'70's Morley Wah Volume question

I have one of the old Morleys that I want to resurrect. I bought it new many eons ago. It's the old chrome style with an AC power cord. The sweep of the pedal is detected by a photo sensor that picks up light from an internal bulb.
Does anybody have any experience in calibrating or adjusting the sweep of the pedal?
At this point, rather than going "WAH" when rotating from back to front, it's more like "OWOW". In other words, it seems to be starting and ending at the wrong place.

Thanks in advance!

I believe as you move the pedal up and down, it allows the light to shine on a light sensitive resistor, there should be a tapered hole in the blocking material.
Here is Morley’s web page.
http://www.morleypedals.com/downloads2.html
Here is another forum discussing the same problem.
http://acapella.harmony-central.com/archive/index.php/t-1459466.html
The Morley page has links to the owner’s manual, and schematics.

Thanks for the info!
I'll give it a closer look see tonight!