Sequential prophet 5 - Page 116

15. While holding S103, PS1, press S108, PS6. This activates “special UNISON" mode. Rather than
from U370-7, the UNI CV will now appear through the five KEY CV S/Hs on PCB4. This reduces
resistor mismatch effects in the ten OSC CV SUMMERs on PCB 4.
NOTE: Both the “bias-setting” (PS1/7) and “special UNISON" (PS1/6) modes will remain active
either until power is switched off or the TUNE routine is activated. Since the GLIDE circuit is
connected to the UNI CV S/H, GLIDE will not operate in special UNISON mode. Therefore, if
you hear glide when tuning, special UNISON has not been activated , or has been deactivated
by some other operation.
NOTE: A peculiarity of special UNISON mode is its effect on PRESET. If special UNISON is
activated and PRESET is switched off then on, you must restrike the program select (PS) of what¬
ever patches you are using for tuning. Special UNISON also affects voice assignments, so voices
can only be isolated reliably with the method of muling R416. VOICE LEVELS.
16. Wi th a scope, verify that the ten oscillator bias CVs are active and pure dc at about 2V. The biases
TABLE 4-1
BIASES
OSC
S/H
RESISTOR
1A
U432-7
R499
IB
U431-7
R4102
2A
U432-1
R499
2B
U432-1
R4102
3A
U419-1
R499
3B
U420-7
R4102
4A
U419-7
R499
4B
U420-1
R4102
5A
U430-7
R499
SB
U429-7
R4102
17. For what follows, it will be convenient to key C5 with a footswitch. If available, connect between
the top bus bar section and the anode (non-banded end) of the ninth diode from the top of the
keyboard (E4).
18. As shown in Section 3, there are ten plated-through holes on PCB 4 which hav the individual
sawtooth outputs of all ten oscillators, no matter what the status of the machine. Probe these
holes when tuning with scope or meter.
19. Switch off S211, OSC B SAWTOOTH.
20. Switch off S221, UNISON.
21. Switch on A-440 reference (PS 1/2).
22. With scope, probe U480-7 A-440/NSE BUFFER, and set for stable trace.
23. With scope, probe OSC 1A SAWTOOTH.
24. Key F#2 and trim V1-R411. OSC 1A INIT FREQ, to 440 Hz.
25. Switch off A-440 Reference.
26. Now key CO (which should be about 155.5 Hz), and set scope up as follows: Trigger on the nega¬
tive edge. Set vertical amp to 2V/div., and timebase to 2 ms/div. Set up display one complete
sawtooth, as in Waveform 4-1. Now select xIO (or xS) time-scale magnification, and turn horizon¬
tal position counter clockwise until the falling edge is centered on the screen, as in Waveform
4-2A. On some scopes it may be necessary to adjust the time scale vernier to center the edge.
Increase trace intensity if required to clarify falling edge. With this scope setup, the falling edge
of all octave Cs should be in exactly the same position if the oscillator is in tune.
27. Select patch 5-1 and switch scope timebase to 0.5 ms/div.
28. Probe the OSC sawtooth outputs, key CO, and trim the four remaining R411s, OSC A. and five
R409, OSC B INIT FREQs for centered falling edge.
29. With scope, probe OSC 1A sawtooth.
30. Select patch 5-2 and return scope timebase to 2 ms/div.
31. Alternately key CO and C5 (with footswitch, if used) and trim V1-R410, OSC 1A V/OCT so falling
edge of both notes is centered on the scope. See Waveforms 4-2A and B.
4-10