Tektronix 576 - Page 62

obtai n e d t hrough t he use of fiber-o p tic rea d out . F iber-o p tic
rea dout involves t he use of plastic fibers of very small
diameter, calle d lig h t tubes, for transferring lig h t from one
p lace to
anot
h er .
T
h
e lig h t tubes are d esigne d so t h at t he
lig h t inci d ent at one en
d of
t he tube
is
transmitte
d t h roug h
t he tube to t he ot h er en d . If t he outp ut en d of t h e t
ube
is
viewed directly, t he outp ut lig h t loo k s li k e α small d
ot
. T h is
transmission of lig h t occurs eve n if t h e lig h t tubes are bent
at slig h t angles . In or d er to form α c h aracter, many lig h t
tubes are arrange d so t h at t h eir out p ut end s, t h e d ots of
lig h t, are in t he configuratio n of t he c h aracter to be
formed . T he i np ut ends are then arrange d so t h at t hey
receive t h eir inci d ent lig h t from t h
e
same lig h t
source
.
In
some cases it may ta ke two
or more
lig h t
sources to form
one ch aracter . Wh en ever t he p
ro p
er lig h t
so u rce (or
so u rces) is illumi n ate d , t he d esire d c h aracter
a p pears . It is
t h e p ur pose of t he rea dout circuitry, t h erefore,
to lig h
t
t
h
e
r ea dout lamp s so t he d eflection factors t h ey i nd icate co r -
res p ond wit h t h
e C R T dis
p
lay d eflection factors deter-
mine d by t h
e
positions
of t he VER TICA L and H O R IZO N -
TA L switc h es, t h e M
OD
E switc h ,
t
h
e DIS PL AY O FF S ET
Selector switc h , t he A MPL IT
U D
E
switc
h
an d the .1X ST EP
Μ UL T button .
T he in pu ts for t he rea dout logic come from
logic lines
w hose logic levels are controlle d by the switc h
es s h own on
t he R eadout Switch ing and I n terconnectio n s sc h ematic, or
by externally p rovi d ed logic levels . T he form
of
t h e i n puts
is α high-low code . N ormally all in p uts are hig h and t he
co d e is determined by switc h ing some of t he logic li n es to
ground . Groun d refe r ence is generally p rovi ded directly as
p
art of t he switc h . H owever, i n t h e case of t he vertical and
horizontal switc h es, gro und is provi ded t hrough saturatio n
transistors
0900 and Q943 res p ectively . If lows are a pp lie d
to pins 7
and
20
of J 363, t h ese transistors are turne d off . In
t
h is case ground reference fo r t he affected logic lines must
then be p rovide d exte rn ally .
T he rea dout logic (see R ea dout L ogic sc h ematic) pri-
marily consists of integrate d circuit decod ers . T h ese de-
coders receive in pu ts from t he incoming logic li n es in terms
of t h e above-mentione d switc h co de . T h is in p ut cod e is
t
h en translate d
i
n
to
α
high-low
lam
p cod
e w h
ic h ap pears on
t h e o u t p ut
logic
lines . E
ac h of t
he
outp ut logic lines is con-
nected to α rea dout lam p (see R ea dout L amps sc h ematics)
a nd eac h lam p illuminates one c h aracter of one part of α
ch aracter . Α low on α rea dout lamp causes t h e lam p to lig h t .
T he intensity of t he rea dout is determined by t h e 0 to 4 .5
volt su pp ly .
T he rea dout logic ci r cuitry also generates α lamp code
w h ic h produ ces α rea dou t of b eta or tra n sco ndu ctance
(g r n)
p er division . T h is β
or
gm
rea dout lamp
co
de is ob-
taine d by d ivi d ing t he
vertical
lamp co d e b y t he ste p s lamp
code .
T h e d ecoders w h ic h control t h e h orizontal d eflection
factor rea dou t are U 951 and U 953 . Inputs to t h ese de-
co
d
ers are controlle d by t he H O R IZO N TA L switc
h ,
t
h
e
DIS PL AY O FF SE T Selecto r switc h or by exte r nally
Circuit
Description-Typ e 576
ap
plie d in
p
uts
to
J 363 . Out
p
uts from t h ese d eco d ers go to
t he horizontal readout lamp s . As an exam p le of h ow α lamp
co d e is generated, assume t h at t h e H O R IZO N TA L switc h is
set to .5 V CO LLE CTO R an d t he DIS PL AY O FF S ET
Selector switc h is set to N O RM (O FF ) . Due to t he closing
of contacts by t he H O R IZO N TA L cam switc h (see t he
R ea dout Switch ing and I n terconnections sc h ematic), lows
are a p p lied to t he in p uts to U951 and U 953 at con nectors
13, Τ , an d S of Ρ 950 (see F ig . 3-13) . T he
ot
h er i np uts
to
t he h orizontal decod ers are h el d h ig h . T h e
out
p
ut lam p
co de resulting from t h is input co d e is lows at lamp in p
ut
connectors F, Ι , J, L, Α , C, D and Ε . T h
e
resulting
PER
HOR IZ DI V rea d out is 500 mV , w h ic h
corres
p
on d s with
t he .5 V CO LLE CTO R p osition
of
t
h
e
H O R IZO N TA L
switc h .
Deco d ers U 956 and U 960
co
n
trol
t
he vertical d eflection
factor rea dout . In p uts to th ese deco d
ers are controlle d by
t he VER TICA L switc h , t h e DIS PL
AY O FF SE T Selector
switc h , t he M OD E switc h and externally a pp
lied in
p uts
to
J 363 . Out p uts from t h ese d ecod ers go to t he vertical read-
ou
t
lam
p
s . T
h
e
h
orizontal and vertical d eco d ers are affecte d
by t h
ese logic in
p
uts, at p in U, p in Υ a nd pin 12 of J 363,
w h ose logic levels may
only be d etermine d externally .
Deco
d
ers
U 965 and U 970 control t h e step am p litu de
rea dout . In p uts to
U 965 and U 970 are controlle d by t he
A MPL IT U D E switc h , t h
e STEP MUL T .1 Χ button and
externally a pp lie d in pu ts
to J 361
.
Outputs from U 965 and
U 970 go to t he ste p s rea dout lam p s .
T he beta or
gm
generator consists of U 974, U 975 and
U 976 . T he i n pu t code receive
d by t h ese decod ers is α com-
bination of logic levels
coming i n p art from t he vertical
lamp cod e, and i n p
art from t he ste p s lam p code . T h e out-
p uts from t h
ese decoders go to t he beta rea dout lam p s .
Q960 and Q974
deco
d
e
t he logic levels app earing at pins 13
and
15 of U 960 and p ins 13 and 15 of U 970 . Q977 and
Q979 provi de α means of lig h ting t h e 1,4
lamp (connector
ΒΙ ) w h enever t he2,5
lam p (con n ector A R ) is off .
P
ower Su p ply
T he Ty pe 576 can be op erate d eit h er from α 115-volt or
α 230-volt line voltage source . T h e
low
voltage p ower sup-
ply (see F ig . 3-14) consists of α single tra n sformer, Τ 701,
w h ic h h as nine second aries . T h is su p ply p rovi d es six regu-
late d voltages : -75 volts, -12 .5 volts,
+5
volts, +12 .5 volts,
+15 volts an d +100 volts . It also p ro d uces α regulate d vari-
able voltage of 0 to 4 .5 volts, one unregulate d voltage of
+50 volts a nd an AC voltage to d rive t he PO WER ON lig h t
and t h e GR ATIC ULE I LLUM lig h ts . T he win d ings p ro-
vi d ing α source of cloc k pu lses for t he ste p generator an d
t
h e CR T heater are among
t
he
nine
second aries of Τ
701 .
All t h e reg u late d p ower s u pp lies are com p letely s h ort
p
roof .
Inp u t Ci r cuit .
Wh
e
n t h
e PO
WER switc h is switc h e d to
ON,
line c u rre n t flows from t h e i np ut, Ρ701 (see Power
S
up p
ly sc h ematic),
t
h roug h
p
ower switc h S W 701, fuse
F 701, T h ermal Cutout ΤΚ 701 and into t he primary win d -
3- 2 1