ALPHA 5 CD SERVICE MANUAL
Si/RD: On/off control for the focus servo system. This line is continuously made low by the SERVO-uP during
the stop condition. At starting up, the SERVO-uP forces this line in a high-Z state. In this case the focus servo
system is enabled. After some time the Si/RD-signal is made low for a short period to indicate that the focus
servo is ready.
TL: Track loss. This signal is made low by the TDA8808 as soon as a track is lost.
REdig: Digital radial error signal (Re2 - RE1 ).
BO:
B1: Input control bits for off-, catch-, play-status and
B2: DAC-output-current for radial motor. B3:
RE:
1
/2 bit DAC. This signal is normally held high-Z by the SERVOuP.However when TL goes low the RE line
can influence the proportional amplification of the radial servo (improved S-curve).
CRI: Counter reset inhibit. This signal goes low during a real track loss (>600us) or during execution of a jump
command. When low, this signal allows the divide-by-588 master counter in the DEMOD timing of the SAA731 0
to run free. The signal becomes high during initialization of the "catch" status of the radial servo.
DODS: Drop-out detector suppression. This signal is externally hard wired with the CRI-
signal.
QRA:
QDA: Subcode channel.
QCL:
SWAB/SSM:Subcoding word clock and start/stop turntable motor. This line is continuously made low by the
SERVO-uP during the stop condition. At starting up the SERVO-uP forces this line to the high-Z state. In this case
the turntable motor is started and the subcoding word clock is connected to this line by the SAA731 0. If this
line is forced low by the SERVO-uP, a motor stop condition will be decoded by the SAA7310 and fed to the
turntable motor control logic circuit.
MC: Motor speed control. The SERVO-uP uses this line to measure the turntable motor starting up time. This is
necessary for the 8cm/12cm disk identification and for the software controlled brake of the turntable motor.
TEMP: Motor offset and bandwidth switch. At starting up the turntable motor, the SERVO-uP measures the
starting up time (cfr. MCES). If this time is small (small moment of inertia), the TTMO line it turned high by
the SERVO-uP. If this time is long (high moment of inertia), the TTMO line remains low. As the TTMO line is
switched high the DC amplification is lowered and an offset is injected to the turntable motor circuit.
ALPHA 5 CD SERVICE MANUAL
Power Supply
The mains input to the unit may be 230V or 115V, selectable by insertion of the appropriate fuse.
This unit does not have a mains on-off power switch. Instead there is a 'Standby' switch (SW402)
which turns off the power to some parts of the circuit (decoder, digital filter and display) and puts the
main microcontroller into a reset condition.
Two separate windings on the secondary provide isolated digital and analogue power supplies.
The digital supplies consist of +10V & -10V unregulated to power the servo drivers and motors and
+5V (Z402) and -5V (Z403) for the critical signal processing and microcontrollers. Two other taps on the
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