In my experience lapping the physical wear down of the surface of a magnetic head that touches the tape doesn't happen to cassette heads in the same way it does to the heads for higher speed, higher tension, openreel formats. But they do fail in this video I show how this failure manifests, as well as more tests you can using bits and pieces from your scrap pile to distinguish between faults with the magnetic heads, and other areas of the system.

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TETRAKAN Fix & Use Tape Recorders

Overviews; teardowns; repair vlogs; techniques; tutorials; demo recordings...
...covering every cassette multitrack recorder ever made!*
*(eventually)
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I prefer to answer questions in the youtube comments where my answers can help more than one person, but if you need to share photos etc, you can message me via facebook.
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