5150III 50 Watt PCB Removal

Embarrassing, but I can't get the main PCB out. I know it sounds ridiculous, but I had to just take a break before a damaged something. Anyway all the necessary spade connectors have been disconnected, retaining nuts off the pots and 23 (labeled ST1-ST23, so I thinks that's all of them) PCB mounting screws have been removed. I also took out the loop/headphone PCB for easy access and three top mounted heatsink screws. When I lift up on the back of the PCB it lifts easily, but seems to be stuck in the center of the board, like around V5 and V6. Anyone experience this? Am I missing fastener or is there some kind of glue holding this? Any assistance is appreciated. Thanks.

is there a filter cap on the outside of the chassis - if yes could be connected there.

Thanks for the post. It was the preamp tube sockets locked into the chassis cutouts. The control faceplate fit tightly around the pots and basically nothing would move. Once you remove the faceplate (double-stick tape) you'll see the holes in the chassis for the pots are oblong. So that side of the PCB can be lifted up and the sockets are freed. Actually a pretty smart design once you understand it. Thanks again.