Repair BOSE Speakers

BOSE CompanionⓇ2 Series III Computer Speakers

Recently, the sound volume from the speakers become unstable.

After turning the knob to a 9 o'clock position, the volume was stable for a while (checked with white noise) and started to go high or low. Usually went low when preset lower than 9 and when higher for higher preset.

Tried to open the speaker and fix it at first, by I couldn't find any screw from the housing, and it seems to be tightly assembled. I checked the website and the repairing quotation is not so favorable. So I decided to fix it myself with a backup plan to buy a secondhand set.

After checking cables and signal sources, I am sure that the cause is the knob for volume control. Here are the checking procedures:

1. Cable: change different 3.5mm cable 
2. Audio source: change from iPhone to a CD player and a Chromecast-ed monitor with the audio output port
3. The problem happens to both speakers at the same time
4. Carefully bend the knob and hold at the same indication makes the volume changes a lot.

I found a page in Japanese (http://akatsuki-tantei.net/article/474679151.html) about opening the case of the right speaker and re-solder the wire to the speaker unit. As I expected, the 8 snaps with glue prevent the user from opening it. So if I have to open it, I would definitely damage the housing somehow. Anyway, please refer to the above page for picture and have a idea about opening this speaker.

I used a flat driver to run into the gap and leverage the case along the sides. Overall, I broke 4~5 snap-fits. Unscrew the fixations, and the PCB with the knob is free to go after pull out the plastic cover from the front. 

The knob connects to a switch-potentiometer. A 10-kilo-ohm potentiometer with a switch with the connection between SW1 and SW2 will be closed if turned clockwise. I assume the switch is connected to the digital processor and activates the signal processing. As I can't find a supplier here, I decide to short the connection between SW1 and SW2.

I scavenged an old speaker and got a 10-kilo-ohm potentiometer. The original switch-potentiometer is larger. The footprint is also different from the scavenged one; I wire the pinout directly to the PCB and solder accordingly. If the 10-kilo-ohm potentiometer is not on hand, I guess any value between 500 to 20k should be acceptable.

Putting everything back in position and cleaning up the housing, trim off the deformed frame, the speaker is ready to work. A common miss is the wiring of the potentiometer. This may result in the opposite logic for volume control, fixed volume in maximum or minimum.

I checked the potentiometer manufacturer's page but can't find the exact product. They guarantee 10k times service life but in my case, far less than that. Anyway. Happy it's back.