Sequential PROPHET-600 - 6-2 MANUAL MODE; 6-3 RECORD MODE

inputs--on/off for switches, position for knobs—is always maintained in the "Edit"
table in RAM. In Preset mode, the selected program is written into the "Current" table
which controls the synthesizer. If one alters a knob or switch setting in the Edit table,
that change is written to the "Current" table, and will show up as a different sound.
The original program remains unaffected, unless you record the Current table in that
location.
With these basic functions sketched out, we can now turn to specific circuit
descriptions. The hardware is emphasized for several reasons. One is that the software
is proprietary. But more importantly, program details are generally not relevant to
service problems. If you first understand the hardware comprising a specific circuit or
function, you will be able to deduce the important program functions.
Documents referenced below are found in Section 3. (On the schematics, the capital
letters boxed where signals are continued between pages code the sheet on which the
continued signals are found.)
2-1 PHYSICAL ORGANIZATION
Because digital circuits are capable of introducing disruptive and objectionable noise
into their analog neighbors, hybrid design offers some stiff layout challenges. Of
course the Prophet-600 benefits from SCI's experience in this area. It has been laid out
especially with regard for noise reduction. The ground system is a true star
configuration. The controls are wired with separate digital and analog ground and
power supplies on the main control panel. The digital ground connects through PCB 3
to PCB 4. THe analog ground connects directly to PCB 4. The single ground connection
between the electronics and chassis occurs through the AUDIO OUT jack. When
operating disassembled, this connection must be jumpered.
Refer to the interconnect diagram (ID600-1). PCB 1 contains the majority of control
panel circuitry, namely, the LED and switch matrices and POT MUX. The membrane
panel is held to the front panel with its own adhesive. Through the panel, 3101
connects the pad to the switch matrix. NOTE! If the pad malfunctions, check this
connection. PI03 wires-in the keyboard. Of course all of these switch lines are digital.
PI04 is also all digital, conveying the data bus, +5V digital supply (from PCB 3), and a
few chip selects (CS) from PCB3. The wheel cable at P102 carries out +15V and analog
ground to the wheels and returns their two wiper potentials. The analog ground system
in the control panels and the multiplexer output Vmux is brought out to PCB 4 through
TB101. This insures accurate ADC by relieving any ground difference between the POT
MUX and ADC/D AC.
PCB 2 contains a POT MUX plus one extra pot and one switch. Inputs to PCB2 over
TB102/201 are the digital scan lines for this switch, and POT MUX address lines (which
select each pot), plus +5V analog supply and analog ground. The outputs to PCB1 are
the switch state, analog Vmux and the wiper voltage of the OSC A PW pot.
PCB 3 includes the power supply, computer, and most input/output (I/O) hardware.
P301 connects the power transformer secondary. P302 connects the MIDI jacks. As
mentioned, 3304/P104 carries all the digital control panel data.
For low noise, the data bus itself does not go over to PCB 4. TB302 is a power supply
buss, carrying ♦ /- 15V, -5V, and ground. TB303 transfers fourteen latched bits to the
2-4
TM600A 7/83