Some Touch sensitive keys lost sensitivity

[Naddew]

Hi

 

We purchased an old Casio WK3700 second hand.

After a day of playing, 2 sets of 8 contiguous keys changed their behaviour. When you touch the keys even slightly they hit as if you have hammered them. But only these two sets of 8. After a break they worked again for a bit. Then it failed again and I've not seen it work since. The key will hit hard even if you touch it slightly. Once touched, it will stay on until you power cycle. If piano it will not make a sound once sustain has expired, if an organ it will sound constantly.

I have taken it apart, cleaned it up etc. Swapped the rubber boots around but still these same two sets of 8 are failing.

One set of 8 is near the bottom, the other is about 3/4 way up. Both start on a B.

Looking at the circuit boards, there are 2, the two sets of 8 are on different boards. Each set of 8 shares a common channel/wire which I've traced both of back to the main board via the ribbon cables and can put a DMM from the key pad to the main board with minimal resistance.

I've not yet worked out the path of the other side as it's a bit of a maze.

I figure as these are perfect contiguous sets of 8 that has survived a clean and a switch of boots, that also lines up with the electronics of shared wires it is probably not a physical problem with boots or contacts or dirt. 

 

Any ideas of what might be the issue here? It seems like a great keyboard for its age and my 12 yr old son is very exited to get it working!

 

Many thanks.