[HELP] SP1200 reissue - No sound trough MIXOUT output

Whassup MPC & SP gang !

My SP1200 black reissue 7030 doesn't send any audio signal to MIXOUT mono output on CH 1 ,
but it does works trough individual OUT 1 filtered or unfiltered..

i've been using it like that since i got it in 2010
..but it starts to get annoying especially if i use SP without
a 8 chanel mixer.

whats could be wrong with my SP1200 ?
thanks in advance for any thoughts
peace
Jazz