JVC HR-S7800U has tearing at bottom 16 lines of image

[iamspuzzum]

Bought a used JVC HR-S7800U locally last year, and have only just begun to use it for transfering. Although the picture looked fine on the seller's tv, I've since found that the bottom 16 lines of resolution (measured in vdub null transform) are misaligned or something. My first guess is the pinch roller needs replacing, but just want to make sure it's not a head replacement instead. I cleaned the roller quite thoroughly, but hardly made a difference. Picture's fine otherwise.. just the tearing at the bottom edge.

Any ideas?

[jagabo]

That's sounds like normal head switching noise. All VHS tapes/decks have it. 16 lines is a little more than usual but not out of the question. You don't see it on TV because TVs hide the edges of the frame -- for exactly this type of problem. See "overscan".

http://preservation.bavc.org/artifactatlas/index.php/Head_Switching_Noise

[iamspuzzum]

Thanks jagabo

I thought it might have been more of a tape curling than the tracking lines. I've never seen a picture with that much tearing. 2 or so lines yes.. but not 16.

I'm going to get it tuned up anyways as I'm sure it's been a while, but just wanted to make sure it wasn't the heads before the guy tries telling me it is.. and proceeds to gouge me.


Even with a cleaning, it does improve somewhat.. so was hoping a new "softer" pinch wheel was the answer. Googling says they should be replaced every 4 years anyways. I did notice the roller looks slightly bevelled at the bottom.. though that might just be my eyes.

[Vidd]

I have the same exact thing with my JVC. But the same tape plays with no issue on my Panasonic (Perhaps 2 to 4 line max). When using the JVC, I usually crop it out with AviSynth and then add a black border.

[iamspuzzum]

DigitalFaq has a similar thread.. with an even worse picture. Suggested possibly an alignment issue.

www.digitalfaq.com/forum/home-video/3032-jvc-vcr-interesting.html

I did read that the alignment of the tape transport needs adjusting every few years.. regardless of use. Seems gravity can set them out of alignment all on it's own.


Feeling a bit better now.. thought I got scammed by the seller, and needed a head replacement. That would'a been expensive.

Still plan on a tune-up servicing though.. new rollers, new belts, timing checked and adjusted, alignments checked and adjusted, all springs checked, and a general cleaning/lubricating as needed. Tune-up kits are cheap.. but I'd rather leave it to a tech.

[JVRaines]

Also, if you're working with a dubbed or edited tape, some of that switching noise may be the actual picture recorded from the source deck. I see this all the time in U-matic cassettes.

[LightWeightProducer]

Older VCRs founded around more analogue principles usually have a trimpot buried somewhere inside to adjust the head switch point. The later ones where more and more digital principles started to creep in usually have no adjustment at all (ie, its all automatic) or occasionally a hidden configuration menu to let a service dept tweak it.

Having said that there's not a lot wrong with the example shown. Moving the switch point much further along is likely to induce issues with vertical sync.

[jefftheripper]

I used to service VCR's of several formats (VHS, Betamax, U-Matic, etc) and what you are seeing is a tape tension problem. Usually the head switching is set 4-6 lines before the vertical interval and if the originating deck has correct "Back tension" and the tape is played on a deck with similar back tension you might see a little horizontal "dancing" at the switch point. If either deck was considerably out of adjustment you'll see it skew left or right depending if the tension error was too little or too much. So, with that being said, you'll need to find a VHS alignment tape to determine which deck is at fault. I doubt you'll be able to locate one these days with the decline in tape use. The JVC alignment cassette was around $300 back in the '70's and the gauge to measure and verify the tension (a Tentelometer) was close to $400. What you're setting is the back tension on the supply reel. You'll see a metallic or plastic band with a felt friction pad wrapped around the supply hub. One end of that band is connected to the tension arm which rides against the tape and the other end is anchored. There will be a bias spring attached to the tension arm. That spring should have a movable anchor bracket which allows adjustment for the tension. You might try it 1-2 mm in either direction to correct for excessive skew at the switching point.