What’s wrong with these McIntosh Monoblocks?

Evening, got a question about these two McIntosh MC40 amplifiers. I got them from garage type environment, humidity was present as they have some surface rust, but absolutely no damage or dents. Opened them up and did a visual inspection, nothing looks burnt out or bad. However, I replaced the fuses as they were both burnt out with ones that were identical, ensured the voltage setting was correct, plugged the amps in(no speakers connected), and nothing. Removed the fuses to find them both burnt out again. What could be causing this? Would be eternally grateful to anyone who can help.