Maintenance - Tektronix OPTION 10 Service Supplement Manual

464 and 466 Opt ion 1 0
Norm al Trigger Pickoff Am plifier . The t rigger pickoff
am plifier furnishes a sam ple of t he signal from t he Delay
Line Driver t o t he t rigger circuit s . The t rigger circuit s will
use t his signal when one or bot h Trigger SOURCE con
t rol ( s ) is ( are ) set t o NORM .
level . The differing input s act ivat e U50C, which produces a
low - logic level on t he ALT/ CHOP SELECT line t hat t urns
on t he chop generat or . Meanwhile , C1 1 is discharging
t oward a low- logic level via R1 2 . When t he volt age on C1 1
reaches U50C's low t hreshold volt age , U50C will be di s
abled and t he ALT/ CHOP SELECT line will revert t o a
high - logic level . The chop generat or t hen st ops .
The Trigger Vi ew , Add , and Channel 2 circuit s work like
t he Channel 1 circuit .
Transist ors Q321 5 , Q31 1 8 and associat ed part s form t he
Norm al Trigger Pickoff Am plifier . Part of t he out put of
Q3426 , in t he Delay - Line Driver , is t he input t o t he t rigger
am plifier . Pot ent iom et er R3202 , Norm Trig DC Bal , con
t rols t he dc level of Q31 1 8 's collect or volt age so t hat
when t he Trigger LEVEL cont rol is set t o zero , t he sweep
will t rigger at t he zero - volt level of t he displayed signal .
When t he ALT/ CHOP cont rol is set t o CHOP, VERT
MODE swit ch S350 grounds t he ALT/ CHOP SELECT line .
The chop generat or is t hen enabled cont inuously if t wo or
m ore input s are select ed ,
When t he A TIME/ DIV cont rol is set t o X Y, a -8 V
level reaches t he XY SELECT line via CR 48 and R 48. This
level set s t he Vert ical Swit ching Logic circuit t o t he X Y
m ode of operat ion . The -8 V also reaches t he ALT/ CHOP
SELECT line , via R51, t o enable t he chop generat or when
ALT is select ed .
Chopped Blanking Am pli fi er .
When
t he
ALT/ CHOP
but t on is in CHOP, a low - logic level on t he ALT/ CHOP
SELECT line disables U3905D . The high - logic level at
U3905D's out put enables U3905C t o pass t he out put of t he
chop generat or . Capacit or C38 1 3 and R391 6 different iat e
t he Chop pulse t o produce t he fast -rise spikes needed for
blanking pulses . Diode CR1 91 8 lim it s t he posit ive spike and
R38 1 5 lim it s t he base current in Q381 2 . The posit ive- going
part of t he waveform reverse - biases Q381 2 . The negat ive
going spike drives Q38 1 2 rapidly int o conduct ion . The
blanking t im e is det erm ined by t he charging t im e of C381 3
via R391 6 and R381 5 . The posit ive- going out put pulse ,
which is coincident wit h t race swit ching , is connect ed t o
t he Z - Axi s Am plifier via R391 4 .
Scale -Fact or Swit ching. The deflect ion fact or of each
channel is shown by indicat or lam ps behind t ransparent
flanges on t he VOLTS/ DIV knobs . Because t he Channel 1
and Channel 2 circuit work ident ically , only Channel 1 is
described here .
Vert i cal Mode Swi t ch , Di agram 1 7
The Vert ical Mode swit ch produces t he logic necessary
t o put t he Vert ical Swit ching Logic circuit int o t he correct
st at e for t he select ed
vert ical
m ode . The Scale- Fact or
Swit ching circuit select s t he correct scale-fact or lam p t o be
light ed . Diagram 1 7 shows t hese circuit s .
i
When t he oscilloscope is set t o CH 1 or ADD m ode , R 29
is grounded eit her direct ly or , in ADD m ode , t hrough
CR50 . This volt age level on R 29 sat urat es Q51, which pro
vides a posit ive volt age t o lam ps DS52 and DS54 . When J1 0
( t he Channel 1 input connect or ) has a 1 x probe , a coaxial
cable , or no connect ion , t he coding ring ( at t he base of t he
bnc connect or ) is at +1 .2 V as set by R52 and Q52 . The
+1 .2 V t urns on Q52 , whose out put t urns on DS52 , t he 1 X
indicat or lam p . The out put of Q52 also t urns off Q54 ,
which ext inguishes DS54 , t he 1 0X indicat or lam p .
Exclusive- NOR Circuit s . The exclusive- NOR circuit s pro
duce a negat ive pulse on t he ALT/ CHOP SELECT line
when any VERT MODE push but t on is act uat ed ( pressed
in ) . While t he ALT m ode is select ed , t he negat ive pulse
will enable t he chop generat or t o produce clock pulses t o
swit ch t he Vert ical Swit ching Logic circuit t o t he select ed
vert ical m ode for t he next display .
When t he user connect s a 1 0X probe t o J1 0 , a cont act in
t he bnc connect or short s t he shield t o t he coding ring at
t he base of t he connect or . This connect ion grounds t he
base of Q52 , t urning off Q52 and 1 X indicat or DS52 . The
collect or volt age of Q52 t hen t urns on Q54 , which light s
1 0X indicat or DS54 .
When t he CH 1 VERT MODE but t on is depressed , t he
condit ion of exclusive- NOR circuit U50C is as follows .
MAINTENANCE
1 . The pin 8
and 9
input s are at high - logic levels .
Capacit or
C1 1 has charged
t o a high - logic level
t hrough R 1 2 .
The m aint enance inst ruct ions in Sect ion 4 of t he 464
or 466 Service m anual are applicable t o t he Opt ion 1 0
inst rum ent .
2. The out put , pin 1 0 , is at a high - logic level .
Obt ai ni ng Replacem ent Part s
When t he CH 1 but t on is released , U50C's pin 9 input
im m ediat ely receives a low -logic level , but because C1 1
is charged t o a posit ive volt age , pin 8 st ays at a high - logic
St andard Part s . Most elect rical and m echanical part s for
Opt i on 1 0 can be obt ained t hrough your local Tekt roni x
Field Offi ce or represent at ive. However , you should be able
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