How to diagnose B&W speaker 'protect mode'

Thread Starter

Elliott Balsley

Joined Aug 31, 2016
21
Someone gave me a Bowers & Wilkins A7 wireless speaker, and I'm trying to figure out how to diagnose and fix it. It works great for about 20 minutes, then starts flashing red, which means it's in "protect mode" and needs to be sent into the manufacturer for repair. Unplugging the power for a few seconds is enough to reset it, then it works again. I'm guessing maybe something is overheating? Visually inspecting the capacitors inside, I don't see anything wrong. What's the next step to find the problem?
 

#12

Joined Nov 30, 2010
18,224
Are you good enough to make your own schematic by tracing out the board?
Without any sort of schematic there is nothing but guessing.
We don't have any idea what the speaker is measuring to conclude that it should protect itself.
 

RichardO

Joined May 4, 2013
2,270
You can try cooling different sections of the circuit to see if it will reset without cycling power. I suspect that it will not.

If that is the case then you will have to do it the hard way. Cool a section. Cycle power and see if it takes longer to fail. Repeat.

A spray circuit cooler will work but you will use a lot of it. An alternative is to judiciously apply isopropyl alcohol using a small brush. Use alcohol with as little water as possible to keep from shorting out sensitive circuits.
 

#12

Joined Nov 30, 2010
18,224
You can try cooling different sections of the circuit
Cooling is better than nothing, but we don't know if it has an MPU or just some basic power measurements.
Being a wireless speaker..does that mean is has its own power supply? Is it batteries or a wall plug?
 

RichardO

Joined May 4, 2013
2,270
Cooling is better than nothing, but we don't know if it has an MPU or just some basic power measurements.
Being a wireless speaker..does that mean is has its own power supply? Is it batteries or a wall plug?
Lacking a schematic I think it is time for some good pictures to help answer these (and future) questions.
 
"protect" for a typical amplifier means there is DC on the speaker terminals, but it can mean anything. The DC voltage should be no more than +-0.750 and usually very near zero.

If this is a class AB amplifier, then the current across the emitter resistor is increasing over time and eventually reaches the "protect" threshold.

Protect could mean many other things.
 

Thread Starter

Elliott Balsley

Joined Aug 31, 2016
21
These are the two main boards, front and back. There is another board for the WiFi.
This unit has AC power input. No batteries, no fan. It has WiFi and RJ-45 for AirPlay, and a combo input jack for 3.5mm analog and Mini Toslink.

It enters protect mode even when there's no audio playing. These are high-res photos if you download them.

IMG_2625.jpgIMG_2626.jpgIMG_2627.jpgIMG_2628.jpg
 

Sunnyjim

Joined May 15, 2020
1
Someone gave me a Bowers & Wilkins A7 wireless speaker, and I'm trying to figure out how to diagnose and fix it. It works great for about 20 minutes, then starts flashing red, which means it's in "protect mode" and needs to be sent into the manufacturer for repair. Unplugging the power for a few seconds is enough to reset it, then it works again. I'm guessing maybe something is overheating? Visually inspecting the capacitors inside, I don't see anything wrong. What's the next step to find the problem?
There is a fellow in France that made schematic sketches of the power supply I can send you a link if you are still keen.
 
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