Sony DD series (direct drive) walkmans are very popular among portable cassette players because of their high quality construction, excellent fully analog sound quality - and great timeless design.
Although they’re well built, they will not work within specs without proper service. Because they’re 30+ years old, most of them will have some common issues by now.
In this manual I will give very detailed step-by-step instructions on how to fix all common problems - and recommendations on maintenance tasks to do, to avoid future problems. With the help of this manual you should be able to do proper service on any DD unit. I’ve fixed more than 200 DD units and will present my know-how and best practices, discovered through the years. I will try to make it as complete as possible.