module #2 is the microwave loop assembly (A11 module) that's as much as I can tell from memory
it could be that the microwave loop needs adjustment and the DACs are hitting their limits at the moment
or it could be other problem
if you run the instrument diagnostics as per service manual and do the follow up tests (specially the special function
that lets you check the MUX values on that module and compare with the expected values in the service manual)?
usually can narrow down the issue.?
In the end you might as well get to component level troubleshooting but first it should be established which module is causing the unlock?
