Check the convertor:

If there is an RS232 to RS485/422 converter being used, then check to see that it is setup correctly, things to check are:

Check the wires haven’t fallen out or broken off!
RS485: does the converter need to be set to 2-wire or 4-wire mode or is this done by jumpering across from Tx to Rx ?
Power requirements: Is the convertor’s power supply working? Check with a Voltmeter
LEDs: are there LEDs indicating comms traffic? Are they flashing Tx but not Rx? See here for a note on how often they should flash.
If the RS232/RS485 converter is self-powered, does the 9-pin port on the PC supply enough power? Some laptops don’t, and some USB-to-Serial convertors don’t.
If there are no LEDs on the converter itself, you can make some to verify that SpecView is talking out to the instruments, see here.
Does the converter have Automatic Send Data Control? If not, then it probably won’t work! See here for more details on this. Note: “KD485” convertors need to be “KD485 ADE” versions to work.

If there is a USB-to-Serial converter in use, you can check to see if that is working properly

SCADA software for people with other jobs!