Welcome to the Forum, @ramm440! 
I didn’t have any luck searching for Nutone 1991 when trying to figure out what kind of chime you have, so I’ll just dive in with a bunch of follow-up questions to try to better understand your situation:
- What is the exact model of your doorbell chime? If you can provide a clear photo, preferably something showing the terminals and wiring, then that could be helpful.
- Is your chime compatible according to the Help Center article?
- Are you actually trying to use Video Doorbell v2? Your tags and topic title aren’t entirely clear, but I think that’s what you’re alluding to here.
- What were you using for a doorbell button prior to installing Video Doorbell v2 (if that’s what you’re using now)?
- Was the chime working before?
- What was the rating of the transformer you were using prior to replacement?
- What measurement/testing have you done while troubleshooting (e.g., measuring voltage at the transformer and at the doorbell button’s location and comparing that to the transformer’s rating, tracing the wiring to ensure that the correct wires and terminals are connected, etc.)?
- I’m not sure what you mean by this, so what additional explanation can you provide?
Other community members may have additional questions, but this is where I’d start in order to get the lay of the land.
I am not an electrician.