Is there a way to use the wireless subwoofer without the soundbar of the jbl sb400

Hello Donald Mikalajunas,

The Blue-Tooth is actually an incredibly similar
(small board)...

After going thru the owners manual...
I only found "quick start" instructions... (below).

~~

My best advice is to contact JBL... and hit their
TECHNICAL SERVICE... for the CIRCUIT BOARD...

HARMAN International Industries, Incorporated
8500 Balboa Boulevard,
Northridge, CA 91329 USA

>> 1-818-893-8411

Harman International Industries contact to us

Tell them you are an "ESD" qualified technician...

(easily done: NEVER handle semiconductors without
your ANTI-STATIC WRIST STRAP

>> ($6 ITEM: BELOW)).

JBL CINEMA SB400 Quick Start Manual Bluetooth

Carnac the Magnificent

is it the remote not working or the receiver not receiving
take your remote and point the lens at the camera of your phone
turn the camera on and when you press the remote button ( any button ) you will see a white dot on the phone screen if it is working

I have no experience of wireless speakers but I think you should contact the seller, if the unit is still under warranty or perhaps the support section of the manufacturer's website.
Certainly do read the instrucion manual.

I am guessing but either the wireless signal is being lost (depends on the function of the blue light) or the subwoofer is malfunctioning after a few minutes and the built-in thermal or overload protection is switching it off. The thump sound could be it trying to switch on again and finding the fault is still present.

Just my thoughts...

Does the power light come on? If not, check the power cord and power outlet on the wall. Maybe plug in a table lamp to the wall power outlet to make sure the outlet is working. If the power light is on, check the Mute button on your JBL remote control. Also check the Mute button on your TV if sound and picture go through the TV first.
We had a Harman Kardon soundbar (model SB30) made by the same company as your JBL. It worked great for a few months. Then there were a couple of funny high-pitched sounds that stopped when we turned the soundbar off and back on. Then a day or two later we truned on the soundbar and it was completely dead - no sound at all. Harmon/JBL replaced the soundbar under warranty with a refurbished one which lasted about two weeks and dies the same as the first one. Finally, they replaced the second one with a higher model (the SB35) which is still working, although it occasionally makes a rapid clicking noise for a moment here & there.

try connecting tv optical output to sb350 optical input

PAIRING THE JBL SB400 FOR WIRELESS OPERATION
After turning the soundbar and subwoofer on for the first time, you will need to "pair" the subwoofer and soundbar so they both operate at the same wireless frequency. To pair the units, press the Wireless Pairing switches on both units within 30 seconds of each other. The units will communicate with each other and operate at the same frequency.

I presume you need link the Wireless Subwoofer to tour Soundbar.
Here are instructions:
How To Link The Wireless Subwoofer To Your Soundbar HW Models Samsung

You need to press the bluetooth button on the bar. It's on the right, hold it until it flashes.

With some TV's you have to go into the menu, and enable an external sound device. If that doesn't work you can try to hook the tivo to the other HDMI inputs to make sure they work. If yes then, it's not your TV it's the soundbar. Hope this helps! Good luck!