Siemens RW 721 is the clone of Sanyo CP 10. Grundisg CDP 50 is a same modell. Citizen CDP-120 is a clone! Is it true, is this modell Sony D50? http://discman.c1.biz/siemens.html
SONY D50 is quite similar with the CP10 but totally different design if you open their back covers you'll confirm it. However, most of the components and modules are same like power box.
These are so rare, each and every one still in existence must be fixed!
What is wrong with it? post some photos, since I overhauled its "clone" Loewe maybe I will be able to suggest something useful