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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 12th May 2021, 8:34 pm   #21
hillsrob
Tetrode
 
Join Date: Apr 2021
Location: Wimbledon, London, UK.
Posts: 56
Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by andypilgrim View Post
If you have noise at both the top and bottom of the picture it suggests that the head to tape contact is poor at the beginning and end of the wrap, this was often caused by low tape back-tension. The back tension is provided by a brake band around the base of the supply spool and the tension is controlled by a guide lever /post that is on the left of the mechanism normally between the first fixed guide as the tape comes out of the cassette and the erase head. Two possibilities, one is that the pivot for that guide lever is gummed up so the guide is not free to move, the other is that the felt lining has fallen off the brake band, both possibilities are equally likely.

I would say twiddling with the entry and exit guides on the drum is a bad idea as the don't tend to go out of adjustment without some human help and re-aligning them requires an oscilloscope and ideally a proper alignment tape to get the envelope flat. As someone has already said, the adjustments affect each other and you cannot really gauge what is happening from a picture alone.
Thanks for you advice andypilgrim. That machine is now working pretty well with only minor tweaks of the input and output rollers. I have been able to buy the complete JVC tool set on Ebay and have also bought a decent used Tektronix scope. I'm looking out for an alignment tape. (I have a Sony Betamax one I bought in the 70s)

My attention has now turned to a rather sick JVC HR-3330. The subject of another thread. https://www.vintage-radio.net/forum/...d.php?t=179353
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Old 12th May 2021, 10:42 pm   #22
nickdoofah
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Join Date: Jan 2009
Location: Littlehampton, West Sussex, UK.
Posts: 142
Default Re: VHS Tape Path Alignment

Quote:
Originally Posted by andypilgrim View Post
If you have noise at both the top and bottom of the picture it suggests that the head to tape contact is poor at the beginning and end of the wrap, this was often caused by low tape back-tension. The back tension is provided by a brake band around the base of the supply spool and the tension is controlled by a guide lever /post that is on the left of the mechanism normally between the first fixed guide as the tape comes out of the cassette and the erase head. Two possibilities, one is that the pivot for that guide lever is gummed up so the guide is not free to move, the other is that the felt lining has fallen off the brake band, both possibilities are equally likely.

I would say twiddling with the entry and exit guides on the drum is a bad idea as the don't tend to go out of adjustment without some human help and re-aligning them requires an oscilloscope and ideally a proper alignment tape to get the envelope flat. As someone has already said, the adjustments affect each other and you cannot really gauge what is happening from a picture alone.
The JVC 800 900 Series & some SVHS decks from the early to mid 90's were notorious for the guides working loose on both entry & exit sides, causing major problems! I always thought it was a shame as many machines were simply scrapped or dumped (Certainly here in Sussex) as owners were told the 'heads were gone' etc! Realigning was easy enough in reality of course, the HiFi machines being a little more critical before behaving again & once the tiny allen screws were pinched up nice & tight these machs seemed to last! The tiny smd cap on the lower drum would fail too causing the drum to run up to crazy speed right before your eyes! Happy days..........
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