Tektronix 2235 User Manual

Theo r y of O p eratio n -2235 Service
BEAM F I ND switc h S390 con trols t h e b ase bias voltages

voltage will b e clampe d wh enever t he p ositive p ea ks reac h α
of Q825 and Q829 . Wh en t he BEAM F I ND bu tton is o u t,

level t h at
forward
b iases C
R
851
.
-8 .6 V is supp lied to α base-biasing networ k . Wh en t he
button is pushed i n , t h e -8 .6 V supp ly is removed and t he
voltage at t h e ano de of VR 828 rises to ab o u t -5 .6 V . T h is

T h
e
Ζ -Axis Am p lifier outpu t voltage, w h ic h varies b e-
t u rns off Q829 so t h at t h e amplifier o u t pu t voltage is deter-

tween
+10 V
and
+75 V, is applied to t he Dc R estorer at
mined b y R 835 and t he voltage at t he BEAM F I N D switc h ,

t he anode of C R 853 . T he ac-drive voltage will h old C R 853
as set by ot h er p arts of t h e B eam F ind circuitry . The out p ut

reverse b iased
until
t
h
e voltage
falls
below
t h
e
Ζ -Axis Am p li-
voltage of 0835 will t h en be at α fixed level so t h at t he

fier
out p ut voltage
level . At t h
at
p
oi
n t,
C
R
853 becomes fo
r -
I NT EN SITY controls an d t he Ζ -Drive signal h ave no con trol

ward biased an
d clamps t he j unction of C R 851, CR 853, and
over t he crt intensity . Α b rig h t trace or dot will t hen be

R
854 to
t h
e
Ζ -Axis
outp
u t level . T h us, t h e ac-drive voltage
dis p layed .

is clampe
d
at
two levels to produce α s q uare-wave signal
wit h α positive dc-offset level .
Dc R estorer
Th
e Dc
R
estorer is refere
n
ced to
t h
e -2
kV
crt cat
h
ode
T he Dc R estorer circuit p roduces t he crt con trol-grid b ias

voltage t h ro ugh R 858 an d CR 854 . Initially,
bot
h
C855 a
n
d
a
n
d couples b ot h d o an d ac com p onents of t he Ζ -Axis Am-

C854 will ch arge up to α level determined by t he d iffere n
ce
plifier output to t he crt control gri d . Direct coupling of t he Ζ -

b etween t he Ζ -Axis out p ut voltage and t he crt cat h ode volt-
Axis Amplifier out p ut to t h e crt control grid is not em p loyed

age . Capacitor
C855 c
h
arges
from
t
h
e
Ζ -Axis
outp u t
d ue to t h e h ig h potential d ifferences involve d . R efer to F ig-

t h
ro
u gh R
858, C
R
854, and C
R
855, to t
h
e crt cat
h
ode . Ca
ure 3-5 during t he following discussion .

p acitor C854 charges t h roug h R
858, C
R
854,
R
854, a
n
d
C R 853 to t he crt cat h ode .
Ac drive to t h e Dc R estorer circuit is ob tai ned from pin 16
of Τ 948 . Th e drive voltage h as α peak amplit ude of ab out

During
t
h
e positive transitions of t he ac d rive, from t h e
± 100 V, α fre q uency of ab o u t 20 kH z, and is co u pled i n to

lower clam
p
ed
level
toward
t h
e
h ig h
er clamped level, t h e
t h
e Dc
R
estorer circuit t h ro u gh C853 and R 853 . T h e cat h -

ch arge on C854 increases due to t he rising voltage
.
T h
e
ode of
C
R
851 is biased by t h e voltage applie d from t he

voltage increase across C854 is eq ual to t he amplit ude of
wi p er of Gri d B
ias p otentiometer R 851, and t he ac- d rive

t he positive transitio n . T he n egative transition is cou ple d
+1 φφ V
Z-AXIS
O U T PU T
+10 V
+100V -
0-
AC
D R I VE -1
θθν
-
V O L TAG E FR
O
M
T940, PIN 15
CR 851
C855
C R 853
SΖ

C R
855
- +85 V
-+10 V
R 854
C854
CAT H OD E
8858
V O L TAG E ~_
S UPPL Y
(1--2kV )
C R 854
S Ζ

Ι

( "

) DS856
177
F ig ur e 3- 5 . Simp lifie d d iagra m
Of
t he Dc R esto r e r ci r c u it .
R 86 φ 5

_ j "

Ι

CAT H OD E
6 .2
Μ
C979
CO N TR OL G RI D
DS858
4206-14

Tektronix 2235 Specifications

General

Brand	Tektronix
Model	2235
Category	Test Equipment
Language	English