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FUSE 2
FUSE 1
FUSE 2
FUSE 1
TB4-3
J2 C
TB4-1
CRS
-
CR7
TB4-3
1J2<
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r---r--i
I
---ct--
[ ) t - - - - -
~:kl----
------
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SCR2
SCRl
------<>
TB3-1
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TB3-3
FIGURE 116. CONVERTER-INVERTER TEST POINTS
Types of Failures
F oliowing are the four generai cla::s::sificatiu111:; of
failures on the converter-inverter.
1.
Inverter blows fuses on start.
2. Inverter blows fuses when load is applied.
3. Inverter blows fuses after running for a
short time.
4. Input circuit breaker trips on start.
Inverter Fuses Blow on Start:
If
the SCR gate sig-
nals are normal, use the following procedure to
locate the fault.
1.
Remove the converter-inverter cover
(Figure 115).
2. Replace the blown inverter fuses.
3. With all power removed from the machine,
use an ohmmeter to test the components attached to
the terminal board terminals in Figure 116 and locate
the faulty component. Remove the inverter chassis
if necessary.
Inverter Fuses Blow When Load is Applied:
If
the
SCR gate signal"' are normal, scope the SCR gate
signals for noise while the unit is running with no
load. Also, the turn-off time of a newly replaced
SCR may not meet the specification.
Inverter Fuses Blow After Running a Short Time:
If
the SCR gate signals are normal, watch for a change
with temperature rise that comes with the application
of a load. Check the inverter components per Fig-
ure 116. Remove the inverter chassis if necessary.
t__ ____
-r__j
I
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SCR3
SCR4
JS-4
· Inverter Circuit Breaker Trips on Start: This symp-
tom indicates either a short-circuited load or a
faulty inverter component.
Remove the normal load
to prove whether the load is shorted or not before
testing for faulty components with an ohmmeter
(Figure 116).
Converter-Inverter Fuse Replacement
The converter-inverter fuses may be reached for
replacement by removing main power plug Pl from
its socket on the back of the PDU and opening the
access door.
Converter- Inverter Troubleshooting
Converter-inverter troubles can be worked on with-
out any load. For instance, remove P2-P6 and no
de voltages will be generated.
Voltage Regulator Test Points
Figure 117 shows the meter test points and the ripple
test points of all the voltage regulators in the 2050
Processing Unit.
The ripple, including noise and
voltage variation, should not exceed ±4%.
Changing Voltage Regulators
Remember that with a normal power-off, the 28 volt
bias voltage is still present on all voltage regulators.
To remove this bias voltage in order to change a
regulator, manually trip circuit breaker 9.
Power System Service CheckJ
(3/71)
123
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