Just got myself a used SP-555. I played with sensitivity of the D Beam but still the synth plays the wrong notes. For example, if I choose chromatic scale, it sometimes skips the right notes and plays whole note steps instead (no matter how slow I move my hand). Or if I choose some other scale, it sometimes plays some chromatics Can anybody please test this to see if it's a bug or is it my unit gone faulty? My runs on V1.03.
but , maybe there's something interfering with the light - dust or muck or something - you might need to open the case to get to the actual lense depending on where it's located (i dunno how the d-beams are built, never seen one closeup) - I'd give it a good clean with 'isocol'/isopropyl alcohol.. also just known as cd/dvd cleaner or glasses cleaner.. it turns into gas so none of it can leave smudges/etc on anything like water or cleaning detergants so its great for this purpose..
Failing that, you could try reinstalling the operating system.
Sometimes it works but for the most part it skips some note(s) of the scale. So playing melodies with hand and make it respond to each note is not possible (regardless the sensitivity setting).
I´ve read people complaining about defective D-Beams on Roland Clan, I think one was about a brand new SH-201 actually. The guy took it apart and provided pics and a how-to IIRC.
That said make sure to adjust the sensitivity (D-Beam section on the manual) and that there´s nothing getting in the way (which in turn is a great trick to get note stability and frees a hand).
I don´t think v1.04 deals with that particular problem, but there´s no harm in updating the firmware.
Aside from using the filter I think the best use I got out of the D-Beam is for triggering the Subsonic FX.