The Rambo/RamboMini have built in fuses to protect the board. There are three fuses total, two 5A and one 15A. You likely hear a small "pop" sound and the board has lost all its functionality.
These are automotive fuses and can be found at any local auto parts store. To be sure, bring the fuse with you and make sure to get the correct value fuses (especially for the heated bed one). Be sure to place the new fuses back into the correct positions.
RamboMini photo below for reference. (Fuses are located at F2,F3,F4)
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