Arno,
I used one of those both at JPL and Caltech in the '70s. Worked quite well.
I don't have any service information but I did scan the user manual
that I have. Al or others may have other scans or additional
information. For my scan, see:
<http://dundas-mac.caltech.edu/~dundas/retro/DEC%20Docs/Tektronix/070-1404-00.pdf>
John