determine the root of the problem
To find or ascertain the cause of a particular problem or issue. The plumber has determined the root of the problem, and it doesn’t sound too costly to fix, thank goodness.
*root of the problem
an understanding of the causes or basis of a problem. (*Typically: determine ~; figure out ~; find ~; get to ~; get at ~.) It will take a little more study to get to the root of the problem. Let's stop avoiding the issue and get at the root of the problem.
bound and determined to
Firmly resolved to, as in He was bound and determined to finish the assignment before taking on another. This phrase is a redundancy used for emphasis, as bound and determined here both mean "resolved to." Also see bound to.