Malfunctions Not Indicated by a Fault 3-29
5. The thermal switch is mounted in the middle of the main heat sink. In a
normal, cool ambient, measure the resistance between TB1–17 and 18
on the Feedback board. The resistance should be less than 2 ohms.
Series B
1-30 HP, 230V AC
2-60 HP, 460V AC
Armature SCR’s Series B
The 1395, 1-30 HP 230 VAC/ 2 - 60 HP 460VAC armature supply consists
of six dual pack SCR modules mounted on the main heat sink. A
malfunction of any of these devices will show itself in either an overcurrent
related fault, blown or tripped incoming protection devices, or erratic motor
operation. The following procedure can be used if an armature bridge
component malfunction is suspected.
1. Disconnect and lock–out ALL incoming voltage sources. Verify that the
three–phase high voltage is removed from the incoming protection
devices, either F1 – F3. Also verify that the 115V logic supply and
contactor power is removed from TB2–1, 2, 3. To gain access to the
Power Board, swing down and remove PSI/Switcher Board.
2. Check the Anode to Cathode junction of each SCR module. With a
DMM on the 1 Megohm scale, measure the resistance across the SCR
modules as follows (refer to
Figure 3.14).
Measure from . . . To . . .
PM1
A1 (bottom of DC contactor)
A2 (bottom of DC contactor)
PM2
L1 (bottom of F1)
L1 (bottom of F1)
PM3
A1 (bottom of DC contactor)
A2 (bottom of DC contactor)
PM4
L2 (bottom of F2)
L2 (bottom of F2)
PM5
A1 (bottom of DC contactor)
A2 (bottom of DC contactor)
PM6
L3 (bottom of F3)
L3 (bottom of F3)
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