The Poly-61 is a two-oscillator digitally-controlled analog synthesizer that was released just before MIDI became popular. A later version, the Poly-61M, was released with MIDI support.
The successor to the Korg PolySix, its control panel has fewer knobs and relies on selecting a parameter by its number and then changing its value, making it less suited to real-time sound tweaking than the PolySix.
The first oscillator can use a saw, pulse, or PWM waveform, while the second oscillator can generate a saw or square waveform. It uses a pair of NEC D8049C 8-bit processors to control its systems and a set of six SSM-2056 chips to controls its envelopes.
The Poly 61 has a patch memory battery that will leak and cause damage to the CPU board. This battery will need to be replaced at some point. If it's not, it will eventually destroy the circuit board. A standard 3.6v 3-cell rechargeable cordless phone battery is a suitable replacement.