MX100 Follow-up

[Tom Cole]

To update the list about the Yamaha MX100 problem (studio upright with
Disklavier):

I returned to the customer today armed with a long list of things to
look for. Having all your suggestions was very helpful although no one
had the problem nailed. It might have helped the diagnosis if I had
taken DW/UW measurements on the _black_ keys, hindsight being better
than foresight.

The first thing I checked was the case for evidence of a fall and, right
away, I found just that. Someone had left some obvious scratch marks
from sandpaper plus there was orange peel black lacquer over that on the
front surfaces of the cheeks and toes (the case is polished ebony).
After all my careful checking of down-weights and up-weights last time,
I missed this amateurish repair job staring right at me.

Next, I looked very carefully to see if the fall had changed the
relationships between the keys, action and strings. The right cheek was
damaged more extensively - a wider area was repaired - and I had thought
that this might have something to do with the treble keys being harder
to depress. 

But everything looked normal. The dowel capstans were in the middle of
the wip heels from bass to treble. There was no evidence that the keybed
or action support bolts had moved. I removed the action and saw that the
rail was not bent and the little rubber-booted screw, mounted on the
back of the main action rail, was contacting the plate strut (so no
flexing).

After I laid the action aside, I exercised the keys up and down and
found them to be quite free... until I got past the middle of the piano
and noticed that there was some kind of resistance to key motion in the
treble, almost like very tight balance pin holes. But then I noticed the
metal key stop rail which, in the Disklavier, runs directly over the
balance rail between the two rows of pins. As I lifted the bass keys to
check for balance pin hole tightness, I could lift the keys slightly
before they contacted the felt underneath the key stop rail. But in the
treble, there was no clearance at all. Someone had unthinkingly
tightened two of the fixing screws, which bear against coil springs
underneath the rail, too far which caused the keys to bind slightly. (It
was not the usual nut on the bottom, nut on the top design.)

As soon as I backed off the screws a couple of turns, there was
clearance above _all_ of the key buttons, the touch returned to normal
and the customer was happy. 

1 hour of sleuthing and 1 minute of adjustment did the trick. 

Tom
 
-- 
Thomas A. Cole, RPT
Santa Cruz, CA
mailto:tcole@cruzio.com