Finding pinout of a servo encoder?

Building an XY stage with Buhler 1.13.043 servos salvaged from an old HP ink jet plotter. Documentation is nil. The encoders have 5 pins. There are two rows of holes on the disk, one coarse and the other fine, so I asume there are two sensors. How would you go about figuring out the pinout without doing any damage?

I am thinking that if I can find which pins go to the LED I can use the 'scope to figure out the output. I am reading 32 meg between pins 1 (+) and