EEVblog 1605 - Chasing Fart Noises - JBL Charge 3 "Repair"

[EEVblog]

Dave is chasing fart noises in this JBL Charge 3 waterproof speaker.
A teardown, and powerup on the bench to find the mysterious fart noises.
Will it get repaired, or will the fault do a Harold Holt?

00:00 - JBL Charge 3 Waterproof Speaker Fault
02:17 - Teardown
07:13 - Drivers
08:16 - Passive Radiators
09:58 - The Case Moulding
10:46 - Main PCB
11:36 - Under the microscope
15:30 - What's this Power Rail doing?
18:07 - Power Rail Capture
20:16 - Are we chasing a red herring down a rabbit hole?
20:56 - Trying to capture the fault: Oscilloscope vs Microphone
22:22 - The Fault has done a Harold Holt

[JanWiesemann]

I’ve been having the same issue with my speaker as you where having. I didn’t think it was a electrical problem. Since I wasn’t in the mood for a repair I’ve already placed my speaker on the trash pile. Your video inspired me again and I look a look at it. One of the first things I’ve noticed while taking it apart was a speaker. The back magnet was loose and partially separated from the metal cage. I’ve removed the old glue and replace it with new epoxy. My speaker is now fully functioning again.

[Psi]

My speaker is not fully functioning again.

Did you mean to say "now" rather than "not"?

[HwAoRrDk]

I wonder if that anomaly with the output voltage on the boost converter is because the feedback is being actively driven by something else which is not initialised straight away at power-on (and also shut off before power-down). Inspecting the circuitry  connected to the FB pin would reveal what's going on. Because I can't imagine a passive resistor divider producing that result.

Maybe that is why there is a MOSFET switching power from the boost converter to the amp - they knew the flaw with the output voltage surge and didn't want the amp to see power until it has passed.

[Kleinstein]

The higher votlage could be a thing for a normal and high power mode. As far as I understood Dave the amplfier itself would support a higher voltage and it likely would need more than 5 V to get the full rated power.

A loose Magent, as shown by JanWiesemann, could be the issue, at least with a point to check, while the unit is apart.

[golden_labels]

In the video I can see the drivers are placed against the PCB, separated by foam. Perhaps at some frequency the speaker was hitting the PCB and taking things apart and putting them back together introduced some slight difference?

A less likely possibility: hitting resonant frequency of some component.

Or maybe the speakers just wanted to take a walk outside. Everybody needs fresh air!

[richnormand]

Four years ago I fixed a boom box for a friend that had a similar start sound and distortion at higher volumes on one side.

Both speakers had a similar start waveform on the scope.

One had the voice coil ripped from the speaker cone but still attached to the spider surround.
The fart sound is either the speaker hitting its edge travel limit (electronics or air leak)  or a detached voice coil hitting the limits (no load).
Scope voltage will be a bit different on each side due to loading but not much.

Have a close look at the suspect speaker.
I used superglue to tack the coil back to the cone, and when it was dry, epoxy glue for strength around the cone to coil.

Last feedback I got (three years later) is it still works (used in a noisy warehouse) so it has a rough life...

Best of luck with it.
Cheers.

 

[EEVblog]

A loose Magent, as shown by JanWiesemann, could be the issue, at least with a point to check, while the unit is apart.

Many people are confirming that the issue is also battery related, and/or battery contact related and they have been fixed that way. But it could indeed be mechanical as well.

In any case, mine works now and I have no intention of taking it apart again unless it fails.