I’ve had an MM8 for some time now, and just one of the keys has developed a weird fault.  Regardless of how hard you play it, every so often it plays at full velocity.  It used to be fairly infrequent, but now it happens more.

Any idea what could be causing it, it it likely to be something “user serviceable” if I take it apart.  It’s long out of warranty and I’m OK with a soldering iron etc, just don’t have a clue where to look to fix it.

In synths with velocity sensitive keys, each key has two contacts. The velocity is determined by the time difference between when the first and second contacts are closed. When there’s a problem, depending on which contacts might not be closing, the key either doesn’t play at all, plays at a very low velocity, or plays at a very high one.

While sometimes the problem is in a diode matrix, much more frequently it’s just due to some contamination on the contacts. The contacts are typically rubber with a carbon coating, similar to what’s used in a lot of remote controls, bridging a connection on a pc board. You probably won’t need a soldering iron - good mechanical skills to carefully disassemble the keyboard and gently clean the contacts is what’s usually required.

I’d suggest getting the service manual if you’ve never disassembled keys before. They’re usually not too difficult to work on, but often there’s a technique to key removal and replacement which if not followed can lead to broken or bent parts.

Thanks for that, been a busy week so this is my first chance to look for a reply.

Here’s hoping it’s just contacts in need of cleaning. 

I’ll look for the service manual and start from there.

Thanks again.