If you have a JX-8P, and haven't repaired the aftertouch feature (or had it repaired by someone else), then most likely the aftertouch feature doesn't work on your synth. Either that, or it is very difficult to get it to "kick in", say applying an ungodly amount of pressure to the keys to get it to work.
There is another guide on the net that explains the following process for the JX-8P, but I am writing my own since I feel that people will benefit a lot more from the extra details and more detailed pictures that I have provided here. I have also brought to light what I believe to be more of a problem with the sensor than the oxidation of the metal; the conductivity of the rubber strips. I am including my findings in step 4 as an optional way of re-conditioning the conductive rubber strips.
Before you begin:
This process will take at least an hour and a half to complete, but a more realistic approach is to set aside an entire afternoon. Especially if you have never disassembled your synthesizer before. Also note that you should be fairly "good with your hands" since certain parts of the process can be nerve wracking and many small parts are involved.
Items to have on hand
Step 1: Disassembling the case
The first thing we need to do is to remove the case screws that will allow us to flip the top up to gain access to the keyboard module. Start by removing the 3 screws on each side cap, then remove the 2 underneath the left hand side, and finally remove the 4 along the bottom edge. Reference the pictures below for screw locations.
Note: This is one MAJOR step that I could not find ANYWHERE on the net.
Step 2: Removing the Keyboard module
Now, we need to remove the 3 remaining screws that hold the keyboard module in place, cut 5 wire ties and disconnect 4 wire connectors. Then, we'll be able to remove the module completely from the housing. Make note that when you re-assemble the keyboard, the GREEN ground wire goes back on the left most screw. See pictures for full details.
Note: Another aspect of the disassembly that I've never seen addressed is the removal of these wire connectors.
Step 3: Removing the keys
At this point, the keyboard module should be out of the synthesizer. Now, we have to flip the keyboard over(I chose to put bubble wrap cushioning underneath mine). We'll need to remove a clear plastic strip from the bottom of the keyboard, then remove the key springs and finally remove the keys themselves. When removing the keys and setting them aside, make sure you keep them in their correct order. Also, it is easier to remove the white keys first since they mate up with the black ones sort of like puzzle pieces. See pictures for details.
Note: Yet another aspect of the disassembly that I've never seen addressed is that the black key springs are different than the white key springs, do NOT mix them up!
Step 4: Removing and cleaning the aftertouch sensor
FINALLY! yes, it is now time to remove actual parts we need to clean. Start by peeling up the upper rubber housing of the aftertouch sensor. Next, remove the foil strip & the conductive rubber strips(5 strips). Be VERY CAREFUL not to bend the foil!
You may use alcohol & qtips to clean the conductive rubber strips, #0000 fine steel wool to polish the foil strip and toothpaste to polish the gold strips. Other guides mention using acetone to clean the gold strips so that will work as well. If you use toothpaste, be careful as it can be messy to work with. Toothpaste serves as a great metal polish if you don't have the real thing. Of course, if it's available to you, you could use an actual metal polish such as "Brasso" as well.
Click here for an optional method of reconditioning the conductive rubber strips
Step 5: Re-assembly ~Final thoughts and tips
Once you have cleaned all parts it is time to reassemble the aftertouch sensor strip & put everything back together. This was the most difficult part of the entire process in my opinion.
Here is my suggestion: put the rubber strips in place, then put the foil piece on top of the strips and finally lay the rubber housing strip upside down along the top of the contact strip right up against the top piece of double sided tape. Then, in one single motion, flip the rubber housing piece over on top of the foil & conductive rubber. It may take more than one try, but this is the best way that I have found to do it. I attempted once to put all pieces inside the rubber housing, then lay it on top of the gold contact strips, but the result was maddening....the pieces just kept falling out when the housing strip was flipped over.
Once you've got the strip into place, you need to glue down each end with a few drops of glue. From here, you just re-assemble everything in reverse order. Here are a few useful tips: