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Old 22nd Dec 2019, 5:13 pm   #14
peter_scott
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Join Date: May 2003
Location: Edinburgh, UK.
Posts: 2,241
Default Re: JVC 3320 Transport Failure

Hi Davy,

Thanks for your thoughts.

I did remove the drum flywheel and it had the two magnets securely in place. I also ensured that when I refitted it that it was as far up and close to the sensor as it would go.

Although I started the thread explaining that my more modern VHS machine gave ghosting, the reason for the thread was so that I could revive my old JVC that has lived in my attic for more than 20 years so that I could play 405 tapes without ghosting.

All my testing on the JVC has been on a commercially recorded VHS 625 line tape. That said I did try a 405 line tape but of course it just displayed the same fault because the drum was still triggering the sensor at 22.8 Hz.

The sensor signal looks correct apart from the frequency and it is allowing generation of head switching pulses.

The JVC was put into storage in working order and I can't see any mechanical fault. I did replace the drum motor belt although it didn't need it and made no difference. The motor and drum rotate freely and removing the back tension makes no difference.

I think the most likely cause is a faulty capacitor in the drum servo loop. I don't think the servo IC is likely to have deteriorated with age but stranger things have happened.

Peter
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