32
IM620-1
If the resistance is less than 20 ohms, it is likely that the Output Board, the ICM Terminal Board,
or an external (field supplied) load is excessively loading the 5 Vdc power supply. Isolate the
problem by measuring resistance on each of these devices with the wires off. The resistance
across the power input terminals on the Output Board (+ and –) should not be less than 3000
ohms. When the field wiring and the OB are disconnected, the resistance across the power input
terminals on the ICM Terminal Board (H7-1 and H7-2) should be infinite. If the component
resistances are proper, check the resistance of the field supplied loads (if any) and check the
wiring and connections throughout the 5 Vdc power supply circuit.
10. Disconnect the connector plugs from the modem and the power plug from all AOX-4 boards (as
applicable). With circuit breaker CB1 open, measure the resistance between field terminals “DC-
GRD” and “13 Vdc.” It should be infinite.
a.
If the resistance is infinite, go to step 12.
b.
If the resistance is not infinite, a short exists somewhere in the 13 Vdc power supply.
11. Reconnect the Aux/Out connector plug to the MCB. If there’s a modem, reconnect its AMP plug
to port A. With circuit breaker CB1 open, measure the resistance between field terminals “DC-
GRD” and “13 Vdc.” It should steadily rise to a value greater than 5000 ohms (within
approximately 30 seconds).
a.
If the resistance rises above 5000 ohms, go to step 13.
b.
If the resistance does not rise above 5000 ohms, the MCB is defective.
12. One at a time, reconnect the modem and each AOX-4 board (as applicable). Each time a
component is reconnected, measure the resistance between field terminals “DC-GRD” and “13
Vdc.” It should steadily rise to a value greater than 5000 ohms.
If the resistance rises above 5000 ohms, repeat this step until the modem and all AOX-4 boards
(as applicable) have been checked out. If the problem persists, obtain factory service.
If the resistance does not rise above 5000 ohms, the modem or the AOX-4 board just connected is
defective. (With the power plug disconnected, the resistance across an AOX-4 board’s “DC” and
“G” terminals should not be less than 3 million ohms.)
Figure 18. MCB Power Supply Terminals
POWER FUSES
[BUSSMAN GDC-T2A]
POWER IN
[18-24 VCT]
AC AC GND GND
4
3
2
1
9 8 7 6 5 4 3 2 1
Fuse F1
Fuse F2
a0115
AUX/OUT
Troubleshooting Analog Outputs
Variable voltage or current control signals are sent to analog outputs by the MCB through the Analog
Output Expansion Module (AOX-4). The MCB sends a voltage or current signal to the AOX-4 via a
ribbon cable. Jumpers on the AOX-4 determine what type of output is sent to the analog output
device. The analog output signals are sent from the AOX-4 by connecting a two-pin Phoenix
connector to the Analog Output Ports on the AOX-4. The analog output device also has an external
power supply, usually 24 Vac, that is not powered by the MAG.
Analog Output Device is not Operating Correctly
If the MCB appears to be functioning properly and the analog output device is not operating
correctly, perform the following procedure:
