Cassette tapes are essentially a magnetic tape that is wound around a pair of reels and placed inside a plastic case. The case protects the magnetic tape and allows the reels to turn freely when played through a tape machine. Most often, the tape becomes the culprit when a cassette is broken, as the plastic casing remains static and has no bearing on how the tape inside turns or plays. But if a problem develops inside the case, the case will have to be opened to fix the issue.
Determine the problem with the cassette tape. Bunched-up tape, bound-up tape or foreign objects will not allow a tape to run properly in the tape machine. In every one of these scenarios, for a proper repair the case will have to be taken apart.
Locate the screws holding your cassette together and remove them. They are tiny, and a jeweller's screwdriver works the best. Glued-together plastic cases can be opened up by using a hobby knife to cut along the edges on the plastic case at the seam where they are joined. Start at the front at the opening of the cassette, and run the blade along the entire seam.
Remove the cover of the cassette and inspect the problem. Any foreign object inside the plastic case must be removed. Bunched-up or folded tape can be gently straightened out and carefully rewound back onto the reel. Bound-up tape can be released from any area where it is "pinched" and won't move.
Replace the cover when the winding problem has been solved. A good way to check that everything is working is to wrap a few pieces of cellophane tape around the eraser of a pencil, then insert that end into a reel. Hold the tape closed with your fingers and slowly wind the tape using the pencil as a drive mechanism. If it winds easily, the problem is solved, and the case can be glued together by dabbing a little plastic glue on the edges of the cassette to join the two halves back together.
Rewind a bumpy-looking tape to the end and then immediately fast-forward it once again to the end. This action will restack a bumpy tape on the inner reels, which will allow it to play normally.
Pull the two ends out of the cassette case. Any wrinkles, bending or folding on either side needs to be cut off with your hobby knife.
Cut the tape neatly on both sides with a hobby knife for a good splice. The best way to do this is to slightly overlap the two exposed ends and cut down the centre.
Splice the tape together using either a bit of cellophane tape or a commercially made splicing tape. A good rule of thumb here is that if you intend to play the tape over and over, use a commercial brand of splicing tape. It can be found at any electronics store. If you just want to play the tape once through to make a copy, a piece of regular cellophane tape will do the trick.
Tape the splice together. When using cellophane tape, always tape it on the back side so as not to affect sound quality. Trim either splicing medium precisely with a hobby knife to the width of the original tape. This will ensure that the tape winds properly on the reels, and also ensures the least amount of playback degradation.