How to test Subwoofer Amplifier with only a multimeter

[jinu_j]

Hi Folks

Need some advice on how to test a subwoofer amplifier if i have access to only a multimeter.

Problem
I have a Boston Acoustics active Subwoofer (soundware S). Its rated output is 200W. But the output i am getting is very low i can barely hear/feel it even if put the gain at max. I replaced all the capacitors in the Subwoofer amplifier but still no change.

Is there anyway to test this without getting an oscilloscope/Function generator to see if the fault is with amplifier, driver or the source??

Any advice would be appreciated
Thanks

[jinu_j]

Sorry just wanted to add that i tried the following test:
1. I started a Test Tone 80HZ on a YouTube video on my TV which feeds to an AV receiver
2. I measure the Subwoofer output channel on the AV receiver and that was showing around 80Hz freq and AC voltage of around 0.2V
3. I measure the output at the speakers terminals on the Subwoofer and i was getting around 86 to 90Hz Freq and AC voltage of around 0.3V to 0.4V
4. The gain button of the subwoofer works fine and the volume reduces to zero if i move it to zero and the volume increases it if i increase but the max AC voltage i can measure at the speaker/driver terminal is 0.3 to 0.4 Volts at max gain setting.

So guess this means amplification is only marginally working ?? The power supply board is fine and supplies +34V and -34v and also provides +21 and -21v for the preamp (i guess). There is no drop in voltage.

ince there is output assume there is no break in the circuit and signal is flowing thru the amplifier board, its just not getting amplified to the extent it should.

Any ideas on how to trouble shoot ??