via this auction

"The included Roland D-50 Rescue kit (which also works for the D-550) will also allow you to restore the system settings via MIDI. A printed version of the manual is included; there is no original box. To this day the synth remains popular for its unique and powerful sounds. You will find it is still fully supported (on eBay you can find upgrades for the display and other accessories; the internal battery used is a very common and inexpensive CR2032.
Features:
16 voice polyphony (32 partials with 2 per voice), or 8 voices (using 4 partials per voice in Dual or Split Mode)
Oscillators: Digital (Linear Arithmetic Synthesis) ; PCM,
LFO : (3 x 2 tones = 6 LFOs)
VCF/VCA FILTER: low-pass-resonant; ADSR envelopes
61 note keyboard with velocity and aftertouch
64 patch memory"