Hi Guys
I have many of the PC 690 routers and HAD the same errors,,, PC have redone the clamp system on the PC routers,, that said ,,, it's hard to get them tight with the small wing they come with , if you rework the wing nut by putting a piece of hardwood over the wing nut that will take care of the error and you can get it tight or unscrew easy.
It's just some hardwood that's 1/2" x 1" x 1 1/2" with a mortis slot to put over the stock wing nut...then glued in place with super glue..
If you want to see a snapshot of it just ask and I will post a snapshot of it..
======