Tektronix 434, Instruction Manual

Page: 38 / 222

S E C T IO N 3
C IR C U IT D E S C R IP T IO N
434
Change in fo rm a tio n , i f any, a ffe c tin g this section w ill be fo u n d a t the rear o f the manual.
In tro d u c tio n
T his section o f the manual contains a description o f the
c irc u itry used in the 434 Oscilloscope. The description
begins w ith a discussion o f the in stru m e n t using the basic
block diagram shown in Fig. 3-1. Then, each c irc u it is
described in d e ta il, using a detailed b lo ck diagram to show
the interconnections between the stages in each m ajor
c irc u it and the relationship o f the front-panel c o n tro ls to
the individual stages.
A com plete b lo ck diagram is located in the Diagrams
section at the rear o f this m anual. This b lo ck diagram shows
the overall relationship between all o f the c ircu its. C om ­
plete schematics o f each c irc u it are also given in the
Diagrams section. Refer to these diagrams th ro u g h o u t the
fo llo w in g c irc u it description fo r electrical values and
relationship.
BLO C K D IA G R A M
General
The fo llo w in g discussion is provided to aid in un d e r­
standing the overall concept o f the 4 3 4 before the in d i­
vidual circ u its are discussed in d e ta il. A basic block diagram
o f the 434 is shown in Fig. 3-1. O n ly the basic in te r­
connections between the in d ivid u a l blocks are shown on
th is diagram . Each b lo ck represents a m ajor c irc u it w ith in
th is in stru m e n t. The num ber on each b lo ck refers to the
com plete c irc u it diagram w h ich is located at the rear o f this
manual.
Signals to be displayed on the C R T are applied to the
CH 1 a n d /o r CH 2 in p u t connectors. The in p u t signals are
then a m p lifie d by the Channel 1 In p u t A m p and Preamp
a n d /o r th e Channel 2 In p u t A m p and Preamp c ircu its. Each
vertical c irc u it includes separate vertical d e fle ctio n fa c to r,
p o sitio n, in p u t co u p lin g , gain, variable a tte n u a tio n , and
balance controls. A sample o f the Channel 1 signal is
supplied to the Trigger P ic k o ff c irc u it. The Channel 2
Preamp c irc u it contains an in ve rt feature to in v e rt the
Channel 2 signal as displayed on the C RT. The o u tp u t o f
b o th V e rtica l Preamp c irc u its is connected to the Channel
S w itch c irc u it. T his c irc u it selects the channel(s) to be
displayed. A n o u tp u t signal fro m this c irc u it is connected
to the 2 A x is A m p lifie r c irc u it to bla n k o u t the between-
channel sw itching transients w hen in the chopped mode o f
ope ra tio n . A sample o f the signal present in the Channel
S w itch c irc u it is supplied to the Trigger P ic k o ff c irc u it.
The o u tp u t o f the Channel S w itch c irc u it is connected
to the V e rtica l O u tp u t A m p lifie r through the Delay Line.
The V e rtica l O u tp u t A m p lifie r c irc u it provides the final
a m p lific a tio n fo r the signal before i t is connected to the
vertical d e fle c tio n plates o f the C RT. This c irc u it includes
the B EA M F IN D E R sw itch w h ich compresses the vertical
and h o riz o n ta l d e fle ctio n w ith in the view ing area to aid in
locating an off-screen display.
The Trigger P ic k o ff and Generator c irc u it selects a
trigger signal (determ ined by the T R IG G E R SOURCE
sw itch) and produces an o u tp u t pulse w hich in itia te s the
sweep signal produced by the Sweep Generator c irc u it. The
internal trigger signal is selected fro m the Channel 1 c irc u it
o r the Channel S w itch c irc u it. A sample o f the line voltage
applied to the in stru m e n t or an external signal applied to
the E X T T R IG in p u t connector can also be used to gener­
ate a sweep-starting pulse. The trigger c irc u it contains level,
slope, coupling, and source controls.
The Sweep Generator c irc u it produces a linear saw tooth
o u tp u t signal when in itia te d by the Trigger Generator
c irc u it. The slope o f the saw tooth produced by the Sweep
G enerator c irc u it is co n tro lle d by the T IM E /D IV sw itch.
The operating mode o f the Sweep Generator c irc u it is
co n tro lle d by the sweep M O DE sw itch. In the A U T O mode
o f o p e ra tio n , the absence o f an adequate trigger signal
causes the sweep to free ru n . In the N ORM mode, a h o ri­
zontal sweep is presented o n ly w hen c o rre c tly triggered by
an adequate trigger signal. The S IN G L E SWEEP mode o f
o peration allow s one (and o n ly one) sweep to be in itia te d
a fte r the c irc u it is reset w ith the RESET b u tto n . The Sweep
Generator also produces an u n b lan kin g gate signal to
u n b lan k the CRT so the display can be presented. T his gate
signal is c o in c id e n t w ith the saw tooth produced b y the
Sweep Generator c irc u it. A d d itio n a lly , the Sweep Genera­
to r c irc u it produces an alternate trace sync pulse w hich is
connected to the Channel Sw itch c irc u it. This pulse
switches the display between channels at the end o f each
sweep when in the A L T mode o f operation.
The o u tp u t o f the Sweep Generator c irc u it is a m p lifie d
b y the H o rizo n ta l A m p lifie r c irc u it to produce h orizontal
d e fle c tio n fo r the CRT in all positions o f the T IM E /D IV
sw itch except E XT H O R IZ . T his c irc u it contains a six-
p o sitio n m agnifier sw itch to increase the sweep rate up to a
m axim u m o f 50 times. O ther h o rizo n ta l d e fle c tio n signals
can be connected to the H o rizo n ta l A m p lifie r by using the
®
3-1