IMA 474
DC-400
Page 25
Power Rectifier Bridge Assembly Checking
Procedure
1. Bridge and Device Isolation (See the instruction
manual parts list for the exact location.)
Disconnect the following leads from the bridge, shown
in Diagram 1:
a)
Unplug P3 (G1, G2, G3 and 204) from the Control
PC Board.
b)
Unplug P5 from the Snubber PC Board.
c)
Secondary leads X1, X2, and X3 from the anodes
of the SCR’s and cathodes of the diodes.
d)
Disconnect positive bridge lead from shunt and
positive capacitor bank lead and from lug with
triple 204 leads.
e)
Perform the following steps 2 and 3. If diodes and
SCR’s are not shorted, bridge test is completed. If
any device appears shorted, disconnect the
cathode lead of each diode (4 total) and repeat
Steps 2 and 3.
2. Power Diode Test
a)
Establish the polarity of the ohmmeter leads and
set to X10 scale.
b)
Connect the ohmmeter positive lead to anode and
negative lead to cathode.
c)
Reverse the leads of the ohmmeter from Step b.
d)
A shorted diode will indicate zero or an equally
low resistance in both directions. An open diode
will have an infinite or high resistance in both
directions and a good diode will have a low
resistance in Step b and Step a much higher
resistance in Step c.
3. Power Silicon Controlled Rectifier Test
a)
Connect the ohmmeter (set to m X10 scale) leads
to the anode and cathode.
b)
Reverse the leads of the ohmmeter from Step a.
c)
A shorted SCR will indicate zero or an equally low
resistance in one or both directions.
d)
Establish the polarity of the ohmmeter. Connect
the positive lead to the gate (G1, G2 or G3) and
the negative lead to the cathode (204).
e)
An open gate circuit will have an infinite or high
resistance. A good gate circuit will read a low
resistance, but not zero ohms. If gate circuit reads
zero ohms, check gate harness for shorts
between gate leads and 204 before replacing
SCR.
ELECTRIC SHOCK can kill
•
Have an electrician install and service this equipment..
•
Turn the input power off at the fuse box before working
on equipment.
•
Do not touch electrically hot parts.
WARNING
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