Marantz SA-12S1, Руководство по обслуживанию

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9. Circuit-, IC descriptions and list of abbreviations
9.1 SAA7399 (MACE2) General.
Mace2 is a name used for the successor of the ACE1 IC. The
term MACE (mini-ACE) is used because MACE2 does not
have a decoder on board. Application area's: Mainly CD-
R(W) and prototyping of DVD(-ROM) or high speed CD-
ROM.
Functions implemented on-board of MACE2:
A further improved digital servo module. Derived from the
ACE1 servo module, but with improvements (make the input
switchable between diode signal and error signal processing,
improved brake).
The 80C51 micro-controller with external ROM.
The OPC. Optimum Power calibration, used for CDR.
The PCS. Position Control Sledge. A way to speed up sledge
movement using hall sensors.
Figure 9-1 Overall block diagram MACE2.
9.2 Features
• Focus and Radial servo loop.
• Built-in access procedure.
• Selectable servo error or servo diode inputs.
• Focus noise performance equivalent to DSICS
• Automatic closed loop gain control available for focus
and radial loops
• High speed track crossing velocity measurement > 350
kHz.
• Fast Radial Brake circuitry.
• Sledge motor servo loop, with pulsed sledge support and
PCS
• Incorporated micro-controller equivalent to 80C51
--> 66MHz.
• Programmable wait state controller.
• Two embedded RAM's of 416 bytes and 1.5 kB res.
• Optimum Power Calibration Hardware support up to
write at N=8.
• Debug facilities.
• Memory mapped interface to sub-modules.
• Programmable clock multiplier.
• 8 Multipurpose I/O lines.
• 5 external interrupt lines.
• External Flash ROM support.
• Sledge stepper motor support.
9.3 The Digital Servo block.
In a CD system, there are some 12 control loops active.
About six of them are needed to adjust the servo error
signals, that is once per disc rotation offsets, signal
amplitudes and loop gains (AGC's) are adjusted to enlarge
system robustness and to avoid expensive potentiometer
adjustments in production. The other six loops determine the
laser spot position on the disc in the radial, axial (focus) and
tangential directions. The servo in MACE2 takes care of
these controls.
The servo inside Mace2 also has to take care that the spot
accesses a required position as fast as possible. This access
system consists of two parts, namely the actuator and the
sled, which are within a certain range, mechanically and
electrically independent. So during an access the servo has
to control as well the actuator as the sled.
9.4 Functional description servo
Figure 9-2 Mace2 servo block diagram.
The following functions can be distinguished:
–
A to D conversion: a direct AD-conversion of the diode/
error currents.
– Pulse density D to A conversion: Noise shaper output
stages.
– Control unit: Provides mainly the communication and on/
off functions.
– Focus normaliser: A partial division of focus and sum
signal. Special saturating provisions are included when
dividing through very small numbers.
– Initialisation control: Includes the radial normaliser,
automatic radial offset compensation and level
initialisation for the Track Position Indicator (TPI) for both
diode and error input signals.
– TPI/TL generation and adaptive debounce: Generates
Track loss (TL) which is protected against disc defects.
The TL is made out of the unprotected TPI signal. The
debouncer (with improved debounce times) minimises
the disturbing effect of HF on the TL and Rp crossovers
for the track count circuitry.