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I had a few people comment on my YouTube video where I was demonstrating the problem. Thanks go to @Phil-d2i6s, @SUMI, and @vvm2004. So for posterity's sake, here is a compilation of explanations of the issue and how to resolve it for anyone else who may be having the same issue as I did with my JVC:
The problem is caused by the carbon brush and the ring inside the motor being oxidized, in addition, the noise reduction capacitors are aging, causing noise pulses when operating. The reel motor generates electrical commutator noise: not too much during play and search modes when the supply voltage (and current) to the motor is lower, but much more during the high speed winding modes.
In addition to the motors being electrically noisy, the tape end sensor circuits are potentially too sensitive and are only just turned off while the tape is interrupting the IR from the LED. The electrical noise from the motor is seen and amplified by the end-stop phototransistors resulting in negative-going spikes that make the controller think the end of the tape has been reached.
The correct method for repair is to service or replace the motor, and to replace the noise reduction capacitors. However, this may not always work. So in addition to motor repair and recap, adding 100 uF capacitors to the motor and both end-stop sensors may finally resolve the issue.
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