After learning about the Yamaha DX7 and its meteoric rise in the popular music of the 80s, I became interested in FM synthesizers. The DX7 was by far the most prolific, but Yamaha released many others, both in Keyboard and rackmount formats. I found this DX21, a mid-range 1985 keyboard model, for a good price on shopgoodwill.com. It has 4 operators per voice compared to the DX7's 6. Despite this apparent downgrade, the later successful rackmount TX81Z and the 2015-present reface DX keyboard both share a similar 4-operator architecture, suggesting that 4 is more than enough to explore the world of FM synthesis. The Keyboard arrived a couple weeks later in a crisp, undamaged cardboard box. Unfortunately, this packaging wasn't sufficient, as the keyboard weighs nearly 18 pounds. The right side end cap was shattered. No replacement caps were available, and the injection-molded design could not be easily swapped for some flat wooden ends like many of its contemporaries. I pieced together what I could with some plastic repair epoxy. Then I used layers of epoxy to build up some replacement screw posts and then drilled some pilot holes in the new posts. After a bit of sanding and trimming, the end cap fit nicely on the end, with its damage mostly out of sight. I also took the time to clean the chassis, circuit boards, buttons, and keyboards. Meanwhile, I sought to get the electronics working again. The keyboard arrived with corrupted memory, unable to produce a sound. Thankfully, I found the manual online and was able to do a factory reset. This brought it to life, albeit in a very limited capacity: it could only do an initialized patch (a plain sine wave) and had no preset memory. After some online research, I found that a dead battery was a common culprit, and without it, it would require a factory reset every time it was turned on, and would never hang on to the presets. I ordered a replacement and soldered it in. Thankfully, the old battery had not leaked and caused any other damage. I did another factory reset and then consulted the manual again, which instructed me to reload factory presets from non-volatile memory. Success! I now had a fully functioning DX21. The synth excels in electric pianos, bells, and bass tones. It also reminds me a lot of early 90s video games, as some consoles had Yamaha-sourced fm sound chips. The keyboard is a joy to play, and there is a huge collection of user-generated 4-operator FM patches out there to try out to get you started on making your own sounds. Overall, it feels great to revive a little piece of history and get to know it.