Also, do a search on eBay for "Sencore PA81". When you get the results page, scroll down and on the left and click on "Sold listings".
A few listings down (probably you at the top
) is a seller with a listing for "14 Sencore Manuals, 6 Catalogs on CD - SG165, SG80, PA81, TF40 manuals schematic"
In the listing description it reads "PA- 81 Stereo Amp Analyzer – Instruction Manual "Operation, Application and Maintenance", Schematic and Parts List + the Application / Training Notes - "Sencore Tech-Tips - #179" - "Learning to Use the PA-81" (BOTH ARE HARD TO FIND)".
He sold what he had, but you can do a "Contact the seller" via his eBay page. He might be able to create a new one for you.
For $12.99 it's worth a shot.
T