Hi all! After reading a number of topics on this forum regarding serial connection problems, I hope for some help.

I have brand-new RB1100AHX4. I have used it for 2 days. It works great, and I was able to update the firmware via Netinstall. Current firmware version: 6.43.7.

The main problem is that I absolutely can not connect to the serial port.

Here are all the cables I used.

In my dmesg I see: Product: FT232R USB UART or FT231X USB UART. Also, I tried one USB-Serial Controller by Prolific Technology.

As for the software, I have used minicom and screen on last Debian/Fedora 29, and Putty on Win7. I 've used only recommended settings, i.e.:
In all cases I see the same thing, namely the empty screen in Putty/Minicom/Screen. I also tried to reboot the router and watch what was happening on the screen. But nothing happened. Obviously, this is abnormal behavior.

In the case of one of the blue cables, I was able to enter some garbage characters (but did not see the normal command prompt). And later, after logging in with winbox, I saw warnings about login errors with incorrect characters.

My questions:

1.) Should my cables work? Can you suggest a specific cable model (and where can I get it) that will work exactly? (I wouldn't want to go through a lot of cables hoping to buy the right one).

2.) Is it definitely a breakdown and can I contact the seller for a refund?

3.) I can list ports using:

/port print detail
/system console print

And I can access it using:

/system serial-terminal

Are these facts evidence of serial port health and the absence of a breakdown?

I had to get console cable with something called "RS232 Level Shifter" in order to connect my 4011. Cables withouts it resulted in the same behaviour you describe, i.e. no output at all or garbage. FWIW, here is the one I got https://www.amazon.ca/gp/product/B07D54BQ92.