We have been using a V5 brain since November, and as of now, we’ve broken 7 ports. We noticed that these broken ports were connected to long wires, with one of them measuring in at 6 feet long. These wires were connected to our Vision sensor and our cap flipper motor. Later, we got a replacement for our broken cortex but, even after minimal running, broke another port on the replaced Brain.
This is really serious because we’ve broken and 8 ports on two different brains, suggesting that this is most likely a design issue. We searched the forum for a possible root cause but no one seems to provide a convincing answer (ESD or long cable). As a result, we decided to look into what is broken within the port, either the RS485 (serial communication) or the power to the motor.
First, we wired a parallel cable to a motor connection so that we could look at the signals with an oscilloscope and voltmeter. Below is the picture of the wiring of the RJ22 connector.
Here are the likely signal definitions of the 4 wire V5 cable.
Red - Ground
Yellow - 12V Power
Green - RS485, negative
Black - RS485, positive
Below is an oscilloscope capture of a working V5 port. Yellow (Channel 1) is connected to the green wire, and Cyan (Channel 2) is connected to the black wire. The ground of the oscilloscope probe is connected to the red wire. Finally, a voltmeter is connected to the yellow wire referenced to the red/ground wire.
The voltmeter reads 12V.
Next, we used the same setup to connect to a broken port. Here is the oscilloscope capture.
In this case, the voltmeter reads 11V.
Looking at the two captures, the cyan trace of the working port goes up to 2V, while that of the broken one remains at ~ -0.5V. The yellow traces have similar differences in voltage between the broken and working ports.
Based on these two results, it looks to me that the communication IC, and not the power supply IC, is broken. We would greatly appreciate any input, findings or discussion from VEX or other teams concerning if these results point to ESD or the use of a long wire. Thanks in advance!