1980s Yamaha TX7 FM Synthesizer FM Expander Module

Tested in good working condition, shows average cosmetic wear. 

More info from VSE:

The TX7 is essentially a non-rack-mountable desktop module form of Yamaha's DX7 FM synthesizer. Editing can not be done from the front panel, but must be accomplished externally via MIDI using either a DX7 keyboard.

Software such as Unisyn can be used to edit the parameters of the TX7. There are only 32 patches for storing any sounds as on the DX7. It's probably better to collect patches from the internet to expand your library of sounds since FM patch-editing is difficult enough on a professional DX synthesizer. Aside from its limitations, the TX7 is an affordable way to get your hands on original DX7 sounds.