yep, corrosion in connectors will do it for sure.
usually when you replace the main components and that doesn't work then you go to the troubleshooting wiring and power path's.
the thing about corrision is once it's in there it's hard to get rid of it unless you replace all the terminals with new ones. If this tech did not do that then the problem will more than likely return one day.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.