Invalid Replies From All Devices On Every Slc Loop; Intermittent Invalid Reply - Pittway NOTIFIER AM2020 Troubleshooting Manual

Invalid Replies From All
Devices on Every SLC
loop.
Intermittent Invalid
Reply.
12
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compensation errors when the power is reapplied. Correct compensation
levels will be restored within five days.
If every device on every SLC loop is in a constant invalid reply condition, this
may be a symptom of a bigger problem common to all the Loop Interface Boards.
The 24 VDC bus originating from the main power supply may be loaded down to
the point that it can no longer support proper operation.
Corrective Action:
1) On the MPS-24A Main Power Supply, with the main power harness or
harnesses plugged in, measure with a voltmeter either Plug P2 or P4,
pin 1 (-) to pin 7 (+).
Common (Pins 1-4)
5 VDC (Pin 8)
Original MPS-24A
Figure 2-10: The Upper-Right Corner of the MPS-24A
2) If this voltage reading is well below 24 VDC, power down the system and
disconnect the harnesses from P2 and P4.
3) Wait five minutes. This will allow any PTCs (Positive Temperature Coefficient
thermistors, a self-restoring circuit breaker device) on the main power supply
to self-restore if they have been tripped.
4) Reapply power to the system and measure pin 1 (-) and pin 7 (+) of P2 or P4
again (with the harnesses disconnected). If 24 VDC is not present, the main
power supply must be replaced. If 24 VDC is present, then something else in
the system is loading down this 24 VDC bus. Refer to the current calculation
tables in the AM2020/AFP1010 manual for further information.
Corrective Action:
1) An intermittent invalid reply may be caused by noise. If the SLC loop wiring is
shielded, make sure the shields are terminated properly, refer to the AM2020/
AFP1010 Manual for specific information.
2) Check the times that the invalid replies come in. Do they correspond to the
startup of any electrical motors or other possible sources of noise?
3) If the device that is producing the invalid reply is a Control Module or XPR-8
point, then the source of the invalid reply may be the wiring attached to this
device. Remove the field wiring and see if the invalid reply comes back.
AM2020/AFP1010 Troubleshooting Guide 50432 Revision A 8/13/97
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24 VDC (Pin 7)
Revised MPS-24A
24 VDC (Pin 7)
Common (Pins 1-4)
5 VDC (Pin 8)