I repair them to keep them in play, impossible to get some of the parts so I tend to use one that is too far gone to repair a number (usually three or so) of others and then I still end up with some more spares that might come in handy later.

They are incredibly durable, one that I got had been in a fire but it still worked, even though more than half of the keyboard had been burned off. The mainboard went on to repair one that was otherwise good but had a fried CPU. Another one I got had been owned by a touring musician, who apparently didn't know about flight cases :) There wasn't a lick of paint on the outer case. I got it for free because it wouldn't turn on any more. Turned out that the voltage selector had somehow been moved in transport and got stuck between the two settings, leaving it disconnected. That was the fastest fix ever, there simply wasn't anything wrong with it. (And good thing that voltage selector had not been pushed a tiny little bit further because then it would have been end-of-story for sure).

So, I have a pretty large collection of spares, looms, main boards, display boards, keys (they do break, especially as the plastic ages it can get more brittle, more so in synths that have been in the sun), switches, PSUs and so on. Every now and then I put an ad out to get people to sell me their broken ones or to help them out and then a new batch of working DX-7's goes back into the world. It's never going to make me a dime, especially not when counting the time but it feels pretty good to keep these oldies alive, and to see how happy musicians are when their baby works again.