Theory of Operation—2213 Service
Q703 is one-half of a differential amplifier composed of
Q703 and Q706. The base of Q706 is referenced to ground
through R706. Transistor Q708 amplifies the output signal
from the collector of Q706 and applies it to the drain of
FET Q714. A feedback network composed of R709, R708,
and C708 is connected between the collector of Q708 and
the base of Q703. The feedback network sets the overall
gain of the X Y Amplifier, with X-Gain potentiometer R709
adjustable to obtain the exact gain required.
The X-Axis signal passes through FET Q714 and is
applied to the base of Q731 in the Horizontal Preamplifier.
Horizontal positioning current on the base of Q730 is
added to the X-Axis signal by the action of the differential
amplifier. Then the sum of these two currents is amplified
by Q736 and applied to the input of the Horizontal Output
Amplifier.
Horizontal Output Amplifier
The Horizontal Output Amplifier converts the single-
ended output of the Preamplifier into the differential
output required to drive the crt horizontal deflection
prates. The output stage consists of an input paraphase
amplifier and an output complementary amplifier.
Horizontal signal voltage from Q736 is applied to the
base of Q763. The base of the other transistor (Q753) in
the paraphase amplifier, is biased through a voltage divider
composed of R758, R757, and R756. Horizontal centering
between the XI and X10 Magnified sweeps is accomplished
by adjusting Mag Registration potentiometer R758.
Gain of the paraphase amplifier is determined by com
ponents connected between the emitter leads of Q763 and
Q753. The exact gain is adjusted by Horiz Gain potenti
ometer R752.
Transistor Q747 supplies the emitter current to both
Q763 and Q753. The horizontal portion of the Beam Find
circuitry affects the available current to Q747. Normally,
—8.6 V is applied to the emitter of Q747 from the BEAM
FIND switch via CR745 and R746. When the BEAM FIND
push button is pressed in, the direct —8.6 V is removed.
In this condition, —8.6 V is supplied via R745 which
reduces the current available, thereby reducing the output
voltage swing capability of Q763 and Q753. Diodes CR772,
CR782, CR783, and CR773 prevent the paraphase
amplifier from overdriving the output amplifier stage when
the X10 Magnification feature is in use.
Final amplification of the horizontal deflection signal
is provided by the complementary-pair output stage. Both
sides of the differential output amplifier are identical in
function, so only one side is discussed in detail.
Transistors Q780 and Q785 form a cascode feedback
amplifier. Gain of the stage is set by feedback resistor
R785, and high-speed compensation is provided by C783
and adjustable capacitor C784. For dc and low-frequency
components of the horizontal deflection signal, Q789 acts
as a current source for Q785. High-frequency components
of the signal are coupled through C789 to the emitter of
Q789 to speed up the output response time.
Emitter voltage for both Q780 and Q770 is supplied by
a circuit composed of Q765 and associated components.
The emitter voltage is maintained at a level that provides
proper biasing for Q763 and Q753. Diodes CR770 and
CR780 set up an emitter-bias difference between Q780 and
Q770, causing the base voltage of both transistors to be
equal.
POWER SUPPLY
The Power Supply circuitry converts the ac-source
voltage into the various voltages needed for instrument
operation. It consists of the Power Input, Preregulator, and
Inverter circuits (which drive the primary of the power
transformer) and other Secondary circuits (which produce
the necessary supply voltages for the instrument).
This instrument has either the Current Limit board (A19)
or the Preregulator board (A18) installed as part of the
power supply. Refer to the appropriate circuit description for
your particular instrument configuration.
NOTE
Instruments with a S N B 02 0100 o r above contain the
Preregulator board. Som e instruments below this
serial number were built containing the Preregulator
board. To determine if yours is one o f these, look to
see if there is an Option 4 8 sticker attached to the
rear o f the instrument, if there is not an Option 48
sticker attached and the serial number is below
B020100, your instrument contains the C urrent Limit
board.
Current Limit Board Configuration
The Power switch (S901) connects the line voltage to the
instrument through line fuse F901 and transient suppressor
VR901. Suppressor VR901 protects the instrument from
large voltage transients. High-frequency line noise is attenu
ated by C901.
The Preregulator circuit converts the ac-power-source in
put voltage to a regulated dc voltage. A triac is used as a
switch to conduct current during a controlled period of the
inpuWine-voltage cycle so that energy to be used by the
Inverter circuit is stored in capacitor C937.
3-22
REV NOV 1982
To Next Page
Loading...
Need help?
General
