Before you buy a service manual for your Tektronix oscilloscope or HP signal generator, you should take a minute to search for the several manual repositories that provide these service manuals for free.  Manuals are typically available as Acrobat (.pdf) files, some are available as .djvu. You may not always be happy with the quality of the manual, but even a poorly scanned manual should get you started on repairing or calibrating your trusty favorite.  Ebay prohibits providing direct links in guides or reviews, so here are some hints that should allow you to locate the most popular online manual repositories.  Try these:  "boatanchor manual" "free manual links" "digitized manual collection" "Tektronix manoman".  Good Luck!