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Page Title:
Isolating Trouble Within Plug-in Unit |
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  TM 11-5805-239-35
Indication
Probable trouble
Item No.
Procedure
Faulty output control
Dc output varies
8
Remove the plug-in unit and
rheostat.
erratically y as
check continuity of resistor
output control is
R3 while slowly rotating
rotated
the control knob. Replace
R3 if resistance does not
vary smoothly.
a dielectric breakdown test. The output of
3-6 Isolating Trouble Within Plug-in Unit
one of the other plug-in units can be used.
a. General.
When
trouble
has
been
local-
Use
the
250-volt
dc
range
of
the
TS352/U
ized to a plug-in unit either through opera-
w h e n making the following test:
tional checks or the use of the troubleshoot-
( 1 ) Connect a test lead to the positive
i n g chart, isolate the defective part by making
side of the voaltge supply, and an-
v o l t a g e or resistance measurements.
other test lead to the negative side.
Before attempting to perform
Caution:
Touch the positive lead to terminal
voltage and resistance measurements, review
4 of plug P1, and the negative lead
t o terminal 3. Keep the leads in con-
imtructions and observe the notes on the ref-
tact
for
approximately
2
seconds;
erence figures; carelessness may cause more
t h i s will charge a good capacitor. Re-
troubles in the equipment and make trouble-
m o v e the test leads from terminals 3
shooting more difficult.
and 4 of plug P1. Remove the test
leads from the power supply.
Warning:
I n power supplies that do not
( 2 ) A f t e r about 1 minute, touch the pos-
have MWO 11-5805-239-35/1 applied, capacitor
itive
lead
of
the
voltmeter
of
the
C1 will be fully charged to the dc output
TS-352/U to terminal 4 of plug P1,
voltage. Use a test lead with an alligator
and the negative lead to terminal 3.
c l i p to discharge C1 as follows: Attach the
If the capacitor is satisfactory, the
alligator clip to the short probe, and clamp
v o l t m e t e r needle will jump to a read-
t h e alligator clip to terminal 4 of plug P1.
ing of approximately one-half of the
Place one hand in your pocket and touch ter
applied
dc
voltage,
and
slowly
re-
minal 3 of P1 with the long probe.
turn
to
zero.
A
weak
kick
of
the
b. T e s t i n g R e s i s t o r R 1 . C h e c k
continuity
needle indicates a faulty capacitor.
between terminals 1 and 2 of plug P1. The
Replace a defective capacitor while
resistance should be 100 ohms (+ 10 percent).
carefully
observing
polarity.
R e p l a c e the resistor if the value is not within
these limits.
e. Testing of Selenium Rectifiers. T o t e s t
c. T e s t i n g
Resistor R2. C h e c k
continuity
the selenium rectifiers on Power Supply PP
1 2 0 9 / F G , proceed as follows:
between terminals 7 and 8 of plug PI. The
resistance should be 5 ohms (+10 percent)
( 1 ) R e m o v e the plug-in unit to be tested
(10
ohms
in
PP-1209B/FG
and
PP-1209C/
from the main chassis assembly.
FG). Replace the resistor if it is not with-
( 2 ) Use the ohmmeter section of Multi-
in these limits.
meter
TS-352/U
to
check
the
for-
ward-reverse resistance ratio of the
d. T e s t i n g F i l t e r C a p a c i t o r C 1 . U n s o l d e r
selenium rectifier. Connect the black
one lead of bleeder resistor R4. Use a low-
t e s t lead of the TS352/U to terminal
resistance range of Multimeter TS-352/U to
5 of plug P1, and the red test lead to
check capacitor C1 for a short circuit. If the
t e r m i n a l 6 of plug P1, Select the re-
capacitor is, not short-circuited, use a source
sistance
range
on
the
TS-352/U
o f dc voltage not exceeding 150 volts to make
3-3
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