Yes. Notes "losing their velocity sensitivity" denotes a broken key. Just because the returns and appears normal, you haven broken that Key when it appears that it is "losing their velocity sensitivity". This happens most often when the appropriate velocity curve to match the playing style of the performer is not selected.

Overall Yamaha keyboards are among the sturdiest available. Go check with your local authorized repair location... they should be able to give you all the gorey details. Don't judge by your own misfortune alone.

Appropriate velocite curve is not selected?
Striking the keys made small holes into the rubber strip under them. It has been replaced, should work fine..
To prevent this from happening on my new MOXF, should I set the velocity curve to Soft? This setting should allow me to play harder samples on softer key strike...

I own Yamaha DX7, the keyboard is still fully functioning! After those years it's almost unbelievable! Very robust instrument!

Sorry, I didn't see your follow-up.

The velocity curves work so that those who tend to be heavy-handed, and there is nothing wrong with being heavy-handed unless you are unaware that you are...

Placing the overal Velocity Curve = Hard means it will take more effort to get loud
Placing the overall Velocity Curve = Soft means it takes less effort to get loud

The concept is to not reach 127 until you use the absolute maximum effort you will use. There is never a reason to hit the keys harder than it takes to reach 127... that's all there is in MIDI.

If you're hitting the keys and reaching 127 you have to realize that hitting them any harder does not achieve anything but wearing out your Key bed quicker. There is going to be a time, eventually, when any mechanical mechanism will wear out - you can maximize your keyboard's performance by not hitting it harder than it can give results. The way to do that is to ipunderstand Velocity and Volume.

From years as a recording engineer/musician I've learned that the proper listening level is vitally important from both the standpoint of the *comfort of the player* and the *recorded results*. If your sound system is up too loud, you naturally play with less effort- if your system is too low in volume, you naturally increase the effort with which you attack the keys.

And this has many levels of subtlety... like a person with headphones tries to talk to you, naturally starts to talk loudly... it's because they adjust their volume with just the internal ear, instead of both internal and external. The headphones block the important external volume level, so they don't even realize they are shouting at you. It feels normal to them to shout under those conditions.

The same thing is in play when listening to yourself through speakers... too soft, you start physically playing harder, and if too loud, you back off... at either of the extremes you start to complain... but there are many levels of subtlety involved. Finding the right balance of velocity curve and resulting volume level, is not only important for your musical results, it can impact the length of time your keyboard action lasts.

That said, the actions are designed to last. But mileage varies depending on how it is used. The Yamaha FS action from the DX7 lasts seemingly forever for some, others wore it out... that's because there are so many different players and some never hit the balance right of the curve and output volume.

Not only is there a overall Velocity Curve, each sound is customizable within the synth. Once you begin to analyze your playing versus the velocities you are generating, and once you recognize how important it is to listen at the appropriate volume in the room or Phones, you start to have less wear and tear on the Keys and the underlying sensors.

The updated FSX action is currently found in the Montage 6/7, Tyros5-61/76.
The MOXF6 had a specially made action, the MOXF8 uses the Yamaha Graded Hammer action.