Yamaha DTXpress/DTXplorer/DTXtreme

Hi All,

I live in the UK and have had a DTXpress III for about 18 months - 
just home use for fun. Never had a problem until now and it's a weird 
one:

My hihat registers closed or open - foot on the pedal and hit pad = 
closed sound; hit pad with no foot on pedal and open cymbal sound. But 
when I try to use the hihat pedal on its own, I get no sound at all. 
Well, that's not entirely true: if I depress the pedal lightly, I get 
the faintest of sounds, but then nothing more on successive beats.

I tried a factory reset, but no change. The rest of the pads are 
working fine. Help! Any ideas?

Thanks for any advice.

Malc