So, I have this old JBL Flip 2, it didn't turn on, that was an easy fix, however, it stopped producing audio, I hooked up the speakers directly to my headphone jack
JBL CHARGE 3 Motherboard / Main Control Board OEM **ON SALE READ DESCRIPTION!** $9.99 - PicClick
GENUINE JBL CHARGE 2+ MOTHERBOARD MAIN BOARD 07-BTM153-0AG140 40-KB538U-MAE4G
JBL CHARGE 4 portable bluetooth speaker teardown - Qucox
JBL Charge 3 - Body and main board - YouTube
6000mAh GSP1029102R Battery Replacement Compatible with JBL Charge 3 (2015) and Select Charge 2+ Waterproof Bluetooth Speaker : Electronics