Tektronix 7704A User Manual

Circuit Description -7704A Service
controls, this stage will maintain optimum focus for all
portions of the display as it switches between readout,
normal or intensifie d d is p lays, slow or fast swee p s, an d
h igh- or low-intensity d isplays .
The F ocus-Gri d voltage re q uire d to maintain α focused
display is fairly constant for low- and me d ium-intensity
d isplays . H owever, for d isplays which require intensity
control settings b eyon d mi d range, the voltage re q uirement
at the
F
ocus Gri d increases linearly with the increase in
intensity drive at the output of the Ζ -Axis Amplifier stage .
CR41121 and zener d io d e VR41121 clip the output level
of the Ζ -Axis Am p lifier stage, so the Auto-Focus Am p lifier
is not activate d for low- or medium-intensity dis p lays .
Quiescently, the ano de of VR41121 rests near zero volts .
The
positive voltage applie d t hrough R41121 sets
the
catho d e
of
VR41121
at about +30
volts . Therefore,
CR41121 is h el d reverse b iase d until its ano d e rises above
about +30 .5 volts . Then the portion of the Ζ -Axis drive
signal that excee d s the 30-volt clip p ing level is cou p le d to
the Auto-Focus Amplifier stage .
Q41133-Q41137-Q41155 are connecte d as an inverting
operational amplifier to amplify the output of the L evel
Clipper and d rive the F ocus-Grid electro d e . Auto-Focus
Gain a d justment R41127 d etermines the amount of
signal
connected
to
the
base of
Q41133
to set
the overall gain of
the Auto-Focus Amplifier . R41131 provides feedback from
the out p ut of this stage to the input . The capacitor shown
next
to
R41131 (
d
iagram 14) represents the gimmick-wire
capacitor wrappe
d aroun d t he resistor bo dy . This gimmick-
wire ca p acitor is positioned to adjust the amount of AC
fee d back giving the b est overall focus of d is p lays with
fast-changing intensity levels .
CRT Control Circuit
The ASTIG adjustment R5002, used in conjunction with
t he F OCUS control to obtain α well- d efined d isplay, varies
the level on the astigmatism gri d . Geometry adjustment
R41171 varies the positive level on the h orizontal d eflec-
tion p late shiel d to control the overall geometry of the
d is p lay .
Two ad justments control the trace alignment by varying
the magnetic fiel d aroun d the CRT .
Υ
-Axis Align adjust-
ment R41173 controls the current through L5007, which
affects the
CRT
b eam after vertical d eflection b ut
before
h orizontal deflection . Therefore, it affects only the vertical
( Υ ) com p onents of the d isplay .
TRACEROTATION
adjustment R5003 controls the
current through
L5003 and
affects both t
he vertical
and
h orizontal rotation of the
beam
.

Tektronix 7704A Specifications

General

Brand	Tektronix
Model	7704A
Category	Test Equipment
Language	English