Tektronix 2213 - Page 94

I
NTEGRATED CIRCUITS . An integrated
circuit (IC)
can b e checked with α voltmeter,
test oscilloscope, or by
d irect substitution
.
Α
good understanding of circuit
op eration is
essential to troubleshooting α circuit h aving
an IC . U se
care when checking voltages an d waveforms
aroun
d t he IC so that adjacent leads are n ot
shorte d
together . The grabber tip or an IC
test clip provides α
convenient means of
cli p ping
α
test probe to an IC .
Wh en c h ec k i n g α dio d e, do n ot use an oh
mmeter
range t hat h as α h ig h internal c u rrent .
H
ig
h
c
u rre n
t
can damage t he diode . C
h ec k
s
on d io d es can be
pe r
forme d i n muc h the same man n e r as on tra n sistor
emitte r -to-base j unctio n s . Do not ch ec k tu n nel
diodes
o r bac k dio d es wit h an o h mmeter
; u
se α dynamic
teste r , s u c h as t he TEKTRONIX 576 C
u rve Tracer .
DIODES . Α d io d e can b e checked for either an open or
α s horte d con d ition by measuring the
r
esistance
b etween
terminals with an ohmmeter set to
α r ange having α low
internal source current, such as the R
Χ 1 k Ω range . The
d io d e resistance shoul d b
e very h igh in one d irection and
very low when
the meter lea d
s
are reversed .
Silicon
diod es should have 0 .6 to 0 .8 V across
their
junctions when conducting . H igher rea d ings indicate
that
they
are either reverse biased or d efective, d epending on
polarity .
M
aintenance-2213 Service
RESISTORS . Check resistors
with an ohmmeter . R efer
to the "Replaceable
E lectrical P arts" list for the tolerances
of resistors use d
in
this
instrument . Α resistor normally
d oes not require r eplacement unless
its measured value
varies widely from its specified
value an d tolerance .
I NDUCTORS
. C heck for o p en in d uctors by checking
continuity with an ohmmeter . Shorted or partially shorte d
in d uctors
can usually b e found by checking the waveform
response when h igh-frequency signals
are
passed
through
t he circuit .
CAPACITORS .
Α leaky or s horted capacitor can best
b e d etected by checking r esistance with an ohmmeter set
to one of the h ighest ranges . Do not exceed
the voltage
rating of the capacitor
. The resistance r eading should be
h igh after t
he capacitor is charged to the outp ut voltage
of the
ohmmeter .
An
open capacitor
can
b e detecte d with
α capacitance
meter or b y checking whether t he capacitor
passes ac
signals .
10 . R epair
an d Adjust the Circuit
If any defective p arts are located, follow the r eplace-
ment p rocedures given under "Corrective M
aintenance"
in t his section . After any electrical
component has b een
replace d , the performance
for that p articular circuit should
be
checked, as well as the performance of other closely
related circuits . Since the p ower s upplies affect all circuits,
performance of the entire instrument should be checked if
work has b een d one in any of the p ower supplies
or if the
p ower transformer h as been replaced
. R eadjustment of the
affected circuitry may b
e
necessary
. Refer to the "Per-
formance
Check Procedure" and "A d justment P rocedure"
(Sections
4 and 5) and to Table 5-1 (Ad justment
Interactions) .