Originally Posted by Jeff D
Checking to see if anyone ever found a cause for their problem. I've got a similar issue with my left speaker. With low volume the power to the sub cuts in/out (LED doesn't stay on) and when it comes on there's popping. Cranking the volume brings everything online for a while.
I've been on the fence if it's power supply, source, or cabling.
I think I'm going to tear it apart soon and inspect the power supply components, the caps would be my first guess, but power supplies are outside of my EE experience. Time to grab the tools and do some investigating.
I finally got around to checking out the sub's circuits. I started easy and swapped the input boards between the FR and FL speakers, the FL continued to show the problem so I moved onto the sub's power circuit.
This is the input board, nothing too crazy here.
I checked with BA to see if there's a schematic or any know components to fail which I wasn't surprise to find everyone at BA has no idea about these speakers. I was still thinking the problem was a capacitor, luckily there are only a few on the board. I focused two large 63V 4700uF caps (labeled C4 and C5) and the 3 25V 100uF caps (labeled C3, C7 and C8).
Here is the power board with the large caps and wires to the sub speaker removed. The two thick red wires in the upper left are 50V power input and the yellow wire going to the right side is a 25V power input. The red/black pair is for the LED on the front of the speaker. The ribbon connector on the right goes to the input board. You can see the three 100uF caps in the middle and middle right of the board.
I started with the large caps which were a bear to get off the board (time to consider a in-circuit cap tester!) I constructed a simple RC circuit to test the charge/discharge characteristics. I only had my 5/15V power supply so these charged pretty quick, but the discharge curve looked good.
Checking the three smaller caps I found the following charge/discharge curves for the caps:
These two have similar charge and discharge curves and they look good.
This one reached max voltage nearly instantly, obviously the last isn't right.
Sadly I didn't keep track of which capacitor this was, but my guess is it's the C3 capacitor. I replaced it with one I had laying around which has a charge/discharge matches the other two, must be good!
Hooking everything back up and the speaker works like expected!!! Now I just need to figure out if this random cap I used is good enough. I'm half tempted to replace all those caps but I need to find a better way to get these parts off the board!
Hope it helps someone else keep these speaker working. I know my wife isn't too happy we can't "upgrade" to tiny speakers!