If worried about the converter, try another e.g. give a cheapy Aten UC232A. They work well…
Also, check the female pins on the Robo unit in case one is fully depressed. Jaycar sell some nice Deoxit too to give the pins a clean and gold coat… same on the male phone plug end.
https://www.jaycar.com.au/deoxit-con...n-kit/p/NS1436