If your JBL Flip 4 speaker refuses to turn on, see the JBL Flip 4 Won’t Turn On problem page for possible causes and solutions. If your JBL Flip 4 speaker will not charge or won’t hold a charge, see the JBL Flip 4 Will Not Charge Or Won’t Hold a Charge problem page for possible causes and solutions. Try: Connect the power source. Then long press together: JBL Connect + Volume up. I have not tried it, but some sources say it is for exiting firmware update mode. So, no high hopes, but it's worth a try. Either way, I would say not to throw it away. At least here, in Romania, you can buy second-hand parts for it, like logic board, or sell your unit for parts. Maybe also in your country.
Hi, I’ve found that going into the so-called “low frequency mode” fixes it completely - after also having made a firmware update (so my firmware is now as of 1-aug-2020). For those unaware, “low frequency mode” does not put in a low frequency booster, as it might sound, but instead disables the sound processor. The same sound processor that cuts out quiet sounds also cuts low frequencies at high amplitudes, to avoid distortion - therefore they call this disabling “low frequency mode” because there will be no more low frequency CUTTING. So, thank you JBL, but I like my sound just as it is; if it’s so loud that it distorts, I can take care to lower the volume or put in an equalizer as I desire. So: longpress bluetooth + volume minus - go into “low frequency mode” a k a unaltered sound; longpress them again to return to “processed mode” Restarting or shutting down reverts to the default “processed mode”.