Jupiter JF2 – Module Powered On but not sending anything on UART

3 thoughts on “Jupiter JF2 – Module Powered On but not sending anything on UART

  1. I’ve a JF2 module mounted on a board out of a production batch of about 150 pieces.


    Reference on the label: 1303FA7B01673.


    The module is powered on using ON/OFF and the SYSTEM_ON signal go high.


    Problem: the module never send any data on the serial port.


    It’s the only module out of the production batch that have this issue.


    I suspect a soldering problem, but I would like to have some help finding why it acts like that. Is there any diagnostic I can do in order to check the module is running well ?


    1. Hi,

      I have a very similar problem so I am adding to this thread.

      We have a fleet with several hundred units where the GPS (Jupiter JF2) is working fine. Now I had 2 RMA units where there was no GPS positioning. After troubleshooting I can see that:

      1. the GPS module is powered on correctly
      2. It gets the ON_OFF sequence
      3. SYSTEM_ON goes high
      4. I get a $PSRF150,1 message on the serial port

      On one unit, sending “cold start” ($PSRF101,0,0,0,0,0,0,12,4*10) will start the production of NMEA messages as usual. However, on the second unit this does not work. I have also tested to send factory reset ($PSRF101,0,0,0,000,0,0,12,8*1C) and enable RMC ($PSRF103,04,00,01,01*21) to the second unit with no success. It only sends $PSRF150 and then nothing.

      My question is what I can do to diagnose this problem.

      • What does it mean exactly that it only sends the “okToSend” message? From my understanding of the documentation, this means that the ON_OFF sequence was successful and the GPS has entered full power mode. In this case it should start producing NMEA 1Hz automatically, right? So what can cause it not to?

      The failing GPS modules are Jupiter JF2

      Serial number: 1247FA2D00399 and 1317FA2D05062

      We have an increasing number of complaints on GPS failure, so any help to figure this out is very welcome! Thanks!

      1. Hi,


        From the part number you report in the request, I see that those have a old JF2 FW release.

        Unfortunately what you are facing is a known issue called Random RTC at power up. Sorry about that.

        In this case, you have 2 possibilies:


        1. Use the official workaround, which is to give a COLD start to the JF2 ($PSRF101,0,0,0,0,0,0,12,4*10) after the $PSRF150 appears and no NMEA sentences are flowing.

        This will recover the situation and the NMEA sentences will start to flow normally from the module.


        2. Upgrade the JF2 FW to the latest available.

        Please note that this option is available only if in the customer board the JF2 BOOT pin (pin 17) can be managed, because in order to flash the JF2 the BOOT signal must be put high through a 10K pull up resistor to +1.8 volts.).

        Does the customer board have this possibily?


        Moreover, does the customer have an MCU connected to the JF2?

        Because customer has to implement the flashing protocol source code (which Telit provides under a specific NDA) inside their MCU, in order to do the JF2 upgrade procedure.


        As attachment you can find the deltaSW from your version to the latest available (4.1.2-P9)