When I connect both receivers to an oscilloscope, I can confirm data on the Tx pin of the SAM-M8Q, as well as measure the baud rate. However, the Tx pin of the ZOE-M8Q measures 0V and never changes. Could this be due to the fact that the receiver isn’t configured to output data on UART1? None of the SparkFun ublox library examples (e.g. Example10_ResetConfiguration) appear to be able to resolve the issue. I should note that I2C communications on the ZOE-M8Q work properly, and the receiver outputs NMEA over I2C without any problems.
Are there any other ways of manually resetting the configuration of the ZOE-M8Q over I2C? Perhaps it could be a bad board?
You should be able to use the ZOE-M8Q over UART with an FTDI so either somehow that port was disabled or the UART output is not working properly. The [Factory Default-I2C Example from our u-blox library should reset the board so you can use it over UART in u-center. Have you tested the UART output with just a terminal program? The ZOE-M8Q will spit out NMEA data over that port so that would be another good check. Finally, just to eliminate the possibility of any weird hardware issues, can you please take a few photos of the top and bottom of your ZOE-M8Q and attach them to your response? Please do your best to make sure they are clear and well-lit.](https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library/blob/master/examples/Example12_FactoryDefault_I2C/Example12_FactoryDefault_I2C.ino)
I’ve run the Example12_FactoryDefault_I2C script already but unfortunately there’s been no change to the NMEA output (or lack thereof) over UART. I’ve attempted to communicate directly with the board over UART using [CoolTerm at 9600 baud, but again no output. The most telling sign is that the Tx pin always measures 0V when connected to an oscilloscope. By comparison, the SAM-M8Q happily transmits away and I can easily measure the baud rate of the data flowing over the Tx pin. With the ZOE-M8Q SiP package, it’s going to be difficult to visually assess what it could be, but I’ve attached a link to a photo below. My best guess is that there’s a dry solder connection underneath the SiP that could be causing the problem.
Thanks for providing that photo and the troubleshooting steps you have already taken. Since you are seeing no activity on the TX pin on a scope where other boards work just fine, I agree with your assessment that there is a bad solder joint or something else going wrong with that pin and we would be happy to assist you with a replacement. I believe you have already sent our Customer Service team an e-mail about this issue so I will reply to that with further information regarding your replacement.