3470 microphone input problem

My setup with Zoom doesn't work properly and I'm having the same problem with another 3470. A webcam with Mic when plugged into the rear pink socket shows activity on the volume scale but on a Zoom test there is no response implying the input is dead which it isn't. The output tests fine into the local speaker. I've checked all the various driver settings and all the drivers are up to date. A similar install on a Dell laptop works fine. The implication is a driver/hardware issue with the 3470 system needing a driver update or whatever. Any thoughts?