I have an Ensoniq ESQ-M, which is the rack-mount version of the ESQ-1. It contains 8 of the 5503 oscillators. This particular unit “mostly” works; I had it apart once (several decades ago), and when I put it back together I had one of the connectors off by one. I corrected the issue, obviously, but now the display is very dim (still working, though), and it sounds as if one of the voices isn’t operational (random notes don’t play when sent a stream of MIDI data). Other than that, I think it’s all good (although I haven’t powered it up in quite some time – the power supply may need re-capping...). I’ve been carting this around for a while now, and would love for it to go to a good home. Let me know where to send it! ~~ Mark Moulding (tyer@att.net)