Marconi LORAIN RHM800E50 Manual page 38

After noting the firing waveform characteris-
tics, place the POWER switch to the OFF
position. Disconnect the oscilloscope probe
leads from the circufi 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 eguip-
ment leads horn the rectifier.
Replace the lower front panel on the
rectifier and secure it in place with the
hardware originalfy used.
If the DC output leads were discon-
3)
nected or if the BATTERY DISCON-
NECT link was removed during
repairs, refer to Test Procedure 6 for
recommended startup procedure. If
the battery was not disconnected
from rectifier output, perform the fol-
lowing step.
Place the POWER switch to the ON position.
tifier to insure normal operation.
7.15 m Use the following general pro-
cedure when checking thydstors for an open or shorted
condition. The POWER switch must be placed to the
OFF position. and AC and DC power sooumes discon-
nected before proceeding wkh the test. Disconnect the
cathode and gate leads of any thyrtstor to be checked.
The cathode and gate leads may be disconnected at a
terminal board. or the leads themselves may be diion-
type terminals. circuit wiring may be disconnected at
these terminals. If the rectaier utilffes the ctamp
mounted disc- type thyristors. do not attempt to loosen
the cfampfng device in order to remove the thydstor from
its heat sink. Disconnect power circuit wiring at the heat
sink, and remove the firing circuit (gate and cathode)
leads at their temrinal board. A thydstor tester should
be used to check for an anode-to-x&ode open or
short. It such a tester is not available, the thyristor can
be checked by the use of an ohmmeter. To chack for an
anode-to-cathode short, measure the resistance from
anode-tocathode: a low resistance indicates an anode-
to-cathode short. To check for an open or shorted thy-
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.
infinity' in both directions indites an open thyristor.
Replace the thyristor as required. Refer to Test Proce-
dure 6 for rectifier startup following completion of
repairs.
7.16 Test Procedure 7. Use this procedure to check
operation of the load sharing circuit.
This procedure is performed with power
applied to the rectifier: Eazardous AC wlt-
of producing severe. pernaps
ages capable
fatal electrical
shack
throughout
that accidental contact is not made
with my exposed electrical termination while
the n?e@fm is operating.
a) Place the POWER switch to the OFF posi-
tion. Open the meter and control panels and
locate TB3 on circuit card A9.
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 cinuk output voltage
levels as shown in Table 7-l.
d) Insure that output vottage and load sharing
adjustment controls are properly set in paral-
lel-connected rectifiers equipped with nega-
tive-bus load sharing circuits.
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 card A7.
commencing any necessary repairs, place
the POWER switch to the OFF posttiin.
Section 4367
A reading of
present
at
cabinet.
Refer to
Page 35