What does a cassette capstan do and what causes tapes to play fast?

Short video explaining how a capstan works in an audio compact cassette player.
If you have a cassette player with a playback speed that is two fast, the cause is usually down to a bad capstan pinch roller.
If the pinch roller is slipping due to a contaminated surface, it can be cleaned up with some isopropyl alcohol and a cotton bud.
Cassette deck shown in the video is a Sony TC-FX20.
Hopefully this will be helpful if you have a cassette deck repair where speed is the issue.
The principle is exactly the same on reel to reel tape recorders, just on a larger scale.
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