Yamaha DTXpress/DTXplorer/DTXtreme

You need to do some swapping around to determine if it is the pad. 
Swap the cable with another to make sure it isn't the cable.  Try the
pad in another input (inputs 2, 6 and 7 are 3 zone on the DTXpress
II).  While a factory reset would sort out any things you may have
tweaked, try picking one of the preset kits, and the preset trigger
setups if you aren't using those.  Make sure the input is setup for
the TP65 (I think you have probably already checked that).

It does sound like a pad problem; either a bad connection or faulty
rim switch.  If you have a two zone pad, you could try that in the
same input and see if that works reliably to confirm that the module
is ok.  

Keith.