Justin
A J Tannenbaum co. sell manuals, etc. for a myriad of vintage test equipment. The operators manual (which USUALLY includes a schematic) is available for your 589A for $17. I have purchased from them before and was satisfied. Your tester is listed on the following page http://www.agtannenbaum.com/s_cat.html#supreme and their home page is http://www.agtannenbaum.com/
Dennis Wess