This is a Bose Wave Music System Multi-CD Changer Accessory being sold as "for parts or repair". When plugged in, the 3 lights pulse on and off as they should and you can hear the system's mechanics working. If you add a disc to any slot the light turns on (for the corresponding slot), Bose Wave reads "Reading Disc" but then shows "Disc Error" after it's unable to read and the system ejects the disc. Disc trays 3 & 4 WHERE working last week and I took it apart to see if there was any glaring issue as to why tray 2 was giving an error message. I didn't see anything obvious so I put it back together, but after that all disc trays gave the same "Disc Error" message.