. If it is set to “Hi1,” turn the amplifier’s 

Gain controls all the way down and re-set the Input Level switch to “Low.” 
Then perform the Set the Gain procedure, on page 7, again.

Sound in the subwoofer is 
distorted:

•  If the Input Level switch is set in the “Low” position, change the setting to “Hi1” 

and perform the Set the Gain procedure, on page 7, again for those channels.

•  While listening to bass-heavy music, turn the Bass Boost control all the way 

down, and then gradually increase it until the distortion begins to return. 
Reduce the Bass Boost control setting slightly to eliminate the distortion and 
leave it set there.

•  Check that the distortion is not originating from the vehicle audio system’s 

source unit.

The amplifier’s Gain LEDs 
constantly illuminate red while 
the amplifier is operating:

•  Set the amplifier’s Gain LEDs switch in the “Off” position.

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