Bridgeport Textron DRO

I'm trying to make my swap meet Bridgeport/Textron DRO work (linear
glass scales); maybe someone has an idea.

1) The display lights up and reads 0.0000 on both axes.

2) When I move the read heads on the scales nothing happens, although
once one axis did change to 0.0005 for a few seconds.

3) I can't see any light coming from the read head LED's--but maybe
they're infrared, etc.

4) Maybe the read heads have to be carefully aligned a la the
installation manual in order to do their work? I haven't wanted to
actually install the scales until I knew they worked.

5) The dust strips are off the scales--maybe light contamination is
the problem?

I was able to get the install manual from B'port--but there are no
pinouts or descriptions of what kind of signals the scales should
send to the box or what brand of power the box should supply to the
scales. If someone knows these parameters or has a service manual
gathering dust, let's make a deal.

Thanks very much in advance.

Jack