I have no idea how much of the company is left, if any, but used to be long ago you could call Tandy and they would send it out. usually the owner manual included schematic on last page. If that doesn't work, and Elektrotanya doesn't have it, yep you are truly lost at sea. Tandy sold out long ago, but Radio Shack still exists. We could always ask them.
Although it looks like we could trace that one out without getting a head ache.