Issues with serial display

I'm having issues with running the serial display I have (Matrix Orbital LK204-25) with my Uno.

I've determined that the serial TX on the Uno is a TTL signal and my LCD is currently set in RS232 mode, which is the signal I need to be in as I need this LCD to work with two different micro-controllers and one of them is only capable of RS232.

Problem being, that even when I hook up the Arduino to a TTL/RS232 conversion chip, I'm still getting garbage on the LCD. I thought that it may have been a baud-rate error but came to the conclusion that it's not after writing a program that tried to display something on all of the preset baud-rates of the LCD.

Any suggestions, ideas, needs for further clarification?

At least for Versio 2.0 of the display: "The display module communicates at standard voltage levels of -30V to +30V or at TTL levels of 0 to +5V by setting the Protocol Select Jumpers to TTL."

The LCD is currently set to operate on the RS-232 signal via the jumpers on the back of it.

The two micro-controllers I'm using are the Arduino Uno (which operates on TTL levels) and the M100 by Pi-Shurlock which only operates at RS-232. The Uno is our backup controller, so we need the LCD to operate on RS-232 for the M100, and the Uno to operate on RS-232 via a TTL/RS-232 conversion chip.

Has anyone else had an issue with trying to hook up the Uno to a RS-232 converter then to a LCD. I'm sure it's something I'm not doing correctly, I'm just wondering if there's a trick or something.

Thank you,

Normally backup systems are quite identical. So replace the M100 and use 2 Arduino uno's - one as main the other as backup. Or use 2 display's ...

Not sure what you are using to convert the TTL to RS232 (MAX232 maybe) but your problem might be that the serial signal needs to be inverted. NewSoftSerial version 10C lets you specifiy "inverse logic" i.e. inverted

NewSoftSerial(uint8_t receivePin, uint8_t transmitPin, bool inverse_logic = false);