Sequential Pro One - Amplifier Balance Adjustment; Digital Interface for Computer Control

LFO squarewave output passes through 33 GATEfCLK IN contacts. The CLOCK signal
normally toggles inverter U114-4. If an external audio source has been connected to 57
AUDIO EN (discussed above), -EXT is low, grounding pin 5 through Dl15 and forcing
U114 high, This allows the -AGATE signal from the AUDIO GATE CPR (discussed
above), to toggle inverter UlE4-2. Whatever the source, this output sets or resets the
microcomputesfs internal fjag bit through U 113-13, T 1.
When the Sequencer or Arpeggiator are being used, S125B or S127B hard-synchronizes
the LFO to the GATE. When GATE is low, R 1 10 1 and R 1102 charge (2129, When GATE
goes high, it pulls Q102 base to ground, switching 4162 on, and discharging the LFOrs
timing capacitor (in the same manner as 0SC A is synced to OSC B).
2-15 POWER SUPPLY
The power supply design is straightforward. As shown on the inset on schematic 5D121,
the primary circuitry was originally included on the PCB itself (Revisions 1.0 and 1.1).
This proved to be mechanically unreliable, most frequently resulting in broken power
switches. Section 4 gives the recommend fix for this problem. Current production Pro-
Ones, designated Revision 1.2 have all of the power supply primary circuitry moved
from the PCB to the back panel.
If any regulators are replaced, a complete functional test will be needed. The slightest
change in supply voltage will affect all tuning adjustments and offsets such as the
Final VCA Balance.