The MX-100 Disklavier is built around a Yamaha U1, an excellent studio
piano.  Assuming that the piano can be put into top shape and hasn't
been abused, $4000.00 may be a fair price.  The U1 is notorious for
those horrible brass wheels that seem to do everything but rotate.
Replacing them with larger double rubber wheels, (faultless), would
be advisable.

The MX-100 has been out of production for many years and was part of
the first generation Disklaviers.  With some possible exceptions Yamaha
no longer has parts for them.  Their most common failure are the driver
boards, which consist of a series of rectifiers that feed the solenoids.
I had a bad board in one once and literally purchased the last one that
Yamaha had in their inventory.

The rectifiers themselves can be replaced if you are handy with a
soldering iron.  It will play if one or two are bad but if several are
bad it will shut down entirely after a minute or two as part of a
built-in safety feature.  If the system seems to play okay as it is
I would suspect it may be a fair deal.

Rob Goodale, RPT
Las Vegas, NV