Originally Posted by BDB
Originally Posted by rysowers
Cheating jacks will cause a note to not play, but won't inhibit the key going all the way down. The OP said "Sometimes they don't go all the way down" which means something is intermittently holding the keys up.

That is easy enough to try, so do it. You will find that the hammer not going up will get caught on the backchecks, which keeps the key from going down. This is by far the most likely cause of an intermittent problem than other things, although bad springs or tight joints could also be implicated. Misadjusted backchecks would not be intermittent.

Definitely possible. But snagging jacks can also be intermittent -- depending on key acceleration.

Keith Akins, RPT
Piano Technologist
USA Distributor for Isaac Cadenza hammers and Profundo Bass Strings
Supporting Piano Owners D-I-Y piano tuning and repair
editor emeritus of Piano Technicians Journal