No GSM signal due to shorted MMCX Connector?

Hi,

I have a problem in getting my WaveCOM Q64 GSM modem to register to network here, despite trying with a number of GSM external antennas. The signal strength returned by AT+CSQ is always 99,99, which means no signal. After some troubleshooting, I found out that there is a continuity (short circuit) between the centre pin and the surrounding of the MMCX connector. Could this be the problem?

Thanks

KHTong

I think you're on the right path. Generally, you won't have RF connectors with a DC short to ground. Start by checking where the connector meets the PCB. It's possible that there is a very small solder bridge between one of the four GND pins and the center pin (use a microscope to inspect). You might try reflowing the solder on all 5 pins, to remove any thin whiskers of solder bridging the nodes. The short may also be under the connector body, so you might need to remove the connector to find it. If the connector is removed, check the connector by itself for a short, then check the PCB by itself.

Also, look at how the connector meets the PCB. The center conductor could have a wide pad that overlaps, and touches the ground pads on the PCB.

Thank you for your suggestion.

Hello, I hope you can help me... I got a Q64 GSM/GPRS modem, I'm able to connect to it using the hyperterminal but I can't get it attached to the network so I can start sending info. Something curious is that when modem is on, the SIMVCC pin remains at 0v level, but when I issue an AT+CPOF command and the modem turns off, the SIMVCC goes to 3V? any sugestions?
thanks in avance.

It turn out that my problem was due to wrong frequency band used by the Q64 GSM modem. After I changed the frequency band using AT+WMBS command (to the one used by my local network operator), my Q64 GSM modem worked perfectly. You may want to check this with your Q64 modem.

Hope that helps.

Kok Hua