For reference, these are the boards I am referring to: GPS-15136 https://www.sparkfun.com/products/15136
We have recently purchased two of the above GPS-RTK2 boards. Both boards arrived fully functional with no problems. No modifications were performed on either board.
One day I was working with both boards plugged into my laptop’s docking station doing general configuration using u-center. I un-docked my laptop and proceeded to unplug both GPS RTK devices.
The next time I plugged the devices back into the USB ports, I was unable to initialize a serial connection in u-center or any other serial interface (I am using the correct COM port and baud rate of 9600). The device still enumerates and is assigned a COM port. The drivers are correct (USB SERIAL DEVICE). I am still able to send and receive commands via I2C.
After some testing I discovered that if I put my computer to sleep, turn it back on + log in, then I can connect to the device for ~10 seconds. Looking at the package console in u-center, we can see that I am receiving serial data. A snippet of the data looks like this.
18:18:09 R → NMEA GNTXT, Size 37, ‘Text Transmission’
18:18:10 R → NMEA GNRMC, Size 36, ‘Recommended Minimum Specific GNSS Data’
18:18:10 R → NMEA GNVTG, Size 21, ‘Course Over Ground and Ground Speed’
18:18:10 R → NMEA GNGGA, Size 42, ‘Global Positioning System Fix Data’
18:18:10 R → NMEA GNGSA, Size 47, ‘GNSS DOP and Active Satellites’
18:18:10 R → NMEA GNTXT, Size 35, ‘Text Transmission’
18:18:10 R → NMEA GNTXT, Size 37, ‘Text Transmission’
18:18:10 R → NMEA GNTXT, Size 37, ‘Text Transmission’
This led me to believe that the serial port on the ZED F9P was actually functional but the ESD protection IC was damaged. According to the datasheet the PRTR5V0U2F is an ESD protection IC consisting of a network of diodes and a 5.5V Zener diode to clamp the supply voltage to 5.5V.
Measurements were made using a multi-meter in diode mode. The diodes between pins 2 and 6, 1 and 5, 2 and 4, 3 and 5 all behave normally with a forward voltage drop of ~0.7V and an open circuit condition in reverse bias. However the Zener clamping diode, with a reverse breakdown voltage of 5.5V yielded incorrect values. The diode has a forward voltage of 0.57 V (totally fine, but not important in this scenario) and a reverse breakdown voltage of 1 V. This measurement leads me to believe that the protection circuit is interfering with the serial data which would make sense since I can receive broken serial data from the port.
Is there any chance this is covered under warranty? Like I mentioned earlier, we have not modified the boards or performed any rework and the problems arose under normal use conditions.
Thanks in advance!
