I'm in a somewhat similar pickle as the original poster. I've already tried some solutions and am hitting nothing but dead ends, so I figured I'd do a post before taking the next steps. Alas, my tale of woe is a bit on the long side.
I've got the Band Hero kit for Wii. For a couple months I was in good shape, but then one day my red pad started acting up such that it would respond if I hit it in one area, but not in another. I found my way to this site and bought one of the solderless replacement kids, swapped it out myself, and was ecstatic.
...that is, for a couple weeks. I then started to have the "double hits" symptom just like the original poster: Hitting either the yellow cymbal or blue drum would often cause the red to fire as well. I opened up the kit and wondered if maybe the sensor or its connecting wires were somehow loose, so I tried taping the sensor down to the back of the pad, though wasn't sure if that was a good idea. Needless to say, in the process of opening it up and fiddling with it repeatedly as I tried/tested these approaches, the black wire's connection to the sensor managed to snap off completely, so I gave up and placed the order for more sensors. This time I decided to just buy TWO since they're cheaper in bulk and that way if I managed to break another I'd not have to wait 5 days to try yet another test!
Once again, the swap-out seemed a success and I was in business for a couple weeks. And now today, we're back in the double hit zone. Having become adept at opening things up and now verrrry cautious about the possibility of snapping one of those wires loose from where they connect to the sensor, I verrrry carefully opened it up. I was surprised to find that the sensor was still 100% intact where I left it, and none of the wires visibly coming loose (that I could see). Thinking again of my prior idea of taping the wires down, I verrrry carefully taped them down to the back of the pad just after they come out of the sensor and carefully reassembled. Unfortunately, the problem was the same.
I then found this thread in the forum and saw the previous poster's point about the rubber having come loose. Indeed, when it's all put together, and I palm the top of my rubber pad and "wiggle" it, I do find it's noticeably looser than the others. This is clearly a side-effect of having had to man-handle the rubber top off so many times to get at that stinkin' sensor to replace it. I thought I had found the smoking gun, thinking that maybe some wobble coming from that might be triggered by a hit on the adjacent pads, in turn activating the red's sensor. I had my wife "pull down" on those back-mount red's rubber stoppers while I was hitting the blue/yellow since that seemed to stabilize it somewhat. But once again, the double-hit problem remained.
I'm kinda getting short of ideas here. I have one more solderless kit left to try, but I feel like I must be doing something fundamentally wrong that's causing me to burn through them, so I don't want to just attach another one only to find it dead again 2 weeks later. The only thought I have left is that maybe the "wobble" in red's rubber causes the connectors going to the sensor to slowly come loose over time. One thing I notice is that in the original assembly, at the spot where the wires come off the sensor, they're secured to the back of the pad via a pea-sized blob of hardened plastic paste. Obviously I didn't have any of that paste to apply when I was attaching the 1st or 2nd solderless kit, so maybe it places a more important role than I thought. That's kind of what I was getting at when I tried taping down the wires to the back of the pad in my most recent attempt. But if the damage was already done to that particular sensor kit, I can see why it wouldn't have made any kind of difference.
So, yeah, that's the best idea I've got at the moment: Apply my last new solderless kit, taking care to tape it down to the back of the pad from the start. Good idea? Bad idea? Anyone have any other ideas? Yet another idea I have is to wait for Rock Band 3 to come out in hopes that maybe they've got a more robust drum kit design. But I suppose it would be heresy on this forum to talk of switching brands.
