Hi mindink, welcome to the forum. Here's a site that you can download the 'operating manual' but unfortunately, it doesn't have the schematics.
http://www.analogrules.com/
Luckily, Bob Schneider has generously provided a link to a jpeg of it in this thread;
http://www.tapeproject.com/smf/index.php/topic,740.0.html
Have you pulled the boards and cleaned the contacts? Also the all the switches and pots will probably a need cleaning.
I have tried downloading that manual, but after it downloads I get a "windows cannot open this file" error. Is there a trick to opening this file after it has been saved to my computer? Or is there a better source to download a manual for an 8 Track 50/50?
Thank You