Yamaha DTXpress/DTXplorer/DTXtreme

hi,
i have a dtxpress2, and have expanded my kit by buying a single zone 
cymbal pad, a dual zone cymbal and a tom pad. I used the dual zone 
to replace the single zone ride cymbal and then connected the ride 
and my new single into the 9/10 input. All of this works fine.

the tom pad is plugged into the pad in on the kick pad, but whatever 
id do, i can;t get it to work.
i've tried differnt cable, different tompads etc. i was convinced 
that either the dtx or the kick pad were damaged, and i worked out 
it's not the dtx by plugging a dual zone cymbal into the kick input 
(i got 2 sounds). This leaves me with the conclusion that something 
is wrong with the pad in on the kick pad. 

can anyone help me out on this?

cheers