A flash light and meter should be your "vehicle tool box" for the next little while so that when the occasion calls for it, you are ready. Since you have have had multiple hdm replacements, have you actually ever did an "autopsy" on a failed unit to see what's up... of course, you can always compare your "investigation results" by checking against a working unit. Depending on the depth and measurements, you might have your answer. Further though, it depends on what kind of module you are using for a replacement as most would say here that OEM is needed (even a used one) as the "power switching FET" in the module is usually the "weak link".