Gain control not working

Hi guys, 

I have a 2.1 system in my lounge, probably 4 years old but not used that much. The gain control knob on the subwoofer has started playing up- it works on minimum and maximum, but when set anywhere inbetween the sub doesn't produce any sound. When transitioning from that minimum setting to anywhere in the middle, or from the middle to the max, the subwoofer thuds as it does when turned on/off.

Does anyone have any ideas on how I might be able to fix this?

Many thanks
You don't mention what sub you have, but I suspect there may be corrosion in the sub's volume pot. If you can access it, try spraying some electrical contact cleaner, while you twist the pot up and down. This may clean things up, and get your sub working again.

Also, if that doesn't help, see if the sub's volume control can be bypassed, and control its output through your preamp-processor (assuming you have one).

Good luck,
Thanks Dan, 

it's nothing fancy, just a punchy Philips system. I'll try the contact cleaner, I didn't suspect this as there is no crackling etc as you adjust it- it just completely cuts out, but will give it a go

many thanks