
Circuit Description—Type 324
tion plates. C132, in the base circuit of Q143, filters the
Q142 pulses to provide Q143 with an average drive current
proportional to the frequency and amplitude of the in
coming signal.
Filtering capacitors include C129, C 131, C122, C133
and C126. The remaining' capacitors improve high fre
quency response of the circuit. Several of them are adjust
able to permit optimum circuit compensation.
The voltage which is applied to the upper vertical deflec
tion plate is also applied to voltage divider R170, R171,
C127 to provide a portion of the output signal to the
trigger generator circuit.
TR IG G ER G E N E R A T O R ^
General
The function of the Trigger Generator is to develop trig
gers to initiate horizontal sweeps. In EX T H O R IZ mode,
part of the Trigger Generator circuit processes external
horizontal signals for application to the Horizontal Am pli
fier.
Block Diagram Description
Refer to the block diagram contained on the Trigger
Generator schematic diagram page. Signals from the V erti
cal Output Am plifier or the EXT T R IG OR H O R IZ INPUT
are applied to a protection circuit and then to an FET
Source Follower circuit. Trigger signals pass through the
T IM E /D IV switch to a Comparator Amplifier. When the
input signal reaches the voltage level determined by the
(T R IG G E R ) Level control, the voltage out of the Compar
ator Am plifier causes the Trigger Multivibrator to generate
a trigger. The TR IG G E R control can be used to select the
direction of voltage change (+ or — Slope) which actually
causes triggers to occur.
When A U TO operation is selected by the TR IG G E R
control, the Trigger Multivibrator free-runs at one of 3 fre
quencies (approximately 30 Hz, 200 Hz, 2 kHz) as deter
mined by the T IM E /D IV control. Triggers occur more often
at higher sweep rates to maintain a relatively constant trace
brightness regardless of sweep rate. A triggering signal
whose frequency is higher than that of the multivibrator
will override the automatic operation and synchronize the
multivibrator (and therefore the sweep) to the signal fre
quency.
In E X T H O R IZ mode, external horizontal signals pass
through the Source Follower circuit and are routed to the
Horizontal Am plifier by contacts of the T IM E /D IV switch.
Protection and Source Follower Circuits
Refer to the Trigger Generator schematic (and to the
Timing Switch schematic as necessary). Circuit operation
during non-automatic internal triggering will be discussed
first. The output signal from the upper half of the Vertical
Am plifier is connected to a contact of the Trig/Horiz Coup
ling switch. With the switch in either internal position, the
signal is applied to C209. The AC component is developed
across R210 and applied through R212-C212 to the junc
tion of D 213, D214 and Q215. Under normal conditions,
only leakage current flows in the Q215 gate circuit, so no
signal loss occurs across R212. D 213, D214, C212 and
R212 provide overload protection for Q215 during EXT
T R IG OR H O R IZ operation and have no effect upon the
internal vertical signal applied to Q215. Source-follower
action (comparable to cathode-follower action) provides
the signal to a contact of the T IM E /D IV switch. In all
except EXT H O R IZ position, the output of the source-
follower is sent through or around C221 and C223 to the
base of Q231. With the Trig/Horiz Coupling switch in I NT
T R IG AC LF REJ, signals below approximately 15 kHz are
attenuated, to avoid interfering with higher frequency trig
gering operation. During IN T T R IG AC operation, C223 is
bypassed and triggers are generated in response to signal
frequencies as low as 30 Hz.
External triggering can be selected by placing the Trig/
Horiz Coupling switch to either the E X T T R IG OR H O R IZ
AC or DC position. DC triggering is possible only when the
switch is at DC and the T R IG G E R control is not at AUTO.
A t that time, C209, C221 and C223 are bypassed to permit
the EXT DC potential to reach Q231.
The 10X position of the (E X T TR IG OR HORIZ)
A TTE N switch provides a frequency-compensated voltage
divider which increases the E X T T R IG OR H O R IZ INPUT
operating range by a factor of 10, without appreciably
changing circuit input impedance.
When the T IM E /D IV switch is set at the EXT H O RIZ
position, the output of the Source Follower Q215 is discon
nected from the trigger generating circuitry and is routed
through switch contacts to the Horizontal Amplifier. Hori
zontal deflection of the beam then occurs in response to
external horizontal input signals (Trig/Horiz Coupling
switch in either EX T T R IG OR H O R IZ position), and the
horizontal POSITION control. R218 permits a setting of
the voltage at the source of Q215 so that no beam position
shift occurs when rotating the (E X T H O R IZ) VAR control.
Comparator Amplifier
The Comparator Am plifier (Q231, Q239 and associated
resistors) quiescently has the Q231 base referenced to
ground through R230. The Q 239 base is set to some voltage
level determined by R246 (TR IG G ER LE V E L), R242 and
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