Tektronix 2213 - Page 49

T h eory of Operatio
n -2213 Service
Q703 is one- h alf of α diffe r e n tial am
p lifie r compose d of
Q703 a nd Q706 . T h e base of 0706 is refe
r enced to gro u nd
t h roug hR 706 . Transisto r Q708am
p lifies t he o u tput sig n al
from t h e collector of Q706 and ap plies
it
to
t h e drai n of
FE T 0714 . Α fee db ack network com p osed of
R 709, R 708,
and C708 is con nected b etwee
n
t
h
e
collector of Q708 an d
t he b ase of Q703 . T h e feed bac
k n etwo rk sets t h e overall
gain of t h e Χ Υ Am p lifie r , wit
h Χ -Gai np otentiometer R 709
ad j usta b le to obtain t
h
e exact
gain r eq ui r ed .
T he Χ -Axis signal p asses t
h
roug
h FE T Q714 an d is
applie d to the base of Q731
in t h e H orizontal P ream p lifier .
H orizontal positio n ing c
u rre n t on t he base of 0730 is
a dd ed to t h e Χ -Axis
sig n al by t he action of t he d
ifferential
amplifier . T
hen t he sum of t h ese two cu rr e n ts is
amplifie d
b y Q736 an d
applied to t he in pu t of t he H
orizo n tal Out p ut
Amplifier .
H orizontal
Out p ut Am p lifier
T
h
e
H orizontal Output Am p lifier
converts
t
he single-
en de d output
of t he P reamplifier into t he
d ifferential
ou t p ut re q
uire d to drive t he crt h orizo n tal
deflection
prates . T
h
e
ou tput stage consists of an input
parap h ase
amplifier and an
outpu t com p lementary amplifier
.
H orizo n
tal sig n al voltage from Q736 is a p
plied to t h e
b ase of Q763 .
T he base of t he ot h e r transistor (Q753)
in
t he p ara p
h ase am p lifier, is biase d t h ro ug
h
α
voltage divi d er
com
p osed of R 758, R757, an d R
756
.
H orizo n tal centeri ng
between t he Χ 1 and Χ 10 M
agnified sweep s is accomplis h ed
by ad j usting M ag R egistration
potentiometer R758 .
Gain of t he p arap
h ase amplifier is determine d by com-
p o n en ts conn ected
between t h e emitter lea d s of Q763 and
Q753 . T he exact gain is a
d j uste d by H oriz Gain p otenti-
ometer R 752 .
Transistor Q747 s upp
lies t h e emitter curre n t to
bot h
Q763 a nd Q753 . T
h e horizo n tal p ortion of t h e B eam
F in d
circuitry affects
t h e available c u rrent to Q747 . N
ormally,
-8 .6 V is a pp lie d to t
h
e
emitter of Q747 from t he BEAM
F I ND switc h via C R 745
and R746 . Wh en t he BEAM
F
I
N
D
push b u tton is p
ressed in, t he direct -8 .6 V
is remove d .
In t h is
con d ition, -8 .6 V is supplie
d via R 745 w h ic h
re d uces
t he current available, t
h ereby re d ucing t he outp ut
voltage swing ca p a b ility of 0763
and Q753 . Dio d es CR 772,
CR
782, CR 783, a nd C R
773 preve n t t he pa r a ph ase
am p lifier from over d
riving t he output amplifie r stage w
hen
the Χ 10 M ag n
ificatio n feat u re is in use .
F inal am
p lification of t h e h orizontal
d eflectio n signal
is p rovi ded by t
he com p lementary- p air out
p ut stage . B ot h
sides of t h e
differential output amplifier
are i d entical in
function, so only
one si d e is d iscusse d
in d etail .
3-
22
Transistors Q780 and Q785 form α
casco d e fee db ac k
amplifier
. Gain of the stage is set by feed
b
ac
k resistor
R 785, an
d h ig h -s peed compe n sation is p rovi
d
ed
b y
C783
and a dju
stable capacitor C784 . F or d o a
n
d low-frequency
components
of t he horizontal d eflectio n
signal,
Q789
acts
as α
current source for 0785 . H ig h -freque n cy com p
one n ts
of t
h e sig n al are co up le d t h roug h C789 to t h
e emitter of
0789 to spee
d up t he outpu t respo n se time .
E mitter voltage for b ot h Q780 an d
Q770 is supp lie d b y
α circuit
com p ose d of Q765 and associate d com p
onents .
T
h e emitter voltage is maintaine d at α
level
t
h at p rovides
p roper b iasing for Q763 an d Q753 .
Diod es C R 770 and
C
R 780 set up an emitter- b ias d
ifference between Q780 an d
Q770, causing t he b ase
voltage of b ot h transistors to be
eq ual .
P O
WER
S
UPPL Y
Th e P owe r Su pp ly circ u itry co
n verts t he ac-so u rce
voltage into t he vario us voltages
n ee d e d for i n st ru ment
operation . It consists of t he P ower
I npu t, Pr eregulato r , and
I n verter ci r c u its (w h ic h d rive t
h
e p
rimary of t he powe r
transforme r ) and ot he r Seco nd ary
circuits (w h ic h produce
t he necessary supp
ly voltages fo r t h e i n st ru me n t) .
T h is i n str u
ment h as eit h er t h e C u rre n t L imit boar d ( Α 19)
or t he Pr eregulator
b oa r d ( Α 18) installed as part of t h e
p ower supp
ly . R efer to t h e appro p riate ci r cuit d escri p tio n for
your
p artic u la r inst ru ment config u ration .
ΝΟΤΕ
I n
st
r uments wit hα S N Β 020100 or ab ove co n tai
n th
e
P
reregulator boar d . Some i n str u me n ts below t
h
is
serial nu mber we r ebu ilt co n
taining t h
e
Pr eregulato r
board . To deter mi ne if you
r
s is o
n
e
of t h ese, loo k to
see if t h ere is an Option 48 stic k er attac
h
ed to
t he
rear of t he inst ru me
n t . If t h
e
r e is n ot an O p tio n 48
stic ke r attac hed and
t h
e
serial n um b er is below
Β 020100, your instrume
n t contains t he Cur r e n t L imit
boa r d .
C urr e n t L imit B oa rd Co n
figuratio n
T h e P ower switc
h (S901) connects t he line voltage to t h e
i n st r ument t h roug h
li n
e
fuse F 901 an d tr an sient su pp ressor
VR 901 . Supp resso
r VR 901 protects t he instrument from
large voltage
transients . H ig h -fre qu e ncy line noise is attenu-
ated by C901 .
T he P rereg u lator circ u it
converts t h e ac-power-sou r ce in-
p ut voltage to α regulated do
voltage . Α triac is used as α
switc h to cond u ct curre
n t duri ng α controlled p e r iod of t h e
input-line-voltage cycle so t h at e
n
e
r gy to b e use db y t h e
I n verter circuit is stored
i n cap acitor C937 .
REV N O V 1982