This is the part. I just removed it from the cab.
Thanks for posting that picture. troubleshooting and fixing this stuff for years, these are my assumptions.
You bang on the back of the cabinet to get sound. = You have a cold solder joint on that pc board. check with close up reading glasses under a bright light and stress the board, you will see something moving. Thats the culprit.
L-Pads are on a separate circuit from the woofers, your L-Pad could be on fire with molten lava pouring out of it and the woofers would still pass signal.
You Fender cab was probable made in China or elsewhere.
All the input connector jacks including components coming from that part of the neighborhood are CRAP.
I can't tell you how many made in Indonesia 1/4" jacks I've replace in over 25 years. You could have a visual check on the connections but it's always something you can't see readily. Like I said, yank the hole board fire up your soldergun and go hunting.
Piezo tweeter right?
Those has low output. I'd bypass the L-Pad all together and just hardwire that in the circuit.
Just my two cents. If you don't have the tools or soldering skills there always plan B.
