Repairing BT speaker that won’t power or charge

[DaveInPA]

I’ve got a JBL charge 4 which is a Bluetooth speaker with a rechargeable battery and powered by usb-c. Been working great for many years and I usually just leave it plugged in all the time. This morning when I turn it on it powers up and then a few seconds later powers down. So I can’t help myself and have to fix this thing instead of buying a new one.

The battery says it’s rated for 3.7v and it’s reading 3.2v. I kept it unplugged from usb port and removed battery and hooked up a DC supply with 3.7v and it works just fine. I wanted to update the firmware as some on the internet said that could be the issue. However the app that connects to it sees it’s not plugged into the usb power and won’t let me.

Then I remove the small board that has the usb-c power in and also happens to have a usb-a power out to charge other devices. I confirmed that plugged in I’m getting 5v on one of the pins. I’m also getting higher voltages on other pins but not sure what that tells me. On the main board I see a chip for usb charging port controller and another chip for lithium ion usb charging.

So here’s my question. The device doesn’t work when plugged in with or without the battery attached. Does that mean the usb-c terminal is bad or something else went bad in the power circuit? Or do these devices have some sort of reason to require a working battery to be connected in order for it to power up?

I’ve got 12v li-ion chargers but no idea how t9 charge a 3.7v battery. If I could that would probably be my next step…

[KhronX]

I kept it unplugged from usb port and removed battery and hooked up a DC supply with 3.7v and it works just fine.

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I’ve got 12v li-ion chargers but no idea how t9 charge a 3.7v battery. If I could that would probably be my next step…

Well, if you have a DC supply that can put out 3.7v (hopefully current-limited?), then you should be able to charge the battery itself.

Measure / confirm which terminal is which, on the battery, before continuing!

Hook up the supply to the battery (+ to +, - to -), set it to 4v, current limit it to 0.5-1A, and turn it on. The voltage will jump up a bit, from the 3.2v you initially measured, but should bump against the ceiling set by the current limit. Let it be for a while, keeping an eye on the voltage & current. Once it's up to at least 3.6-3.7v, turn off the "charger", reconnect the battery to the speaker's circuitry and see if it helped any.