Yesterday afternoon, Jim Black showed me how to check a serial cable.
I was having trouble connecting to a board over a serial port, and thought it might be my cable. Jim showed me that if you connect pins 2 & 3, it will connect transmit to receive, and if you type at it, the characters will echo to the screen.
Here, Jim's connecting the pins with a screwdriver. When he first showed me, he used a pair of scissors that were lying around.
Jim says it's one of his "old man tricks."
He also taught me not to touch the case with the connector, since that will ground the connector and send my transmissions to /dev/dirt .
"Serial cables: the most non-standard standard, ever." -- Jim Black