'Power Rangers' Jason David Frank

The late "Power Rangers" star Jason David Frank's karate school has allegedly fallen way behind in rent since his death ... and now the landlord is taking the school to court.

According to the docs, obtained by TMZ, Jason's Rising Sun Karate in Valencia, CA is getting sued by Valencia Marketplace, the shopping mall where the dojo's located. The suit claims Jason and co. are tenants under a couple of leases -- the original of which dates back to around 1998.

Sam Sprague

The problem, according to the docs, is that Rising Sun stopped paying rent around November and December 2022 -- you'll recall, Jason died on November 19, 2022. Valencia Marketplace says it served the company a written notice of…