<html> Interesting about the plastic jacks, though I don't see what difference it would make. For some kind of relief, you might try repinning the hammer flanges firmer. Also make sure there isn't a rail set up to stop the motion of the jacks too soon. If it's still driving you crazy, you might widen the letoff a hair, and maybe strengthen the hammer springs a little bit. Good luck - I've seen this on Yamaha big uprights and also on Kawai big uprights, though not all of them, or this bad. For some reason, I haven't found it on consoles or short uprights. Maybe I just didn't look ... Susan At 11:04 PM 7/11/2005 -0700, you wrote: <blockquote type=cite class=cite cite>Greetings --   I did a dealer prep on a brand new, fresh out-of-the-box, Yamaha MX500 P upright today. Every single note double-struck when played softly. I checked regulation and had to adjust lost motion on every key. Let-off also needed to be adjusted, but only on about 10 keys. When I finished these two adjustments the regulation may not have been perfect but it was certainly close enough. Still, every single note was double striking when played softly. (Definition of "softly": Playing the note faster then when you are checking let-off but slower than it takes to actually check.)   What I am witnessing is this: When I play the note, just before the jack releases from under the butt the hammer jumps off the jack prematurely and strikes the string. After striking the string the hammer then bounces back onto the jack, which is still in it's pre-release position. Continuing through the keystroke results in the hammer striking the note a second time as the jack finally releases from under the butt.   This was something new to the store manager so I called an associate. He suggested I go through the routine I had just completed, but otherwise could offer no further suggestion. OK, so I decided to tune the thing while I pondered the matter further.   Aha! Tuning finished. Let's see what the other Yamaha uprights are doing. I checked six other, (not used), Yamaha uprights on the floor, (none of which I had prepped, but all of them allegedly prepped), and every single one of them exhibited the same double-strike behavior. For comparison I then checked some NON Yamaha uprights and they all behaved properly. I finally checked the showroom Yamaha action model, and it, too, was behaving correctly. BUT... It was then that I noticed that all the Yamahas used in this test had plastic jacks. The Yamaha action model, as well as the non-Yamaha uprights used in this test, all had wooden jacks.   That's all the clues I have. Anybody have any idea what's going on, and what can be done to correct it?   Geoff Sykes Assoc. Los Angeles Chapter</blockquote></html>