Hey, I have an old Yamaha PSS-470 that is not circuit bent or anything, it's my mom's from the 80s.  I have been having a blast with the synthesizer, moving the sliders up and down rapidly.  However, the spectrum slider stopped registering at the 3 position.  So I started deconstructing it to see if it was fixable.  However, I ran into a problem trying to detach the circuit board.  Try as I might, it would not come off, something was blocking it.  Has anybody deconstructed one of these and know what I'm talking about, is there a trick to it?  Thanks, any help would be much appreciated.