The 2 buffers for the CTS line is for the future, because on the RX line the 2 buffers worked with me.
Of course I have checked the resistors, the value, the diodes and the mosfets, measured them and it is okay. I did that many many times. I even checked the PCB for cracks in the cupper lines. But ...

I finally solved my problem.

Despite the Z80-board high level is 4.5 volts provided by an MC6850P ACIA (I can't measure the voltage in low-state) it didn't work.
For my radio-hobby I have a MFJ1270 packetmodem, and while it is called TTL-level, the high-level was 3.3 volt, and the low was about 0.6 ...

By the way: I have the Versaterm V1.2 PCB, while I noticed version 1.0 on github.
Does anybody know the difference between them? I've googled on the internet but I can't find anything about this.
Which PCB-version do you use?

Thanks all for the reply.
I think there is something wrong with the level of the Z80 board, despite working on the other ascii terminal.
I connected the output from the Z80 board directly onto the 9pins serial port and Versaterm shows something more, so I have to look for something else with a TTL ...

I've also made this Versatherm. But I have a strange issue. If I connect RX and TX with a jumper, the Versatherm echoos my keys on the screen, so I suppose it works good.
If I connect a board, e.g. my Z80-retro-computer which works great on the ASCII VT100 video terminal of Geoff Graham, I don't see ...

Let me introduce myself: my name is Adriaan, I live in the Netherlands, I am a licensed radio amateur, and I have been involved in electronics all my life.
In recent years, I have focused more on arduinos, Raspberry Pi's, and funny and useful applications of them.
The forum about the VersaTherm made ...