I recently bought a Piano3 new. I love it!
But after about 10 days of playing for 3-4 hours a day, C5 started making a loud knocking noise when releasing the key quickly. It got progressively worse till it was unbearable to play fast passages without getting bothered by it.
I suppose I could send it back to the store for an exchange or warranty repair, but that will probably only net me another keybed with the same problem and possibly weeks of not being able to play my new instrument. Plus, I wanted to find out what was causing the noise.
I've repaired keybeds on stage pianos and synths in the past so not a big deal for me to open up the Piano3. I don't recommend you fix your instrument on your own as it can void your warranty, but if you do decide to fix it, here is what I did (do at your own risk).
It takes T20 torx screws; just remove the screws along the back, sides, and 2 from the bottom (one is close to the headphone jack and the other near the power switch). I use the Nord's 4 legged stand so the screws on the bottom are fully accessible. Also no need to unplug any of your output, pedal cables. I suppose you might want to unplug the power harness if you feel safer, but not needed.
Once the screws are removed, you can pull up on the panel and undo one ribbon cable by pushing the 2 tabs on the edges with your fingers and set aside the front panel.
I partially disassembled C5 by releasing a tab at the rear(?) front(?) of the key (the tab is pink in color) using a small flat head screw driver and pulling up. The banging noise is coming from the hammer banging back to its resting position upon release of the key. The rubber grommet at the top of the hammer unit appears to deform easily and unless it continues to makes positive contact with the inside of the key, the looseness causes the hammer to bang back to its resting position.
A true fix would be to replace the grommet with a slightly thicker or harder material or add a dampener to the hammer unit itself at the bottom, but that would require a more intense repair so I decided to fix the looseness by adding a shim inside the key.
I used some 2mm thick hard felt cut to about 7-8mm width and about 10-12cm length and placed it inside the cavity of the key (above the hammer's grommet that contacts inside the key). If in the USA, one can source this hard felt "EZ stiffened felt" at craft stores like Michael's Arts and Crafts, Joanne Fabrics. You will want to make sure the hard felt is somewhat loose inside, otherwise it can slightly bind the key. I don't travel with my instrument so I did not do this, but if you do, I recommend you put a piece of tape under the key so that the felt does not accidentally fall out of the cavity while the instrument is positioned in a way the hammers are in a neutral state. For this, I recommend using foil tape.
Re-assembled the key to ensure no noise and no odd friction compared to adjacent keys. It takes a little playing to break-in the hard felt.
My B4 key was also starting to make noise so did the same. It is an easy fix.
Hopefully Nord will come out with a permanent fix for the keybeds, but until then, I know how to fix the noise so more power to me.
My Piano3 was back in service within the hour. Next time I need to service a key, it will take me no more than 10 min to do.