USB Console session displays random characters.

[Point-Guard]

I am trying to connect to the PCB of a network switch that is currently in the R&D stage using a USB-to-console cable. However, the console session continuously displays garbled or random characters. Whenever I type a command, the input appears corrupted, with characters getting mixed up or replaced by random symbols.

For example:

r&oot@xyx# # he&0

I have tested all common baud rates. Only 115200 bps produces any readable output; all other baud rates either display a blank screen or a continuous stream of special characters.

To rule out software issues, I tested multiple terminal applications on different operating systems:

• Windows: PuTTY, Hercules

• Ubuntu (VM): Minicom, Screen

The behavior is identical across all tools and platforms. The console output remains corrupted, and typed characters are not displayed correctly.

[dehagart]

Do you have strong electrical fields or radiation emitters close by? Even the switch itself can do this if it is poorly shielded.

Those fields can induce a current in your console cable that can show up as garbled characters. 

[Leo Laohoo]

How long is the blue consoler cable?  Try using a console cable with 1 metre in length. 

Try using a terminal server.

[Point-Guard]

Cable is 1.5 metre in length 

[Leo Laohoo]

Cut the cable down to 1.0 metre (or less).

[Jens Albrecht]

Based on your description it does not look like a terminal-emulator based problem.

So it might be a faulty or incompatible USB-to-serial cable. Replace it with a known-good and working one.

[pieterh]

1) don't forget to check your other serial settings like data-bit size, parity and stop-bits (8,N,1 )
+ flow control off or Xon/Xoff

2) on the DB-9 connector of the USB-to-serial adapter "loopback" the TxD and RxD pins (2 and 3)  using a short piece of wire.
verify that  this way the typed characters are received correctly by the emulator.
if not than the usb-adapter (or it's driver) is faulty.

 you can do the same loopback at the end of the Cisco Blue console cable. RJ-45 contacs 2 and 6
(easiest if if you have a spare RJ-45 receptacle)