Just built the JetBot according to the instructions on sparkFun, and when it boots up with the default SD card that was shipped with the JetBot, the qwiic OLED and motor drives does not work. I have tried to disconnect the motor drive, and the display is still just black.
If the motor drive is connected, a blue led will blink every few seconds.
In dmesg, the following error message is printed out every few seconds:
tegra-i2c 7000c400.i2c: no acknowledge from address 0x3d
I had a somewhat similar problem that turned out to be a bent CLK on one of the QWIIC connectors.
Just double-checked, none of the pins are bent…
I’m not sure I’m an expert, but I guess I can try to help.
What happens when you try to do the basic_motion notebook?
Did you try connecting directly to the motor controller from the pHat?
Maybe try a different connector or a different cable in case one is bad (I think the connectors are all on the same bus).
If you get past the
robot = Robot()
line in the basic_motion, I think that means it saw the motor controller (mine was crashing at that line when my CLK pin was disconnected).
The motors work.
Bought 6 sets from SparkFun, have built all 6 now, and the display works on four of the units, and are defective on two.
I’m also having issues with the WiFi adapter on all units. A lot of packets are dropped… 
Ok…
Just to give an update. My issues are solved now!
First issue, with the OLED screens as mentioned in the previous post, was actually because of DOA components. 2 out of 6 JetBot-kits we bought had defective qwiic OLED displays. The issue was solved by purchasing new displays.
We also had a lot of problems with the Edimax WiFi USB adapter. Connection with the browser (and Jupyter Notebooks) would usually fail after a minute or two, and ifconfig showed that a large amount of RX packets were dropped by the adapter. This was solved by throwing away the Edimax USB-dongles. Bought Intel 8265NGW M.2 cards with Molex antennas as suggested in the Nvidia JetBot BoM [1]. Nvidia also warns about an issue with the Linux driver for the USB WiFi dongles with the RTL8192U chipset [2].