Sequential circuits samplers

Hi fellow users,

Due to transport mishandling I have to open up my 'new' Prophet 2000 
and try to remove a dent on the metal chassis from inside.

I removed the 3 screws from the left and right side and the similar 
screws (the upper screws)on the back of the machine, but I can't open 
it. Should I remove some screws on the bottom? If yes, which screws 
should it be? The 2 big screws or the smaller ones?

I'm afraid by unscrewing wrong screws that I'm doing something to the 
PCB's inside, so a step by step guidance would be appreciated :-)

Best regards

Brian