I accidentally broke the network interfaces (wireless and LAN) when trying to configure the wireless interface. My only option now is to connect to the Mastermind using the serial console on /dev/ttyS1. As I do not have a special cable, I had to make one by myself. I connected Rx, Tx and GND from UART_B (/dev/ttyS1) to a USB-Serial-adapter on my computer (Rx->Tx, Tx->Rx, GND->GND). I tried all different baudrates and only get nonsense. I also used different serial communication programs, such as minicom, putty, hterm, on Linux and Windows.
Is there something I'm missing?
your cable seems fine. The serial console on the Mastermind is on /dev/ttyS3, which is UART_D. The settings are 9600Baud, 8N1. I have tested it with Putty on Windows. Please note, that you need to disable flow control in Putty, as it is usually enabled there for serial connections.
The serial console on the Mastermind is only setup with our provided images, if you installed another OS on the Mastermind, you need to setup this console on your own.