ROLAND RD-600/500 key fix
*may apply to other Roland pianos as well*

to open the "hood" - remove the 3 screws on each side of the RD600 and remove the screw in the middle (7 screws total) - now you can flip open the "hood"
with the top flipped open you can now check for loose connections on the rear panel and also confirm that all other connections to the circuit boards are well connected / make sure the screws on the power supply are tightened properly as well / If you need to remove the entire keybed, then remove the metal plate in front of the keys. Otherwise, if you just want to remove a key and hammerweight, you don't need to remove this plate. / start by removing the 2 screws on each side of the metal bar
remove the 7 screws that hold the metal bar in place

 
with the metal bar removed, you can now remove any built up dust and dirt around and under the keys

 
with your finger, gently push apart the plastic tabs where the key is connected to the board just enough so that you can pop it out and remove the key / it won't take much pressure to do this - be careful not to apply too much pressure and break the plastic tabs

 
with the key removed, now remove the hammer weight (highlighted in green here) by simply lifting it out of the housing / the same procedure applies to the black keys as well, the only difference is that the hammer weight on the black keys is shaped a little different than on the white keys / you can now inspect the key and the hammer weight for damage and wipe clean any built up dirt and grease
The most common problems in my experience are the following:
 
A: the little plastic tabs break off / symptoms of this are lower key height and keys that do not come back up / most of the time the broken piece can be found right where it broke off in the housing as the grease holds it in place/ clean it off and carefully glue it back on the key with Super Glue or the like / this fix usually will be permanent if you glue properly but not a bad idea to replace the key in the future
 
B: The hammer weight has cracked and/or broken apart / symptoms of this are sluggish response and a "knocking" noise when the key is pressed / you can glue this back together but in my experience this fix doesn't hold very long before it breaks apart again / I recommend replacing this piece
 
C: In the worst case scenario, if you don't find anything broken on the key