You can try the DISC command from another sony DVD remote. It is possible this unit will respond to it even though the button isn't on the factory remote.
If that doesn't work it is possible to do via rs-232 but I don't have the documentation with me, I can look it up and post it in a few days. It is possible because it can be done with an Escient DVD manager via RS-232.
There are 10 types of people in this world, There are those who understand binary, and those who don't!
