The following articles cover Bullhorn Remote Monitoring Units troubleshooting and other issues:
APM4AM-SAT: Unable to Send a Test Packet
APM4AM-SAT: Test Packet Does Not Include Data
APM4AM-SAT Sends Two Packets
Bullhorn Information Line
Changing SIM Cards in Bullhorn GSM Units
How Can I Detect the Loss of Primary AC?
Installing the IDP Satellite Terminal to an RM4012
Matching the RMU with its Satellite Terminal
Recommendation: Set Schedules First
RM4010 Satellite Terminal Set Up
RM4010 DC Input Shows Reading When Not Connected
RM4210 Wiring Guide
RM4211 Wiring Diagrams
Troubleshooting a Unit that Is Not Charging
The Remote Monitoring Unit is Not Clicking
Troubleshooting the APM4AM-SAT WS in Alarm
Troubleshooting Transmission Failures or Incorrect Readings
Understanding the LED Lights on RM4150 and RM4151 Units
Using Ferrite Filters With GSM Units
Why Use a Ferrite Filter in GSM Units