same here... don't have to remove anything to get to the fines box other than the wingnut in the Pseries Harmans [ unless P38 is different,Assuming earlier Harmans had the fines box. Below those controls where you took the access panel off, get down on the floor with a light and look up in there. You should see a rectangular box with a metal cover, maybe 3"x5" and a wing nut that holds it on.
Those control knobs are mounted on the control board, there should be two Philips head screws holding the board in. But on my P61 I've never taken that out to get at the fines box.