Not working error 50 and 70

Clean the unit if possible. does the cartridge eject? if so, load it with a cd player cleaner, preferrably one that uses a cleaning solution. put it in tray slot 1. load and wait. try this a few times then try a good disc, one that is not scratched up. changers are hard on cd's. If it's still not working, below the cartridge slot there should be an inverted dimple that you can press with a ball point pen. This is a reset. It should have this button, I just can't remember the exact location if it's not right there. Hope this helps. If you have a spare cartridge try that as well, as they warp.