Tektronix 2213 - Page 53

Wh
en
t h e ac-drive voltage
starts its positive tra n sition
from t he lower clam p ed level
toward t he h ig he r clamped
level, t he ch a r ge on C864
i nc r eases due to t he risi ng
voltage . T he i nc r ease in c h arge
acq uired by C864 is
proportional to t he amplitu de of
t h e p ositive transitio
n .
Wh en t he ac-drive voltage starts
its negative tr ansitio n
from
t h e upper clam p ed
level to t he lowe r clampe d
level, t h e
negative transitio n is cou p le d
t h ro ugh C864 to
r
everse
b ias
C R 867and to forward
bias C R 868 . T he i nc r eased c h arge of
C864 is t hen transferre
d to C865 as C864 disc
harges
towar d t he Ζ -Axis ou tput
level . T he amou n t of c h arge
t h at is
t r ansferred is pro p
ortional to t he setti ng of
t h e A U TO
I N T EN SITY
control, since t h at control
sets t he lowe r
clam p ing level of
t h e ac-d r ive voltage .
T he a d d ed c h arge on C865 also
determines t he co n trol-
grid bias voltage . If mo r e charge is added to
t h
e c
h arge
alrea dy p resent on C865, t
h
e
control grid b ecomes more
3- 26
F ig ur e 3-8 .
Simplifie dd iag r am of th e DC r estorer
ci r cuit .
Theory of
O pe r atio n -2213 Service
negative, and less crt writing- b eam current will flow .
Co n versely, if less c ha r ge is adde d , t he cont r ol-g r i d voltage
level will b e closer to t h e cat h o d e-voltage level, an d more crt
writi n g-beam current flows .
D ur i n g periods t h at C865 is ch argi n g, t h e crt
control-gri d
voltage is h eld co n sta n t b y t h e long time-consta
n t disc h arge
pat h of C865 t hr oug h 8868 .
F ast- r ise an d fast-fall tra n sitio n s of t he Ζ -Axis ou t p ut
signal are coupled to t h e crt cont r ol grid t h ro u g h C865 .
T h
e
fast tr ansitions start t he crt writing- b eam c u rrent toward
t h
e
new intensity level . T he DC R estore r ou t pu t
level t h
en
follows t he Ζ -Axis o u tput-voltage level to set t
h
e
new bias
voltage for t h e crt control grid .
Neon lamps DS867 an d
DS868 p rotect t he crt from
excessive grid-to-cat
h
ode
voltage if t h e p ote n tial on eit h e r
t he con trol grid or t h e cat
h
ode
is lost for any reason .
+1 Φ 0 V
-AX I S
O U T PU T
AC D RI VE
V OL TAG E
FR OM
T940, PIN
16
+15 Φ V-
θ
-
η +1 Φ V
ΤΟ +75 V
L-+10
V
CAT H OD E
8867
V O L TAG E
S UPPL Y
( ; ~ -2 kV )
CO N T R OL G R I
D
C R 867 5 Ζ

Ι

(-- )
DS868
DS867
3828-28
ADD NO V
1982