Sequencer and arpeggiatorFirst of all, the sequencer/arp speed is controlled by the speed of the LFO, which is not uncommon on old synths. The triangle output of the LFO runs through HALF of switch S125 (Seq) or S127 (Arp) when these are in active modes. The other half of the switches are connected to the microcontroller, to read the sequencer or arpeggiator mode. From the switch, the triangle wave is connected to the Gate output, and thus controls the gate directly. So, in sequencer or arpeggiator mode, a new gate signal is sent for every cycle of the LFO. The gate signal from the LFO is NOT sent to the Gate out jack. I don't yet know the shape of the LFO-gate signal when it arrives at the gate. It starts out as a triangle wave, but runs through a transistor and a capacitor on the way.
The square wave of the LFO is connected to the microcontroller as the "clock". One can assume that this is used to control the arpeggiator up/down motion and sequencer advance. More on the clock a little later.
The trigger signal is normally controlled from the microcontroller, and is probably syncronized to the clock programatically when the synth is in sequencer or arpeggiator mode.
The clock signal may be overriden by both an external gate input and the -ext and Audio Gate inputs. how the sequencer/arpeggiator works in these cases is unknown to me at the moment.
Gate/Clock input, Ext and Audio gateAn external gate signal input is available. It is connected to the clock input of the microcontroller and not directly to the gate. As such, the fact that the gate signal comes from an external source is unknown to the microcontroller, which is the reason I don't know how the arpeggiator and sequencer act in this mode.
As the ext and audio gate signals are connected to the clock in, the same is true for these. However, if no external gate/clock is connected, one must probably turn down the LFO speed to 0, to prevent the LFO from interfering.