This DX7 is fully functional and in good condition. This one features a mod that adds 3 additional banks of 32 patches for a total of 128 patches of internal memory. Just hold the Operator Select button while pushing button 1-4 to select bank. The mod also implements a few other utilities like keyboard split, velocity offset, & local keyboard on/off accessible in the Function menu under button 13.
One of the most popular digital synths ever was the DX7 from Yamaha, released in 1983. It featured a whole new type of synthesis called FM (Frequency Modulation). It certainly is not analog and it is difficult to program but can result in some excellent sounds! It is difficult because it is non-analog and thus, a whole new set of parameters are available for tweaking, many of which seemed counter-intuitive and unfamiliar. And programming had to be accomplished via membrane buttons, one data slider and a small LCD screen.
Still the sounds it shipped with and that many users did manage to create were more complex and unique than anything before it. Percussive and metallic but thick as analog at times, the DX7 was known for generating unique sounds still popular to this day. The DX7 was also a truly affordable programmable synth when it was first released. Almost every keyboardist bought one at the time making the DX7 one of the best selling synths of all time!