I'm trying to do the same thing, I think, and I can't get it to work.
I have a dropdown box to select the type of weld: groove or fillet.
There are several other dropdown boxes with various weld parameters. If fillet is selected in the first box, I want the groove parameter boxes to be filled with "N/A". Likewise, if groove is selected, I want the fillet parameter boxes to be filled with "N/A".