C ircuit D escription—434
EXT H O R IZ mode of operation. When the T IM E /D IV
switch is set to EXT HO RIZ, the X signal is connected to
the H orizontal A m plifier circu it via the EXT H O RIZ input
connector on the instrum ent rear panel.
The CRT circu it determines the CRT intensity by
summing the signal inputs from the IN TEN S ITY control,
Channel Switch circu it (chopped blanking), Sweep Genera
to r (unblanking), and the Z AX IS input connector. The
CRT c ircu it also contains the controls necessary fo r opera
tion o f the cathode-ray tube. Trace storage is accomplished
by the Storage circuit.
The Power Supply circu it provides all the voltages
necessary fo r operation of this instrum ent. The Calibrator
circuit provides a square-wave outp ut w ith accurate am pli
tude and frequency which can be used to check the calibra
tion of the instrum ent and the compensation of probes.
CIRCU IT OPERATION
General
This section provides a detailed description o f the elec
trical operation and relationship o f the circuits in the 434.
The theory of operation fo r circuits unique to this instru
ment is described in detail in this discussion. Circuits which
are com m only used in the electronics industry are not
described in detail. If more inform ation is desired on these
com m only used circuits, refer to the follow ing textbooks:
Tektro nix C ircuit Concepts Books (order from your
local T ektro nix Field O ffice or representative).
C a th o d e -R a y Tubes, Tektro nix Part No. 062-
0852-01.
Horizontal A m p lifie r Circuits, Te ktronix Part No.
062-1144-00.
Oscilloscope Trigger Circuits, Te ktron ix Part No.
062-1056-00.
Power Supply Circuits, T e ktro nix Part No. 062-
0888-01.
Sw eep G enerator Circuits, Te ktro nix Part No.
062-1098-01.
V ertic a l A m plifie r Circuits, Tektron ix Part No.
062-1145-00.
P h illip C u tle r, "Sem iconductor Circuit Analysis",
M cGraw-Hill, New Y ork, 1964.
Lloyd P. Hunter (Ed.), "H andbook of Semiconductor
Electronics", second edition, M cG raw-Hill, New Y ork,
1962.
Jacob Millm an and H erbert Taub, "Pulse, D igital, and
Switching W aveforms", M cGraw -Hill, New York, 1965.
The follow ing circu it analysis is w ritten around the
detailed block diagrams which are given fo r each major
circuit. These detailed block diagrams give the names of the
individual stages w ithin the major circuits and show how
they are connected together to form the major circuit. The
block diagrams also show the inputs and outputs for each
circu it and the relationship of the front-panel controls to
the individual stages. The c ircu it diagrams from which the
detailed block diagrams are derived are shown in the
Diagrams section.
CHANN EL 1 INPUT AMP AND PREAMP
General
In pu t signals fo r vertical deflection on the CRT can be
connected to the CH 1 connector. The Channel 1 Input
Am p and Preamp circuits provide control o f input coupling,
vertical deflection factor, balance, vertical position, and
vertical gain. A sample of the Channel 1 input signal is also
provided to the Trigger P ickoff and Generator circu it to
provide internal triggering from the Channel 1 signal only.
Fig. 3-2 shows a detailed block diagram of the Channel 1
Input Am p and Preamp circuits. A schematic o f these
circuits is shown on diagram 1 at the rear of the manual.
Input Coupling
Input signals applied to the CH 1 connector can be AC-
coupled, DC-coupled, or internally disconnected. When
Inpu t Coupling switch S8A is in the DC position, the input
signal is coupled dire ctly to the In put A ttenuator circuit. In
the AC position, the in put signal passes through capacitor
C8. This capacitor prevents the DC com ponent o f the signal
from passing to the am plifier. When the GND pushbutton is
pressed in, switch S8B opens the signal path and the input
to the am plifier is connected to ground. This provides a
ground reference w ith o u t the need to disconnect the
applied signal from the CH 1 input connector. Resistor R8
allows C8 to be precharged so the trace remains on screen
when switched to AC coupling w ith a high DC level applied.
Variable capacitor C9 adjusts the basic input tim e constant
fo r a nominal value of one megohm X 24 picofarads.
Input A ttenuator
The effective overall Channel 1 deflection factor of the
434 is determined by the CH 1 V O LT S /D IV switch. In all
positions of the CH 1 V O LT S /D IV switch above 5 m V, the
basic deflection factor of the Vertical Deflection System is
10 m illivo lts per division of CRT deflection. To increase
this basic deflection factor to the values indicated by the
V O LT S /D IV switch, precision attenuators are switched into
the circuit. In the 1, 2, 5, and 10 mV positions, input
attenuation is not used. Instead, the gain of the Preamp
3-3
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