Horizontal - Tektronix 2215A Instruction Manual

signal is NANDed with the Alt Sync signal by U680A to
clock U670B. Whenever the Alt Sync signal goes LO at the
end of a sweep and the Ch 1 Selected signal switches from
LO to HI, U670B will be clocked. Since only positive transi­
tions on the clock input will cause the flip-flop to change
output states, two A Sweeps are required to cause the flip-
flop output levels to switch. With this switching arrange­
ment, the crt will first display the two A Intensified Sweeps
and then the two Alternate B Sweeps.
B Z-A xis Logic
The B Z-Axis Logic circuitry switches signal current lev­
els to drive the Z-Axis Amplifier for both the B and the A
Intensified Sweep displays. The current supplied is summed
with the other signal inputs on the Z-Drive line.
When the HORIZONTAL MODE switch is in the ALT po-
sition, pin 5 of U665B is HI. The outputs of U670B and the
B Gate signal from the output of U665D together with the
INTENSITY controls determine the intensity of the A and B
Sweeps.
When the A Sweep is displayed, the Q output of U670B
is HI and the Q output is LO. These output levels will bias on
Q680 and bias off Q685. The emitter voltage of Q680 will
reverse bias CR817 to prevent Z-Axis drive current from
flowing through the diode. With Q685 off, additional Z-Axis
drive current to intensify the A Sweep will be supplied when­
ever CR685 is biased off. Since input pin 5 of U665B is HI,
the gate output and therefore the conduction state of
CR685 is determined by U665B pin 4. Whenever the B
Sweep is running, the output of U665D will be LO. This will
cause the output of U665B to also be LO and CR685 will be
biased off. If the B Sweep is not running, the output of
U665B will be HI and CR685 will be biased on. This will bias
off CR816 and the A Sweep will not be intensified.
If the outputs of U670B are set to display the B Sweep
(Q LO and Q HI), Q680 will be biased off and Q685 will be
biased on. The emitter voltage of Q685 will reverse bias
CR816 to prevent Z-Axis drive current from flowing through
the diode. With Q680 off, the B Sweep will be displayed if
CR680 is reverse biased. Whenever the B Sweep is running,
the output of U665D is LO. Diode CR680 will then be re­
verse biased and Z-Axis drive current will flow through
CR817. If the B Sweep is not running, the output of U665D
is HI, forward biasing CR680 and therefore reverse biasing
CR817. No Z-Axis drive current can then flow through
CR817.

HORIZONTAL

The Horizontal Amplifier circuit, shown on Diagram 6,
provides the output signals that drive the horizontal crt de­
Theory of Operation— 2215A Service
flection plates. Signals applied to the Horizontal Preamplifier
can come from either the A or the B Miller Sweep Generator
(for sweep deflection) or from the XY Amplifier (when X-Y
display mode is selected). Sweep switching is under control
of the Alternate Display Switching Logic circuit. See Figure
3-4 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 contained in the Horizontal Amplifier circuit.
Horizontal Preamplifier
The Horizontal Preamplifier selects display modes and
amplifies input signals for application to the Horizontal Out­
put Amplifier.
The A and B Sweeps, selected by U670B in the Alternate
Sweep circuitry, are applied to the emitters of Q742 and
Q732 respectively through gain potentiometers R740 and
R730. The transistors are biased into the active or cutoff
regions by the control voltage applied at the cathodes of
CR732 and CR742. Switching between the A and B
Sweeps occurs within U760, with a negative input at pin 10
or 9 disconnecting the respective sweep from the rest of the
amplifier. The Horizontal POSITION control adjusts the crt
trace position through pin 14. Output bias current levels are
set by R751 at pin 5 and frequency compensation for X-Axis
signals is provided by C751 connected to pin 13.
Horizontal X I0 Gain is set by the resistor network con­
nected between pins 3 and 6. When the X I0 Magnifier is on,
S721 is closed and the timing adjustment is made using
R754. Magnifier registration is adjusted by R749 so that
there is no horizontal trace shift when switching between
the X I0 Magnifier on and off positions.
X-Y Amplifier
The X-Y Amplifier amplifies the Channel 1 signal from the
Internal Trigger circuitry for application to the Horizontal
Preamplifier.
When the X-Y mode is selected, Q737 is biased on to
establish a HI on U760 pin 12 so that the A and B Sweeps
are disconnected from the Preamplifier outputs. The XY sig­
nal line will be LO and Q756 will be biased off to enable the
X-Axis signal to drive the noninverting input of U758. The
output of U758 will then be a function of the X-Axis signal
and the Horizontal POSITION control wiper voltage. The X-
Axis signal gain is adjusted by R760 and the input voltage
from the Horizontal POSITION control at pin 14 is discon­
nected within U760 so that it does not affect the Preampli­
fier output. The input signal at pin 11 from U758 will be
3-13