Philips PM3208 Service Manual page 24

4 CIRCUIT DESCRIPTION 4-3
4.2.3 Main time-base (MTB) sweep generator
The function of the time-base generator is to produce a ramp-voltage, to drive the
horizontal amplifier. |C603 together with Q611 act as a current source. The magnitude of
the current can be adjusted with S602a, the TIME/DIV switch and with RV614, the
variable control MTB VAR. The ramp-voltage is made in the time-base capacitors
C606-607 by charging these with the current from the current source. As.in the range
iu s...5004s the same currents are used as in the range 1ms...500ms, the capacitor is, at
the lower speeds, increased by a factor of 1000 by shunting C607 with C608. This is
realised with Q607 which acts as a switch, controlled by Q609, D611 and a section of
$602. The ramp-voltage is available at Q606-drain and via Q612 sent to the horizontal
switching circuit. In position "X DEFL" of the TIME/DIV switch, the current source is
switched off. Thus, the time-base capacitor can not be charged and there will be no
ramp-voltage.
4.2.4 Horizontal switching circuit
4.2 HORIZONTAL DEFLECTION