Help with Prophet T-8: top octave not triggering properly
2009-05-06 by r_j_d_2.phila
hi folks, im hoping you may be able to provide some insight into my issue. i have uploaded the schematic of the board in question(008-9B); the two files named "38" and "39" are for this Optical board. this is the only board that attaches to the keyboard assembly, so i have to assume it is responsible for encoding the keyboard triggering. the problem: the top octave does not trigger properly. if played staccato, NONE of the notes trigger, EVER. if 4 notes are played legato(sustained), and the 4th note is ONE HALF STEP away from the 3rd note, it will trigger, and HANG. i can play as many whole step intervals as i want to, and NO notes will trigger. 4 adjacent 1/2 steps will trigger, and hang, the 4th note. bottom line: the top octave is screwy. because of its construction, its impossible for me to access the pins of the IC's on board 008-9B while the machine is on. when i take voltage readings on output pins that lead to 008-9B's connector harness, i get change in activity for the triggering notes, but none for the non-triggering notes. can anyone do a once-over on the IC's of this board, and at least GUESS if the problem is likely on this board, or elsewhere? thanks much for your help-rj