The multi-disc CD players are called "changers," because they change the CDs mechanically, allowing CDs to play back to back. Sometimes, these players can act up. If they do, they will usually show an error code. Error code 3 means a mechanical error concerning the laser lens and around the lens, which can be fixed through troubleshooting.
Remove the player's screws with the appropriate screwdriver. Remove all accumulated debris and dust that might have collected in the player causing the mechanism to fail. You can get rid of this by spraying the inside of the player with a can of compressed air.
Soak a cotton swab with isopropyl alcohol and wipe the CD player laser eye until it is free of grime. Grime on the lens can cause the CD to lock up by not being able to read the disc properly. Or, as another viable option, insert a CD lens-cleaning disc into the player and press "Play." This disc will wipe the lens clean.
Inspect the player's fuse. If it is blown, the glass will be covered with a white film and the filament will be severed. A blown fuse can cause an Error 3 because it will stall the player. Purchase a compatible fuse in a retail hardware chain and replace the fuse.
Ensure that the gears are fully lubricated. If not, lubricate with WD40 spray oil. If you see gear belts off of the gears, reattach them.
Reattach the player by putting the screws back in with the screwdriver. Test the player by inserting several CDs in the player and allowing them to change. If they play and change without issue, the error code should be fixed.