Theory of Operation—2205 Service
U500A has timed out), U500B will clock a LO back
opto the Q output of U540B, allowing the TRIG'D/
READY LED to be extinguished.
X-Y. In the X-Y mode of operation, the XY line is
LO, holding the input of U520A LO through CR521.
The output of U520A via U520B and U520C will hold
U530B set and no sweep can be started.
HORIZONTAL
The Horizontal Amplifier circuit, shown on
Diagram 5 provides the output signals that drive the
horizontal crt deflection plates. Signals applied to
the Horizontal Preamplifier can come from either the
Miller Sweep Generator (for sweep deflection) of
from the XY Amplifier (when X-Y display mode is
selected). See Figure 3-4 for the block diagram of
the Horizontal Amplifier.
The Horizontal Position control, X10 magnifier
circuitry, and the horizontal portion of the Beam Find
circuitry are also contained in the Horizontal
Amplifier Circuit.
X-Y Amplifier
In the X-Y mode of operation, the 7? signal
(buffered by Q736) is low, biasing Q732 in the linear
region. Transistors Q732 and Q737 are a transî™–
conductance amplifier that changes an input voltage
to output current. The input signal is applied through
gain adjust R39S. The X Offset adjustment is R736.
The signal current flowing out of Q737 is fed into the
shunt feedback stage. The sweep is held at a conî™–
stant low output level when in X-Y mode.
When in sweep mode, the XY line is high and
biases Q732 off. that biases Q737 off and disables
the XY amplifier. The XY line also turns on U380B,
thereby not allowing the X axis signal to get to the
amplifier. The sweep signal is applied through R740
and the gain setting resistor (R744) to the Horizontal
Preamplifier stage.
Horizontal Preamplifier
The Horizontal Preamplifier amplifies input signals
for application to the Horizontal Output Amplifier.
FROM
TRIGGER
FROM
SEC/DIV
SWITCH
FROM SWEEP
GENERATOR
X-AXIS
TO CRT
HORIZONTAL
DEFLECTION
PLATES
Figure 3-4. Block diagram of the Horizontal Amplifier.
3-11
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