Tektronix 7623, Instruction Manual

Page: 66 / 266

Circuit Description —7623/R7623 Service
Horizontal deflection
signal to right
deflection plate
of CRT
Horizontal deflection
signal to left
deflection plate
of CRT
Fig. 3 19. Horizontal Amplifier detailed block diagram.
limit the current to U510. At the same time, current is
added through CR531 and CR532 from the display limited
current line. This added current maintains about the same
DC currents through the output circuit in both positions of
the BEAM FINDER switch. The signal at the output is
connected to the right and left amplifier inputs. Resistor
R525 adjusts the amplifier for center screen deflection in
the absence of an input signal to U510.
Output Amplifier
Transistors Q539, Q551, Q558, and Q560 function as a
current driven feedback amplifier. The input current is
converted to a voltage output signal to drive the right
horizontal CRT deflection plate. R558 establishes the
quiescent current level for series connected transistors
Q558 and Q560.
The CRT deflection plates present a capacitive load to
the amplifier, which requires additional current during fast
transients. Extra current for positive excursions is provided
by Q551 via R555, C555, and Q558; for negative excur­
sions, by Q560 via R563.
Resistor R556 reduces the power dissipation in Q558.
Resistors R566, R567, and R569 provide DC feedback and
establish low frequency gain. Capacitors C566 and C588 are
adjusted for correct gain at fastest sweep rates. C584-R584
provide thermal compensation.
Basic operation of the Left Output Amplifier stage is the
same as described for the Right Output Amplifier. C586
and C588 set the gain for the fastest sweep rates (C588
affects both Right and Left Output Amplifiers). The output
signal at the collectors of Q578-Q580 connects to the left
deflection plate of the CRT through R585.
The series circuit CR549 and R549 stabilize the output
amplifier during fast retrace intervals. R535 is adjusted to
balance the negative excursions of the right and left sides of
the amplifier when the time base plug-in is used in X10
Magnified mode.
CALIBRATOR AND FRONT PANEL
SWITCHING
The Calibrator and Front Panel Switching circuit pro­
vides output voltage to the front-panel Calibrator pin-jacks
and includes the front-panel switches and controls. Fig. 3-20
shows a detailed block diagram of the Calibrator portion of
this circuit. A schematic of this circuit is shown on
diagram 10 at the rear of this manual.
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