Nexstar4 serial connection issues

So after being in storage for over 10 years I dragged out the Nexstar 4. Powered up though the screen is a bit dim. Did all the right things, set it to rs232, connected nexremote via a usb to serial adapter (which is working)

The screen on the app shows Initialising, then says: No Response 17, Invalid Model.

I've selected Nexstar4/5se, and gone into windows device manager to ensure the port is operating at 9600.

Any suggestions?