Tektronix 7623, Instruction Manual

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Circuit Description — 7623/R7623 Service
Collector Circuit
The basic circuit is a two-transistor high-speed,
high-voltage operational amplifier with gate-selected input
resistors. The control transistors are Q1438, Q1449, and
Q1452. When these transistors are turned on, their collector
load resistors are added to the amplifier input resistance. In
the FAST mode at QF time, transistor Q1438 is turned on,
allowing Cal adjustment R1439 and R1441 to be added to
the amplifier input resistance. When Z7 is at a ground level,
transistor Q1438 cannot be turned on. Transistor Q1452
works the same way as Q1438, but only at QL time.
Transistor Q1449 is turned on when Z9 is not grounded
and when the OF pulse and the QL pulse are both at a
"high" state in the FAST and VAR PERSIST modes (Z8).
See Fig. 3-43 Basic Collector Circuit.
High Speed Mesh Circuit
The basic circuit is a three-transistor operational
amplifier with gate-selected input resistors. Transistors
Q1412, Q1404, and Q1399 control which resistors are
gated into the amplifier input circuit. When transistor
Q1412 is on, diode CR1399 is reversed biased, and the
LEVEL control and range adjustment network are not
added to the amplifiers input resistance. When transistor
Q1399 is turned on, CR1398 and CR1396 are forward
biased. This removes the LEVEL control and range
adjustment, the pump pulses and the HS Prep adjustment
from the input of the amplifier. When diodes CR1396 and
CR1398 are reversed biased, the pump pulses and the HS
Prep adjustment are added to the input resistance of the
amplifier. In all modes except VAR PERSIST, transistor
Q1347 is on, forward biasing diodes CR1390, CR1348,
CR1353, and CR1341. This allows the FAST adjustment
and control circuits to control the High Speed Mesh. The
inputs to U1302C control the time at which CR1409 or
CR1408 are forward biased. When the U1302C output (pin
8) is high, diode CR1409 is forward biased and CR1408 is
reversed biased. When Z7 is high (at QT) the output of
U1302C will be low. This turns off transistor Q1412,
allowing a transfer pulse to be generated by the high-speed
mesh operational amplifier. It also forward-biases diode
CR1408 so that resistor R1408 is added to the Bi-Stable
operational amplifier. In the FAST mode Transistors
Q1612 and QI 617 reduce the high voltage output so that
the stored information on the High Speed Mesh has the
same vertical and horizontal sensitivity (High Speed Mesh is
closer to the writing gun than the Bi-Stable Mesh).
Transistor Q1601 forms a monostable multivibrator and
transistor Q1606 is an inverter stage. When the NON
STORE button is pressed, capacitor C1600 is allowed to
discharge into the base of transistor Û1601, turning it off.
This turns transistor Q1606 on, removing resistor R1607
from the Bi-Stable Mesh Amplifier input circuit. A high
level pulse is generated at the Bi-Stable Mesh and ground
level at the FGK.
Bi-Stable Mesh Circuitry
The basic circuit is a five-transistor, high-speed,
high-voltage operational amplifier. The Variable Persistence
Fig. 3 43. Basic Collector Circuit.
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