In this video I show how I replaced all of the front panel buttons in a Yamaha DX7. The buttons I used was Omron B3W-4050 as I had lots of these on hand from previous projects. These are a bit pricey but they are high quality and also sealed so dust cannot get into them. You can probably use any 12x12mm button you find though but check the measurements before ordering, especially the dimensions of the stem. The Omron buttons work fine but the stem is ever so slightly thicker than the original buttons and it’s a _really_ tight fit when you mount the key caps. I have had no issues with the caps cracking or so though. If you are worried about this you can do a cross cut using a Dremel in the stem (see x0xb0x – Replacing buttons with Omron B3W-4050 for details how to do this).
I encountered a small issue when having mounted right side board, some of the buttons were pushed down by the front panel foil. This was probably due to the tight fit of the key caps on some of the buttons; the key cap rode a bit higher than it should. I resolved this by adding a washer between the board and the mounting post for each screw. This gives the button 0,5mm more space and then everything worked fine.
I tested the buttons using the built in test mode in the DX7; there is a separate test mode there for testing all of the switches on the front panel. You can enter the diagnostic mode by pushing the Function, #16 and #32 button at the same time and when all the buttons are pushed release them. For more information about the test mode please see http://yates.ca/dx7/DX7%20System%20Test%20Routine.docx