Problems with the serial connection of a vintage HP plotter

Hello!

first of all I am not sure if this is the right place to post this so apologies if it isnt and ill delete it.

I recently gotten a vintage HP draftpro DXL 7575A plotter and ive been trying to get it to work on my windows 10 machine.
It has a serial RS-232-C port on the back and im using a serial rs-232 to usb converter to connect it to my PC.
But when i use the terminal to send commands I receive nothing.

I installed and reinstalled the drivers of the converter. and confirmed it worked because i shorted the RX and TX pin and i got a feedback loop.
The plotter itself also isnt the problem because everything on it works. the demo plot works fine and so do all the buttons.

so it must be a connection problem. and thats where im stuck.

the code im sending is HPGL which is easy to send a few commands.

the code:
IN;
SP1;
PA2000,2000;
CI500;

which means it initialises the plotter, picks pen 1, goes to coordinates 2000,2000 and draws a circle.

I checked the manual if i put the DIP switches in the right spot and the BAUD rate is correct

manual: HP Computer Museum

I also added some pictures of the back and the cable im using.

Thanks for reading all of this!
Damnub

I ran one many years ago but had a COM port on the PC, it may need to see the hardware handshake, which, if you have a COM port cable they can be jumpered out.
It may pay to see if you have a COM port connection on the MoBo as many modern PC's have it, but do not bring it out to the exterior.
Al.

unfortunately i dont have a serial port on my MOBO. I looked into the serial port PCI's but they are expensive (50 euros). the hardware handshake might be the problem but I dont have any knowledge about it. I read that i might need a null modem. because i dont know if the plotter is DTE or DCE. So I bought that and its comming in tomorrow.

So an update!

I got the null modem in the email and now im receiving something in the Com port:
picture: https://i.imgur.com/vJXh2Tc.png

this is turning the plotter on. waiting, and turning it off. (after the DSR Turned on ... )

I am playing around with the bBaud rates and Parity settings and that seems to chance the encrypted code (000 063 063 063 063 063 063 ) but I am not sure what it means.