Kurzweil CUP2, Service Manual

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D-to-A converter
U15 (page 4, zone D1) is a digital-to-analog converter. It connects directly to MARA on the
digital side and directly to the Audio Out header (J11) on the analog side. Ampli
 ers and
reconstruction low-pass  lters are on the Interface PCB. Although U15 is an 8-channel DAC,
only the  rst two channels (L1 and R1) are used in the CUP2.
A separate MUTE signal comes directly from the CPU to suppress pops and clicks during
power-up and power-down. MUTE must have a low logic level (less than 0.8V) to enable audio
on the Interface PCB.
USB Controller
The CPU has an integrated USB controller that can be either Master or a Slave but not at the
same time. Switching circuits (page 4, zone B1) switch between the two functions. In the CUP2,
the actual USB connector is on the Interface PCB and connects to the Engine PCB by two
cables.
MIDI (5-pin) Interface
The CPU has an integrated UART con  gured for standard MIDI In/Out. The actual 5-pin
MIDI connectors and interface circuits are on the Interface PCB. J31 carries standard MIDI
signals to and from the CPU.
Voltage Regulators
The Interface PCB brings in the 15V power voltage from the AC adapter and converts it
to +5V for the digital circuits and +/-8V for the analog circuits. These voltages enter the Engine
PCB on J23 (page 5, zone D1). Note that although the analog power signal names are +12V and
-12V, the actual voltage level is +8V and approximately -10V.
The various large chips on the Engine PCB require several different power supply voltages:
+3.3V (VCC33), +2.5V (VCC25), +1.8V (VCC18), and +1.2V (VCC12). All of these voltages are
regulated by integrated linear voltage regulators.
U23: +5V (VCC) is the source voltage for the VCC33 regulator.
Powers the CPU, MARA chip, and most of the other digital circuits.
U24: VCC33 is the source voltage for the VCC25 regulator.
Powers the Delay RAM for the effects processor in MARA.
U25: VCC33 is the source voltage for the VCC18 regulator.
Powers MARA’’s core logic.
U26: VCC33 is the source voltage for the VCC12 regulator.
Powers the CPU core logic.
Printed Circuit Boards
Engine PCB
2- 4