OBERHEIM SYNTH

i noticed my matrix 6r won't play the 4th voice on certain patches

when i load up patch #88 sparkles (matrix 1000 patch sheet # 388, group synth 2)
i notice the 4th voice won't play

this is strange behavior because all the midi notes are occurring. 
additionally, the voice allocation when i play the same note repeatedly stays on
the same voice

when i change to other patches like say # 90 - stellar*, pressing the same note
repeatedly shows the voice allocation moving step by step from voice 1, 2, 3, 4,
5, 6, and repeating again at voice 1

so why is this happening?

i checked the spillover. stereo, and other master parameters

yes the midi works - you can see the voice allocation light up, but no sound

i can't believe it's a faulty voice chip. if so, why does it sound on some
patches but not on others?

i dug into the programming of the patch and it uses dco sync 2 - patch edit,
parameter 02, dco1 sync 2.

wheni change it to dco sync 1, i can hear a little bit of the voice, and when i
turn it to 0 (off) i can hear the voice completely

so is it dco sync that kills voice # 4? well, so i went to patch # 99 syncage*
and it has dco sync set to soft (patch edit, parameter 02, dco1 sync 2) and all
the voices sound perfectly


so anyone else have this happen?

any explanations?