Onboard mic not working when in Zoom

Has anyone found a fix for a "mic not working" when in Zoom. I can use and external mic and then zoom attendees can hear me. Speakers are working. The onboard mic works when doing dictation in Word, in Skype and when I used the online "mictest.com".  It's only on Zoom that it's an issue which started about 1-2 weeks back I think when an update came out. 

Paul49