Null-Modem/SerialPort on Amiga500 (build in 1988) doesn't work

[RiP]

I have the same problem with ADF Sender.
Hope someone can help

Hmm do you have a modem or anything to test the port? You may have a bad CIA chip causing the port to be dead. This  has happened to me in the past.

Are you sure? possible to check if the CIA is really dead or not?

[RiP]

As I said, my Amiga 2000 can receive files from ADF Sender but can't send to PC.
It was working fine last month but the COM port got bad in a day.
So I believe it's a hardware problem but need to know how to fix it?
My Amiga 500 works fine with the same cable.