Tektronix 454A - Page 104

M ai nt enance- 454zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ‘ / R
454A
t h e
ci r cui t i s
wor
k i ng cor r ect l y up t o t h at poi nt . F or ex-

T h e p i n connect or s use d i n t h i s i nst r ument
al so pr ovi de
am p l e, cor r ect sawt oot h o u t p u t at t h e ‘ S WEEP
connect or

± conveni ent means
of ci r cui t i sol at i on
.
F or exam p l e, i f t h e
i ndi cat es t h at t h e ‘ Tr i gger Gener at or and ‘ Swee p Gener -

p ower su pp l y i s s h or t e d , t h e d ef ect i ve ci r c u i t can
be
i so
at or ci r cui t s ar e
o p er at i ng cor r ect l y .

l at e d by d i sconnect i ng t h e p i n connect or s at t h e b oar d s
unt i l t h
e
s h or t i ng con d
i t i on i s r emoved .
I ncor r ect o p er at i on of al l ci r c u i t s of t en i ndi cat es t r oubl e
i n t he power su p p l y . C h ec k f i r st f or cor r ect vol t age of t h e

7 . C h ec k V ol t ages a n d W avµ f or ms . Of t en t h e d ef ect i ve
i n d i vi d
ual su pp l i es . H owever , ± d ef ect i ve com p onent el se-

com
p
onent
can
b
e l ocat e d
by
c h ec
k
i ng f or t h e cor r ect vol t -
w h er e i n t h e i nst r
ument can a p p ear as ± power - sup p l y

age or wavef or m i n t h e ci r cui t . Ty p i cal vol t ages an d wave
t r oubl e an d may al so af f ect t h e o p er at i on of ot h
er
ci r cui t s
.

f or ms ar e gi ven on t h e d i agr ams .
‘ s h or t ci r cui t i n any r egul at e d su pp l y causes t h e out p
ut
l evel of al l s u pp l i es i n t h i s i nst r ument t o d r o p t o zer o u nt i l
t h e s h or t i s r emove d . ‘ s h or t i n t h e +150- vol t u nr eg u l at e d

NOTE
sup p
l y
causes t h e out p u t of t h e r eg u l at e d su pp l i es t o d r o p
and al so o p ens t h e 150 V f u se . I f t h e out
p
u t l evel of
al l
t h e

V ol t ages and wavef or ms gi ven
on
t h e di agr ams ar e
s up p l i es i s i ncor r ect , c h ec k t h at
t
h e L i ne V ol t age Sel ect or

not absol ut e and may var y sl i g h t l y bet ween i nst r u-
Assembl y i s set f or t h e cor r ect l i ne vol t age an d r eg u l at i ng

ment s . To obt ai n oper at i on condi t i ons si mi l ar t o
r ange . Tabl e 4- 3 l i st s t h e t ol er ances of t h e p ower s u pp l i es i n

t h ose used t o t a k e t h ese r eadi ngs, see t h e f i r st di a-
t h i s i nst r ument . I f ± p ower - su pp l y vol t age i s wi t h i n t h e

gr am page .
l i st e
d
t ol er ance, t
h
e sup
pl y ca n be ass umed t o be wor k i ng
cor r ect l y . I f out si d e t h e t ol er ance, t h e s u p p l y may b e mi s-
a d j ust e d or op er at i ng i ncor r ect l y . U se t h e p r oce d ur e gi ven

8 .
C h
ec
k I n d i vi d ual Com p onent s . T h e f ol l owi ng gr o-
i n t h e Cal i b r at i on sect i on t o a d j u st t h e p ower s u pp l i es .

ce d ur es d escr i be met h o d s of c h ec k i ng i n d i vi d u al com p o-
nent s i n t h e 454 ‘ . Com p onent s w h i c h ar e sol d er e d i n pl ace
ar e best c h ec k ed by d i sconnect i ng one end . T h i s i sol at es t h e
TA BLE 4- 3

meas u r ement f r om t h e ef f ect s of s u
r r oun
d
i ng ci r cui t r y .
P ower Sup p l y Tol er ance
‘ . T R A N SI STO R S . T h e best c h ec k of t r ansi st or o p er -
Typi cal
R
i pp
l e

at i on i s act u al p er f or mance u n d er o p er at i ng con
d
i t i ons .
I f
±
P ower Su pp l y

Tol er ance

( maxi mum)

t r ansi st or i s sus p ect e d of
bei ng
d
ef ect i ve, i t can b est b e
- 1960 vol t

±58 . 5 vol t s

c h ec k e d by subst i t ut i ng ±
new com p onent or one w h i c h h as
- 12 vol t

±0 . 12 vol t

2 mi l l i vol t s

been
c h ec k
e
d p r evi ousl y . H owever , be sur e t h at ci r c u i t con-
+12 vol t

12 . 1 vol t s, ±0 . 21 vol t '

2 mi l l i vol t s

di t i ons ar e suc h t h at ± r e p l acement t r ansi st or wi l l not al so
+75
vol t

+0 . 75 vol t

2 mi l l i vol t

be
d amaged . I f su b st i t ut e t r ansi st or s ar e not avai l abl e,
u se ±
d ynami c t est er ( suc h as Te k t r oni x Type 576) . St at i c- t y p
e
¹ Adj u st e d f or cor r ect out p u t f r om t he Cal i b r at or ci r cui t ; see Ca
¹ i -

at i on u n
d
er
si m u l at e d o p er at i ng con d i t i ons .
b r at i o n P r oced u r e .
F i g . 4- 3 pr ovi d es ± gui d e t o ai d i n l ocat i ng ± d ef ect i ve
ci r c u i t . T h i s c h ar t may not i ncl u d e c h ec k s f or al l p ossi bl e
d ef ect s ; use st e p s 6- 8 i n s u c h cases . St ar t f r om t h e t o p of
t h e c h ar t an d per f or m t h e gi ven c h ec k s on t h e l ef t si d e of
t he p age unt i l ± st ep i s f ound
w h
i c h does not p r o d u ce i n d i -
cat e d r es u l t s . Fu r t h er c h ec k s an d / or t h
e
ci r cui t i n w h i c h t h
e
t r ou b l e i s pr o b a b l y l ocat e d ar e l i st e d t o t h e r i g h t of t h i s
st e p .
Af t er t h e d ef ect i ve ci r cui t h as b een l ocat e d , pr ocee d
wi t h st eps 6 t h r oug h 8 t o l ocat e t h e def ect i ve com p o-
nent ( s) .
4- 6
t est er s ar e not r ecommen d e d , si nce t h ey d o not c h ec
k
o p
er -
P O WER swi t ch must be t ur ned of f bef or e r emovi ng
or r epl aci ng t r ansi st or s .
’ . DI OD E S . ‘
d
i o
d
e can
b
e
c h ec k
e
d f or
an
o p en or
s h or t ed condi t i on b y measur i ng t h e r esi st ance b et ween t er -
mi nal s . W i t h an o h mmet er scal e h avi ng an i nt er nal so u r ce of
b et ween 800 mi l l i vol t s an d 3 vol t s, t h e r esi st ance s h oul d b e
ver y h i g h i n one di r ect i on an d ver y l ow
w
h en t h e l ea
d
s ar e
r ever se d .
CA U
TI O N
6 .

C
h
ec
k Ci r cui t B oar d

I nt er connect i ons . Af t er t h e

Do not use an o h mmet er scal e t h at h as ± h i g
h
i nt er nal
t r oubl e h as
b een i sol at ed t o ± par t i cul ar ci r cui t , c h ec k t h e

cur r ent . H i g h cur r ent s may damage t
h e di ode . Do not
pi n connect or s
on
t h e ci r cui t boar d f or cor r ect connect i on .

measur e t h e
t unnel di odes wi t h an o h mmet er , use ±
F i gs . 8- 1 t h r oug h 8- 16 s h ow t h e cor r ect connect i ons f or

dynami c t est e r ( suc h as
± Te k t r oni x Type 576
eac h boar d .

Tr ansi st or - Cur ve
Tr acer ) .