Quectel RM502Q-AE

[CK25Hulk]

Hoping someone can assist.

I have a Quectel rm502q-ae modem in a Wi-Fix WG1608 router with a 4x4 Mimo panel antenna off a mast from the chimney that had been working great for us. Using Calyx T-Mobile. Haven’t touched any settings in 10 months. For some reason last night the unit dropped the connection and as of 3 pm (EST) time, it is still down. My best attempts to reset the connection have failed. Usually, reboot/pull SIM and cycle it that way. It boots up as normal but the splash for the router stats screens illustrates “No Modem Present” Eventually after 10 minutes it responds with

"Can't open device /dev/ttyUSB2" in the Modem description on the splash screen

Then does provide the RM502Q-AE modem name. With the SIM in or out of the unit everything to the best of my knowledge appears working, all of the bands are selected and when I search it comes up with half a dozen options. I've tried targeting a band with the SIM in and it doesn't make a difference in updating Strength, CSQ, RSSI, RSCP, and SINR numbers they remain blank.

The Quectel is powered through a battery backup to prevent any loss or spikes of power. In frustration in trying a last-minute test, I removed the sim and put it into a hotspot MoFi2000 unit, and to my surprise I can regain a connection. The only downside is that it is poor for whole-home use. The unit just doesn’t have the power to broadcast the Wi-Fi signal throughout the house. For the Wg1608 unit, I have Ethernet cables tied to the rest of the house.

Any thoughts on what to do to get the Quectel modem working again?

[BillA]

Some diag steps I would try....

Re-seat the modem and tighten the screws.
Re-flash the modem.
Re-flash the router.
Try another spare/borrowed modem.
If all else fails, smoke a Wireless Joint to go to Wireless Heaven. lol

[CK25Hulk]

I pulled the modem and reseated it back to the board. Powered everything back up and the modem shows as connected however the Provider states it is Connecting as shown in the illustration below. Doesnt' resolve past this point. The modem/router is finding bands that it scans in my area but something is hung up on the connection. Using TMobile/Calyx currently, any next steps.? I am puzzled as to why everything came to a stop with this issue when it had been working for months. I read some earlier threads about some AT commands but I am unsure which ones to run. If there is a tutorial on how to do this and which commands to run, that would be helpful.

[BillA]

I pulled the modem and reseated it back to the board. Powered everything back up and the modem shows as connected however the Provider states it is Connecting as shown in the illustration below. Doesnt' resolve past this point. The modem/router is finding bands that it scans in my area but something is hung up on the connection. Using TMobile/Calyx currently, any next steps.? I am puzzled as to why everything came to a stop with this issue when it had been working for months. I read some earlier threads about some AT commands but I am unsure which ones to run. If there is a tutorial on how to do this and which commands to run, that would be helpful.

The original error "No modem present" was probably fixed by re-seating the modem.
Next, I would test the sim card in a phone to make sure the service is working properly.
If you're able to call and browse a web on a phone, then the carrier may be blocking the modem by its imei on the router.
To fix that, you could try entering some special AT-commands which can be found by searching the dark side of the interwebz. heh

[Tech_Junky]

test the sim card in a phone to make sure the service is working properly.

The SIM is provisioned and working per testing in the MOFI.

@CK25Hulk
The way I'm seeing this is something glitched in the modem itself or see below. I use my SIMCOM in a USB sled and while it works fine there are times when I'm messing with commands trying to tweak things it just rolls over and plays possum or just doesn't perform well.

There are plenty of commands though that can be run though to clear things up. My guess though based on the latest screen grab is there might have been a cutover on the cell site to another band or something if you had a band lock on the modem.

AT&F - reset / default
AT+CSYSSEL - restore all bands
AT+CEREG? - verify registration

I know SIMCOM / Quectel vary a bit in the command syntax though but, these should be fairly universal though.

[Tech_Junky]

Connecting

I just use a minicom session through my Linux box that my modem connects to in order to probe the modem directly.

Code: Select all

minicom -b 115200 -D /dev/ttyUSB2

This gets me to the AT terminal on the modem. While some GUI is useful it's much better to directly interface with these modems to figure out issues. Looking at the minicom command though I'm thinking you could use Putty to interface with it using the serial option w/ the baud 115200...

This is why I avoid using these oddball devices and setup a PC as a router instead. It's easier to track down the gremlins. Hopefully running the reset to default command will clear the issue of any band locking being the potential issue. If it's not a site upgrade that knocked you offline then it's potentially the modem itself having an issue. It's possible maybe it got hit with a FOTA update or something (not likely but possible).

[CK25Hulk]

Here is a speed test I captured this morning on my MoFi2000 unit when I swapped the SIM from the Quectel unit.

The SIM appears good and working. I'll give those AT commands a try. I appreciate the help!

[BillA]

Here is a speed test I captured this morning on my MoFi2000 unit when I swapped the SIM from the Quectel unit.

The SIM appears good and working. I'll give those AT commands a try. I appreciate the help!

Try swapping the modems too and see what happens in both units.
The best way of diagnosing an issue is by the process of elimination.