BB2 reel cabinet - how to remove backplane?

[Parsonsaj]

I am fairly new to slots but have worked on pinballs for a long time…

My Alice & the Mad Tea Party cabinet doesn’t have any functional comm ports so I figured a backplane switch would resolve that.  However I can’t seem to figure out how to remove the old backplane to replace it!  The backplane board itself has 4 screws that attach it to this metal frame/cage, but removing those screws does not release the board.  I tried to loosen the 3 nuts that seem to hold the entire frame in place but I couldn’t move the frame either. What am I missing here?

Thanks!

[Chris-socal]

Images need to be 1Mb or less each max 5 per post.
I use an app called Image Resize, others here email the pictures to themselves and let the email application compress.

Chris