Byroncunningham's adventure here illustrates one advantage of using a separate subwoofer amp that goes on a shelf like your other components: no scary surgery or huge shipping cost required if the amp has a problem.
Although JL Audio Subs are indeed GREAT subs, if you are inclined to purchase one, I would at the very least, buy the LONGEST warranty that you can find, as they CANNOT fix these subs!!! My F112 went out after 4 years, and I called Barry @ JL Audio and was told that they DO NOT fix these, but instead want to charge approx. $1200.00 for my F112 and I'm sure much more for the bigger ones because they can only replace the whole Amp section. I was in disbelief that they had no fixes for these subs. My advice would be to forget about buying a used one completely, and in my case, I would not even buy another JL Audio Sub, as in the end, you are going to spend way TOO much money when it dies. Look at other reliable companies, SVS, Paradigm, etc!!!
Just repaired one.
The manufacturer has apparently used very low quality capacitors from CapXon. They are also 85deg.C caps, lame.
Not sure if this is intentional by JLaudio, or if they just did not know how bad caps the Chinese manufacturer used.
Deadness is specifically due to a 100uF 35V cap at the standby power supply failing.
I replaced all CapXons with high quality caps, like 125deg.C ones, Panasonic FC, Rubycon ZL and some Sanyo ones too.
The Bipolar cap were still fine in the one I fixed, but I am thinking about replacing them at the same go.
Also getting the amp module out is a bit tricky.
You have to remove the driver (screws are under the surround of the woofer) and then carefully hammer out the sub module with a mallet and sturdy piece of wood as an extension. It is very heavy, do not let it fall.
I have lots of photos of how to do this, I cannot attach them here but maybe on DIYaudio.