4-4
A non-silenceable panel alarm usually means that the Master Controller does not
have +28V power. +28V originates from the Power I/O Interface
Uninterruptible Power Supply.
There is most likely a problem with the Standard Slave PCB assembly, Power
I/O Interface assembly or possibly, a cable assembly. There is a possibility that
the problem could be related to the Power Supply, but this assembly has
exhibited the fewest problems.
Perform the following checks:
• Check the Power I/O Interface-to-Standard Slave interface ribbon cable for
proper connection
• Check Power Enable jumpers on the Power I/O assembly to make sure that
they are not dislodged
• Check for proper Standard Slave/Power I/O initialization (see Table 5-1,
page 5-1 for the software initialization sequence)
• Check for an A-tap problem (see ‘Checking for an A-tap Problem’, below)
• If an A-tap problem exists, test for shorts or an overload condition by
disconnecting the power feeds to any extra system boards
Normally, power for devices located outside of the panel is
provided by the B-tap and this line should be fused as described in
the 4020 Field Wiring Diagram P/N 841-842. Although not
recommended, sometimes power is pulled from the A-tap, which is
normally already heavily loaded.
If A-tap power is essential for external devices, it should be fused
the same as the B-tap.
To check for a problem with the A-tap, measure both the A-tap and the B-tap
voltage at the output terminals on the Power I/O Interface board. Both should
read 28.5V ±.2V.
If the B-tap is OK and there is no A-tap voltage: there is an A-tap problem.
If the B-tap is not the correct voltage and there is no A-tap voltage: there is
a power initialization problem.
If a “All cards show missing/failed” trouble is observed, the A-tap is probably
bad.
If an A-tap problem exists, test for shorts or overloading by disconnecting the
power feeds to any extra system boards.
Normally, power for devices located outside of the panel is
provided by the B-tap and this line should be fused as described in
the 4020 Field Wiring Diagram P/N 841-842. Although not
recommended, sometimes power is pulled from the A-tap, which is
normally already heavily loaded.
If A-tap power is essential for external devices, it should be fused
the same as the B-tap.
Continued on next page
Troubleshooting Procedures,
Continued
If the Panel Alarm is sounding
and can not be silenced
Checking for an A-tap
Problem
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