RM520N-GL refuses to register since network outage 3 days ago

IoT Modules 5G Module
1

We had two network outages last week. Modem had difficulty registering after first outage but eventually did after restarting many times. Second outage was 3 days ago and unable to register since despite many hours of troubleshooting. I’m listing all the troubleshooting I have tried below. I hope someone can help.

Device:

  • Quectel RM520N-GL
  • Firmware: RM520NGLAAR03A03M4G
  • Host: OpenWrt router running ModemManager initially, then switched to QMI and PPP
  • APN: mobile.o2.co.uk and payandgo.o2.co.uk tested
  • SIM: Confirmed working in another LTE router (TP-Link MR600), same location and network (O2 UK)

Current Issue:
Modem fails to register to network and returns +CREG: 0,0, +QNWINFO: No Service, and +CSQ: 99,99 intermittently. Connection attempts via ModemManager, QMI, and PPP all fail or immediately drop. AT+QMBNCFG="Activate" consistently returns ERROR despite selecting valid profiles.

Troubleshooting Steps Attempted

1. Modem Detection

  • Modem is correctly enumerated:
    • USB ports: /dev/ttyUSB0–ttyUSB3 present
    • /dev/cdc-wdm0 visible (but no /dev/wwan0)
  • mmcli -L and mmcli -m 0 initially worked
  • At later stages, ModemManager failed to connect to DBus or lost access to the modem

2. SIM & Signal

  • SIM is known-good and unlocked (AT+CPIN? → READY)
  • Tried swapping SIMs and verified alternate one works in a separate router
  • AT+CSQ results ranged from 22,99 to 99,99 (fluctuates)
  • AT+COPS=? failed with +CME ERROR: 100 or ERROR
  • AT+COPS=0 and AT+COPS=1,2,"23410" failed or timed out
  • Modem stuck in +QNWINFO: No Service or +CREG: 0,0

3. Profile / MBN Config

  • Listed all available profiles via AT+QMBNCFG="List"
  • Attempted to activate multiple profiles:
    • AT+QMBNCFG="Select","ROW_Commercial" → OK
    • AT+QMBNCFG="Activate" → always returns ERROR
  • Tried deactivating first: AT+QMBNCFG="Deactivate" → OK, but no change
  • Checked currently active profile via AT+QMBNCFG="Active" → returns ERROR

4. Reset & Reinitialisation

  • Used AT+CFUN=0 followed by AT+CFUN=1,1 to reset modem
  • Power-cycled the router and modem several times
  • Enabled debug output with AT+QCFG="dbgctl",1 (if supported)

5. Protocol Modes

  • Initially used ModemManager with proto=modemmanager — failed to bring up interface
  • Switched to QMI:
    • Interface wwan in OpenWrt configured for QMI, APN mobile.o2.co.uk
    • Logs showed:
      • Device does not support 802.3 mode. Informing driver of raw-ip only
      • Network registration failed, registration timeout reached
      • Permission denied errors on ubus calls
  • Switched to PPP on /dev/ttyUSB3:
    • Chat script established connection
    • CHAP auth succeeded
    • PPP session immediately disconnected (Modem hangup)
    • Tried setting APN PDP type to IPV4V6 using AT+CGDCONT=1,"IPV4V6","..."
  • Attempted to change USB mode to QMI:
    • AT+QCFG="usbnet",1 → OK
    • Still no /dev/wwan0
    • AT+QCFG="usbcomp" → returns ERROR
2

@echoorbit37

Just for a little more details.
What kind of adapter is hosting your RM520N-GL? Any chance a component on it,may have flaked out. Do you have another adapter you can canabolize from something else in your stack to use with this modem.
Maybe be barking up the wrong tree.
Yours truly is guilty of this,about 1,000 times.
If you dont have a second adapter to try,my next guess would be reflash your RM520N-GL
back in the day,what i found is,if you had two,three real quick,power blips in the building it was alway curtains for one or two items,you could bank on it.
Good Luck!

1 Like
3

It’s connecting through the m.2 interface of the BPI-R4 (which is almost brand new so hopefully not that!). I do have a usb interface I could try it with which would be useful in ruling that in or out. I’m also going to pick up a sim from another provider tomorrow just in case somehow my provider has taken a dislike to this modem and is blocking it from registering. After 7 solid hours of troubleshooting today I will try anything!

4

You are getting “permission denied on ubus calls”?.. Just noticed this,this is most likely your problem,not the modem itself… Did you compile the image to burn on to your BPI?,Or a prebuilt image, would bet this is your prob,Good thing you dropped your error log here…
previous to this it looks like registration failed, but this is very deceiving.. have run into this myself in the past.
these things will drive you to drink!
I would reimage your PI,to be honest.. If you had power blips,ill bet your image got kabashed..
May want to spring for a good UPS for the BA PI. I always hated UPS’s until got one for home use. Youd be surprised how many times in a month,this thing chirps,from electric lowness etc.
Also,am sure you have done it,but if,not physically take the modem out,hit power button couple times,put back in the PI slot.

Good Luck!

5

The outage was the cellular network, not the power so there has been no power issue to the BPI.

6

Is there any admin from Quectel here who can look at this for me? I have tried a SIM card from another network and get the same response. I am concerned there is a hardware issue with the modem.

7

Try AT+QCFG="ResetFactory"

This will reset all settings and it might work? This is what I usually do to clear APN settings when swapping SIMs but it might help in your case if it’s setup wrong. Once this is done the CGDCONT table should read from the SIM instead of modem memory

8

@echoorbit37

Place your log here again,when trying to connect to your operator.
Try about three times.
It may decern some clues what is failing as of now.

9

Dear @echoorbit37
Did you check your hardware?
After reset modem or power -cycled, do you see device search the network?