3-32 Malfunctions Not Indicated by a Fault
4. Check the gate to cathode junction of each SCR of the module as
follows:
Pin 6 to Pin 3
Pin 7 to Pin 2
Pin 8 to Pin 4
Pin 9 to Pin 2
All resistance measurements should be between 15 and 60 ohms. If
outside of this range or if significant deviation between SCR’s is
measured, module replacement may be necessary.
5. With the DMM on the 2 megohm range, check the anode to cathode
junction of each SCR as follows:
Field Pulse/Snubber Circuits (Series B)
The field pulse/snubber circuits, located on the power board, provide
isolation of the gate firing circuit and also provide DV/DT protection for the
SCR modules. A malfunction of these devices will be evident in either an
overcurrent related fault, blown or tripped incoming protection devices or
erratic motor operation. Follow the procedure below:
1. Disconnect and lock out all incoming voltage sources.
2. To gain access to the power board, swing down and remove the PSI/
Switcher board.
3. Remove the gate interconnects between the PCB and field SCR module
(J11, J12, J13, J14).
4. Measure the following resistances with a DMM on the 200 ohm scale.
Measurement Point Measurement
Pin 2 to pin 3 greater than 500k ohms
Pin 2 to pin 4
Pin 1 to Pin 4
Pin 1 to Pin 3
Measurement Point Measurement
TB1-1 (L1) to D7 anode 1 to 2 ohms
TB1-1 (L1) to D7 cathode 100 ohms +/–10%
TB1-2 (L3) to D8 anode 1 to 2 ohms
TB1-2 (L3) to D8 cathode 100 ohms +/–10%
TB1-3 (F+) to D9 anode 1 to 2 ohms
TB1-3 (F+) to D9 cathode 100 ohms +/–10%
TB1-3 (F+) to D10 anode 1 to 2 ohms
TB1-3 (F+) to D10 cathode 100 ohms +/–10%
J6 - 1 to J6 - 19 60 ohms +/–10%
J6 - 1 to J6 - 17 60 ohms +/–10%
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