I am new to owning a pinball recently I acquire a Black Knight 2000 one of the first pinballs I played as a child. I was able to LED parts of the playfield and wanted to start with some mods in the back box. I have the keys for the pin but when I try to unlock the back box the key works it seems not to go all the way to unlock it. Feels like there is something caught and the key feels bouncy which is causing the back glass not to be able to be removed. Does anyone have any suggestions for a newbie owner?