I assume that your 'power function switch' is set to auto? Have you tried it in the 'On' position, and if so does the speaker stay on all the time? Are you using the +12VDC Trigger input, and have you checked that voltage level from the amp is correct? Are you using the correct lead?
If you're relying on the input signal to keep the speaker on, is the level from the amplifier set high enough? (You may have to re-calibrate your amp)
If you look at the circuit diagrams posted earler, there are some notes about what logic levels to expect at the pins of the microcontroller (IC109), so...

I've just managed to repair my BXW-10 by replacing just one capacitor! C149 (22uF) was showing signs of leakage around its pins. There was a small amount of grey residue on the top of the PCB, but at first I didn't think it was that significant. I decided to change the output FETs as the most likely cause (and what a hassle that was - you need a right angle screwdriver) but the originals actually tested OK. C149 was then changed as the voltage rating of the fitted component was only 25V, which is incorrect according to the circuit diagram. I put in a Panasonic FR 50V cap and all was well.
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