Hi,
I just spent a lot of last week trying to access the console of an old datacenter switch. I made a cable from the pinout of a similar switch.
My switch is a Dell S3048-ON this was for a C9010, it turned out to be correct.
So I tried over and over to make it work, but kept getting this garbled mess, but the mess was consistent with the rythm of a booting switch, and it kind of always looked the same
With many of these, I have many spares I thought they were broken, but they were not
I checked the signals with oscilloscope they were, dirty
So I made the signals cleaner by tidying it up
But still, it is a mess of garbled text !
Here I am using the other kind of serial adapter, this one serial to ethernet
Here is two runs, still garbled
As a last ditch attempt, I remembered one my old server has a real serial port !!
And it worked !
message continued in comment
I suppose the first question is whether you had the baud rate set correctly. The photo of the "cleaned up signals" (not entirely sure what you did, compared to the prior photo) seems to show a baud rate of 38400, given that each bit seems to take about 25 microseconds.
As for the voltage levels, the same photo seems to show 5v TTL. So it doesn't seem like you would need a level converter from 15v RS-232 levels. This is one of the few times where the distinction between a "serial port" and an RS-233 port makes a difference, but a lot of data center switches will deal using 5v TTL, because the signals aren't having to travel more than maybe 5 meters