Tektronix 2230 Service Manual

Theory of Operation— 2230 Service
HORIZONTAL
The Horizontal Amplifier circuit, shown on Diagram 7,
provides the signals that drive the horizontal deflection
plates of the crt. Signals applied to the Horizontal
Preamplifier may come from either the A or the B Miller
Sweep Generator (for sweep deflection) or from the XY
Amplifier (when Nonstore X-Y display mode is selected). A
and B Sweep switching is controlled ty signals from the
Alternate Display Switching Logic circuit discussed earlier.
Either the Nonstore sweeps or the Storage horizontal
deflection signals are passed to the Horizontal Output
Amplifier via a diode gating circuit. Signal selection by the
Horizontal Mux circuit is controlled by the Channel Switch
Logic output signals (located on Diagram 2). See Figure 3-
6 for the block diagram of the Horizontal Amplifier.
The Horizontal POSITION control, X I0 Magnifier cir
cuitry, and the horizontal portion of the Beam Find circuitry
are also part of the Horizontal Amplifier circuitry.
Horizontal P reamplifier
The Horizontal Preamplifier switches the Nonstore hor
izontal drive signals and amplifies input signals for applica
tion to the Horizontal Output Amplifier.
The A and B Sweeps are applied to the emitters of
Q732 and Q742, through Sweep Gain potentiometers
R730 and R740. Switching of the A and B Sweeps is con
trolled with these transistors. Using the A DISP and B
DISP signals obtained from the Alternate Display Switch
ing Logic circuitry (Diagram 6), 0732 and Q742 are either
biased into the active or cutoff regions via CR732 and
CR742. The POSITION control (R726) horizontally adjusts
the crt trace position by supplying a variable dc offset volt
age, through pin 14, to the output of the preamplifier. The
position offset voltage from the wiper of R726 also goes to
the Vector Generator circuitry (Diagram 20) to horizontally
position the STORE mode waveform displays. Readout
displays are not affected by the Horizontal POSITION con
trol. Preamplifier output bias current levels are set by
R751 at pin 5, and frequency compensation for X-axis sig
nals is provided by C751, connectd to pin 13.
Nonstore horizontal XI0 Gain is set by the resistor net
work between pins 3 and 6 of U760. When the X I0
Magnifier is on, S721 is closed, and the amplifier gain
increases by ten times. Magnified timing accuracy is
adjusted using X I0 Gain potentiometer R754. MAG REGIS
potentiometer R749 is adjusted for no horizontal shift at
the center of the graticule as X I0 Magnifier is switched on
and off. A second set of contacts on S721 informs the
Microprocessor whether X I0 Magnification is off or on.
The SEC/DIV readout is automatically set to the correct
scale factor, and STORE mode waveforms are digitally
modified to reflect XI0 magnification.
X-Y Amplifier
The X-Y Amplifier amplifies the Nonstore Channel 1 sig
nal (X-AXIS) from the Internal Trigger circuitry (Diagram 4)
and passes it to the Horizontal Preamplifier.
When the Nonstore X-Y mode is selected, Q737 is
biased on 1o place a HI on U760 pin 12 to internally
disconnect_the A and B Sweep and the HORIZ POS input
pins. The XY signal line is LO, biasing Q756 off to let the
X-AXIS signal drive the noninverting input of U758. The
output of U758 is a combination of the X-AXIS signal on
pin 3 and the Horizontal POSITION voltage applied to
pin 2 via R758. The X-Axis deflection accuracy is adjusted
by X-GAIN potentiometer R760. The single-ended X-AXIS
signal at pin 11 of U760 is changed to a differential signal
at the preamplifier output pins. The differential signal is
passed through the Horizontal Mux circuit to the Horizon
tal Output Amplifier for final amplification. When the X-Y
mode is not selected, Q756 is biased on, and the X-AXIS
signal is shunted to ground through the transistor.
Horizontal O utput A m plifier
The Horizontal Output Amplifier provides final
amplification of the horizontal Nonstore sweep signals or
the Store mode deflection signals to drive the horizontal
crt deflection plates.
In NONSTORE mode, signals from the (+) and (—)
SWP outputs of U760 drive the Horizontal Output
Amplifier. In STORE mode, horizontal LH OUT or RH OUT
deflection signals are passed through the diode gate to
drive the amplifier. Drive signals for STORE mode and
readout character displays are selected by the Display
Controller. Either Nonstore sweeps or Store deflection sig
nals are selected by the diode gating using signals from
the Store/Nonstore Multiplexer (U7201 on Diagram 2)
through inverters U7202A and U7202B.
The selected signals drive a differential shunt-feedback
amplifier. Due to the feedback, the input impedance of the
amplifier is low. The base voltages of Q770 and Q780 are
biased at nearly the same dc level by forward-biased
diodes CR768 and CR768 located between the two
emitters.
REV DEC 1986
3-23

Tektronix 2230 Specifications

General

Brand	Tektronix
Model	2230
Category	Test Equipment
Language	English