<div>List -</div> <div> </div> <div>I am having a puzzling problem with a M & H BB grand action that I have never encountered.  Complete regulation (w/new shanks& hammers), everything works great with the exception of 3 notes - F6, A#6, G7 -  in the high treble.  I cannot get this to happen on the bench, and even in the piano when the notes are played softly, even in a trill, they perform perfectly.  However, under continuous mf - ff blows, as in tuning, after anywhere from 1 to 10 strikes (letting the key all the way up), the hammer will get caught on it's way back up by the back check, thereby not allowing it to strike.</div> <div> </div> <div>I have tried numerous adjustments to the angle of the back check as well as to the height of check for these 3 notes, to no avail.  Everything seems to be identical to the surrounding notes, including jack reg - both in the window and to the knuckle core -, rep spring strength, key dip, stroke, the arc of the tails, let-off, drop, etc., etc... you name it.  Keys are rebushed and moving freely.</div> <div> </div> <div>If anyone can shed some light on this puzzler I would be most grateful!!</div> <div> </div> <div>Mark Potter  </div>