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F-57 F-57
ACTIVE SCR TEST (continued)
FIGURE F.21 - SILICON CONTROLLED RECTIFIER TEST SETUP.
TROUBLESHOOTING & REPAIR
SILICON CONTROLLED
RECTIFIER TEST
(Heat Sink Mounted Units)
To test the SCRs, construct the circuit outlined
in Figure F.21. One 6V lantern battery can be
used. Resistor tolerances are 10%. The volt-
meter scale should be low, approximately 0-5
or 0-10 volts.
BATTERY TEST
Check the battery by shorting leads (A) and (C)
and then close switch SW-1. Replace the bat-
tery if the voltage is less than 4.5 volts.
1. Connect the SCR into the test circuit as
shown: (A) lead to anode, (C) lead to cath-
ode, and (G) lead to the gate. NOTE: the
gate leads are located in plug J1.
2. Close switch SW-1 (switch SW-2 should be
open). The voltmeter should read zero. If
the voltmeter reads higher than zero, the
SCR is shorted.
3. With switch SW-1 closed, close switch SW-
2 for two seconds and release. The volt-
meter should read 3 to 6 volts before and
after switch SW-2 is released. If the volt-
meter does not read, or reads only while
SW-2 is depressed, the SCR or battery is
defective. (Repeat Battery Test Procedure)
4. Open switch SW-1, disconnect the gate
lead (G), and reverse the (A) and (C) leads
on the SCR. Close switch SW-1. The volt-
meter should read zero. If the voltage is
higher than zero, the SCR is shorted.
SQUARE WAVE TIG 355
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To test SCRs construct the circuit outlined above.
Resistor values are plus or minus ten percent. The
voltmeter scale should be low, approximately 0-5 or
0-10 volts DC.