Sony TC-K611S cassette deck : Belts - Speed - Bias

Repair video showing me service this impressive 3 head, 3 motor cassette deck from 1993.
Replacing and fitting rubber drive belts. Changing these as the fitted belts have turned to a sticky goop over the 30 years.
Also adjusting the capstan motor speed using a test tone calibration tape and oscilloscope.
Tape Bias set and explained.
Finally a test recording using a TDK MA90 metal type IV tape (the tape used in the video was very worn and bias levels needed to be adjusted quite a lot. I have since tested with a new type IV tape and the adjustment required was only slight)
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