Safety Interlock - C.E.C. CH3000 Service Manual

SAFETY INTERLOCK
The Digital Compact Disc Player reads the disc signal by
detecting the laser beam. It must be avoided for the human
body to directly receive the beam. Especially human eyes are
badly affected by the beam. Therefore, the unit is equipped
with an interlock to prevent the unnecessary laser outputs.
The taser outputs are controlled by the injection or cutoff of
the constant voltage source to the laser diode with Pin 27 of
1C105 («PD75208). When Pin 27 is in "L" (Low) level, the laser
emits the beam. When Pin 27 is in "H" (High) level, the laser
does not emit the beam.
Pin 27 is set in "H" level when the unit is loaded with the
disc and it reads the index signals or when the unit is set in
the play mode after that. When the unit reads the index
signals and the following two conditions are met, the laser
1C105
Mechanism
;
253
uPD75208
Upper Limit Pick-up Inner Limit
SWITCH
SWITCH
O62
O O
J e
O 23
O 22
PLAY -
SWITCH
\)
O04
279 ON/OFF SWITCH
emits the beam.
1) When the Mechanism Upper Limit Switch is on.
2) When the Pick-up Inner Limit Switch is on. (The disc tray
is closed.)
3) The pickup is located at the area of the minimum internal
circumference.
After the above conditions are met and the index signals
have been read, the laser emits the beam when the following
two conditions are met.
1) When the PLAY button is pressed.
2) When the PLAY indicator is on.
CONSTANT VOLTAGE
POWER SUPPLY AC POWER SOURCE
AUTOMATIC
LASER
POWER
CONTROL
e
y | (Y) LASER
DIODE
FL101
PLAY Indicator