Philips PM 3210 Operating Manual page 10

10
Ill. Description of the block diagram
Y-AXIS
An input signal applied to socket Ya or YB is fed to
unit | or unit 2. These units are identical and contain
the following circuits: an input step-attenuator,
a protection circuit, a pre-amplifier and a drift-compen-
sation circuit, the continuous attenuator and the gain
pre-set control.
The protection circuit prevents damage to the input
field-effecttransistors by too high an input voltage.
The drift-reduction circuit reduces the drift inherent in
the high sensitivity of the amplifier.
Via the delay line the signal is fed to the intermediate
amplifier on printed-wiring card 4.
Printed-wiring card 4 comprises four main parts:
1. an intermediate amplifier receiving the signal from
the pre-amplifier of channel A.
2. anidentical amplifier for channel B. These two ampli-
fiers are equipped with shift and polarity controls.
3. the diode switch, which is controlled by the switch-
driver circuit.
4. the Y output amplifier that feeds the signal to the
vertical-deflection plates.
TRIGGERING
The triggering signal from the pre-amplifier of channel A
or B, or from an external source can start the time-base
generator (unit 3).
TIME BASE
The time-base unit is provided with an optional auto-
circuit that makes the time-base generator free-running
when there is no triggering signal.
The time-base unit supplies the following output
vol tages:
1. a sawtooth voltage. Via the printed-wiring board this
sawtooth voltage is fed to the X-amplifier unit 7 and
toa socket on the rear panel of the instrument.
2. a gate pulse which is fed to combination unit 8 via the
printed-wiring board. This gate pulse controls the
unblanking of the c.r.t. during the sweep.
3. analternate pulse. This pulse controls the switch
driver unit 5, which in its turn controls the diode
switches.
X-AXIS
The X amplifier consists of three parts:
1.
i)
the time-base amplifier. This amplifier feeds the saw-
tooth voltage from time-base unit 3 symmetrical and
amplified to:
. the diode switch which, as dictated by switch driver
unit 5, connects the time-base signal or the signal from
channel B to:
. the X-output amplifier which feeds the signal to the
X-deflection plates of the c.r.t.
DIODE SWITCH
The diode switch is part of the horizontal as well as of
the vertical path and can, together with the switch driver,
accomplish the following situations.
1. Channel A is connected to the Y output amplifier and
the sawtooth voltage from unit 3 is fed to the
X-ampilifier.
. Channels A and B are in turns connected to the Y out-
put amplifier for approx. 1000 ns (position
CHOPPED). The sawtooth voltage from unit 3 is
connected to the X-amplifier.
. Channels A and B are alternately connected to the
Y output amplifier at every fly-back of the time-base
sweep (position ALTERNATE).
The sawtooth voltage from unit 3 is fed to the
X-amplifier.
. Channel B is connected to the X output amplifier and
channel A to the Y output amplifier (position X-Y).
In this position the bandwidth is limited in the
Y output amplifier. The bandwidths of the two
channels (A vertical and B horizontal) are now the
same (5 MHz at a phase difference < 2°),
. Channel B is connected to the Y output amplifier, the
sawtooth voltage from unit 3 is fed to the X-amplifier.
SWITCH DRIVER
The switch driver unit 5 consists of the following parts.
1.
2.
a push-button switch, which enables the switching in of
the positions described above.
a blocking oscillator which oscillates at a frequency of
about 2 MHz, in position CHOPPED.
In position ALTERNATE the blocking oscillator is
triggered by the alternate pulse. Triggering is such that
the oscillator supplies a pulse at every fly-back of the