Marconi LORAIN RHM800E50, Manual

Page: 38 / 74

After noting the firing waveform characteris-
tics, place the POWER switch to the OFF
position. Disconnect the oscilloscope probe
leads from the
card under test.
Repeat Steps e) through h) for each remain-
ing firing circuit card. If the waveshape at
any output is missing or abnormal, replace
that respective firing circuit card.
When all tests are completed and any nec-
essary repairs accomplished, perform the
following steps:
Completely disconnect all test
ment leads
the rectifier.
Replace the lower front panel on the
rectifier and secure in place with the
hardware
used.
3)
If the DC output leads were discon-
nected or if the DISCON-
NECT link was removed during
repairs, refer to Test Procedure 6 for
recommended startup procedure. If
the battery was not disconnected
from
output, perform the fol-
lowing step.
Place the POWER switch to the ON position.
the meters and indicators on the rec-
tifier to insure normal operation.
7.15
Use the following general pro-
cedure checking for an open or shorted
condition. The POWER must be placed to the
OFF position. and AC and DC power discon-
nected before proceeding the test. Disconnect the
cathode and gate leads of any to be checked.
The cathode and gate leads may be disconnected at a
terminal board. or the leads themselves may be
from the circuit. If the thydstor has short. lug
type terminals. may be disconnected at
these terminals. If the the
mounted disc- type do not attempt to loosen
the device in order to remove the thydstor
its heat
Disconnect power circuit wiring at the heat
sink, and remove the firing circuit (gate and cathode)
leads at their board. A thydstor tester
be used to for an open or
short. It such a tester is not available, the thyristor can
be checked by the use of an ohmmeter. To
for an
anode-to-cathode short, measure the resistance from
Section 4367
anode-tocathode: a low resistance indicates an
to-cathode short. To check for an open or shorted
ristor gate, measure the resistance of the gate-to-cath-
ode in both directions. A reading of zero ohms in both
directions indicates a shorted thyristor.
A reading of
infinity’ in both directions indites an open thyristor.
Replace the thyristor as required. Refer to Test Proce-
dure 6
rectifier startup following completion of
repairs.
7.16 Test Procedure 7. Use this procedure to check
operation of the load sharing circuit.
This procedure performed with power
applied the AC
ages capable
of producing
fatal electrical
shack
present
at
throughout cabinet.
that accidental not made
with exposed electrical termination while
the is operating.
a) Place the POWER switch to the OFF posi-
tion. Open the meter and control panels and
locate on circuit card
b) Connect the test leads of a DMM to TB3. ter-
minal 2 and terminal 3
Adjust the
DMM so it will indicate a maximum of 8 VDC
when the rectifier is operating.
Place the POWER switch to the ON position.
Since the toad sharing output voltage
with output current, circuit
can be checked at various load
levels as shown in Table
d) Insure that output and load sharing
adjustment controls are properly set in paral-
lel-connected rectifiers equipped with nega-
tive-bus load sharing circuits. Refer to
ADJUSTMENT section of these instructions
for details.
e) If the load sharing voltage remains absent or
irregular after adjustment settings have been
verified, replace circuit A7.
After all tests are completed and before
commencing any necessary repairs, place
the POWER switch to the OFF
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