I would suggest you contact JBL to see if they can give you an estimate on repairing the speakers, or perhaps replacing the drivers.
https://www.amazon.com/JBL-CONTROL-Compact-Monitor-Loudspeaker/dp/B000U29P5O
If you feel you are handy enough, the remove the Bass Driver and look inside. You can test the individual drivers with a 1.5v AA or AAA Battery. Connect wires to the battery, and touch those wires to the Driver Terminals. If you hear a
click, then in the most basic sense the driver is working.
Keep in mind this
'click' only occurs when the battery make and breaks contact, you will hear nothing with the battery connected. Though with the battery connected current will still flow, you want to avoid having the battery connected for any length of time. Again, make and break contact several times and you should hear the speaker
"thud" or
"click". That is a primitive test, but it gives you a basic sense of the drives ability to function.
Next, there many be a fuse inside, typically on the Crossover Board. Check that this fuse is still good.
Also, while open, check for any loose wires or broken connections.
Look at the Crossover components. Typically there is very little that can go wrong with a Coil of wire, but Capacitors can fail. If any of them are deformed or bulging, they probably need to be replaced, which can be done easy enough if we can determine the value of the Capacitor.
Here is an example of a typical crossover just so you have some idea of what they look like -
Speaker Crossover, 2 Way, 3500 Hz, Linkwitz-Riley, 4 or 8 Ohm, A-1303
The Yellow somewhat cylinder looking objects are the Capacitors. The Coil of wire is obviously a Coil. The Black Object with the Gray Bar through it is also a coil, an Iron Core Coil.
Capacitors can also be vertical or horizontal Cylinders like these -
https://www.amazon.com/Qianson-Ajustable-Frequency-Distributor-Crossover/dp/B01IZ7JF2I
https://www.amazon.com/2-WAY-Replacement-Speaker-Crossover-Watts/dp/B00AF021NY
Check those aspects out, and let us know what you find.
Steve/bluewizard