Help a (cute) tongue-tied Bluetooth speaker recover its voice

[cigmas]

This cute little cube of a device is working except for its central function: the speaker won't make a sound.

* Bluetooth pairing succeeds
* the play/pause button functions to play/pause a video on a paired phone

 Yes, I did check that the video isn't muted 

I don't know how healthy the internal battery is, but it measured at 4.18V so I wouldn't expect that to be the problem right now.

The model number is BTS3115, but there's no mention of the brand.

Ideas on what to diagnose next?

External views:




Manual:



Teardown:

[kjr18]

First thing to check is speaker. Measure it with ohm range, if it's anything more than 4 Ohms, then your speaker needs replacing.
Second thing is amplifier ic. Try to see if you can see anything on those two caps C5 and C6, both are for input. If there is nothing, your main ic might be faulty.

[cigmas]

Without de-soldering anything, I measured 750 k at the speaker wires...

By "see" do you mean on an oscilloscope? I don't have one, but I measured C5 = C6 = 2uF.

[TheMG]

Without de-soldering anything, I measured 750 k at the speaker wires...

So you've got either a broken connection to the speaker, or the speaker itself has gone open (either at the tinsel lead connections or the voice coil itself).

[cigmas]

the speaker itself has gone open (either at the tinsel lead connections or the voice coil itself).

Right you are! I managed to get the speaker out. Really difficult to get a properly focused close-up pic, but one of the wires is dislodged:




I wonder if some solder would find its way to the wire in the cone. Could that work as a repair? It looks really tricky working through the speaker basket. The whole speaker is 1.75" or 45mm in diameter.

Also, is that probably a 4 ohm 3W speaker? I'm guessing what looks like "40" is 4

[TheMG]

Yes looks like a 4 ohm 3W speaker.

The actual connection from the tinsel lead to the ends of the voice coil wire are underneath the dust cap (in the front of the speaker), and they are usually covered with a blob of glue as well.

Repair prospects on such a small speaker are not very good, disassembling it to get to the connections is likely to end up destroying the speaker, but you've got nothing to lose as obviously the speaker is unusable in its present state.

The other issue is unless you were to replace the tinsel lead with a completely new piece, it will be shorter than the original, which means increased stress and accelerated failure (repair, if successful, unlikely to last very long). These connections are under a lot of strain due to the rapid movement of the speaker cone.

I would just look around for a suitable replacement speaker, they ought to be pretty common.

[cigmas]

So far, electronics stores I consulted don't carry speakers of this size/type. I see some on ebay but they cost more than anticipated, plus there's the long delivery time. I might still go that route if I don't find an alternative.

What exactly is the watt rating for speakers? If it is the maximum power tolerated, will a higher rated speaker be ok if the resistance and size match otherwise?

I went feeling around the tinsel wire's hole (seen in the pic above) with a multimeter probe and it makes contact (and reads 4 ohms) near the opening, but I don't see the wire. My first thought was whether I could just apply some solder and reattach the wire without dismantling the speaker, but it seems like it would be really tricky with a low probability of success.

[amyk]

Yes, it's a maximum power. Ones of higher rating but same impedance will work fine without damage.

[cigmas]

Yes, it's a maximum power. Ones of higher rating but same impedance will work fine without damage.

Good to know, thanks.

Any suggestions for the best chance of a repair?

[cigmas]

In the end I got replacement speakers from ebay (~$4 USD for a pair) and now it works.

I used a hairdryer to soften the glue holding the speaker into the plastic frame and it came out without too much difficulty. Luckily the replacement speaker matched in size perfectly. I later used some hot glue to secure it in place.



A postmortem found that the tinsel wire is joined to the voice coil wire with a blob of solder, and somehow one of those connections had come undone, while the other was still quite strong and took a lot of prying to break apart. At least I gained a few magnets and thin wire for the efforts.



The thin stranded wires connecting the speakers to the PCB are also very delicate. At the point where they are soldered to the board, a bit of flex quickly weakens them. I would not be surprised to have to take it apart and resolder those connections... but for now, the cube speaker has regained its voice! Thanks to everyone in this thread for the help!