You can find the manual for an 8500/B online, the only difference in the 8500 and the 9000 is the display, 8500 is analog while the 9000 is LCD. (I may even have the downloaded version, I would have to dig around to see??)
The 9000 and the 8500 were top of the line machines in their day, actually a few years ahead of their time.
They are four filter fast sweep machines,
They ID better than most modern detectors, plus they ID as deep as they detect.
They are heavy,
The hip mounted versions was the more desired.
The 9000 suffered LCD display problems in that they would lose their detail (bleed) they're is NO replacements displays for these in the world other than used.
All the Teknetics models of that era are known to have battery contact problems.
The new Teknetics company isn't really related to the older Teknetics company other than the rights to the name. So the current Teknetics offers NO support for the older units.
For service, it would be Keith Wills at brokendetectors.com When the old company went under Keith bought ALL the remaining Teknetics factory assembly line stock. So, some parts are still available (the LCD displays have been gone for years)
The most common problem was the battery contact clips, at last check Keith still had those and they are supposed to be a little better made clip (battery contact)
Many times coils and parts units come across fleabay.
Mark