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  #1  
01-19-2020, 05:20 AM
dima dima is offline
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What causes this noise ?

It's about noise like this:
- https://as1.ftcdn.net/jpg/03/07/88/6...6DPqgYrRN1.jpg *,
- http://www.digiommel.fi/Video%20Sign...log%20VCRs.pdf (Page: 3, description: "Increased tape tension reduces dropouts"** and picture on the left).

* I mean noise something like on this image: thin horizontal white lines, but I mean even longer lines, equally thin, and running across the entire width of the image(but not all and not always, because I also mean short lines that don't run across the entire width of the image and also thick lines, bars something like from the second from the top link to the document given in this post by me - in this document in: Page: 3, description: "Increased tape tension reduces dropouts" and picture on the left), sometimes with very few of them per frame, and sometimes with more.

** From what is written here, it seems that increasing the tape tension can help.
How to do it ?
Is it enough to use two white holes on the bottom of the VHS cassette to properly stretch the tape(until the lock in the middle jumps to the appropriate mode) or would it be a short-term action - for a short section of tape ? Maybe should stretch it by dismantling(unscrewing) the VHS cassette and manually stretching the entire length of the tape around the spool ? Or is it set somewhere in the VCR ?

What filter of those available through VirtualDub would be the best for this type of noise ?

Last edited by dima; 01-19-2020 at 05:56 AM.
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  #2  
01-20-2020, 05:15 AM
msgohan msgohan is offline
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The document you linked already says what causes dropouts. For example:

Quote:
Dropout compensator basics
Dropout compensators are employed to conceal the horizontal white or black streaks that would otherwise be registered in the demodulated video signal. The DOC function is based on the fact that most DOs are random and do not reappear at the same spatial position in the image. Tape DOs tend to increase in number with the age, as a result of chemical deterioration and sub-optimal storage conditions. As pointed out, a DOC cannot completely remove DOs because the circuit has to act on a real-time basis, and without prior warning of impending DOs.
Here is another reference for you. (Digital Video Camerawork by Peter Ward)
Quote:
The correct head-to-tape contact is not always maintained due to tape imperfections or a build-up of tape coating or inconsistent tape tension.
Regarding increasing tension to improve head-to-tape contact: according to my interpretation of this article, this method has only been used for creased / wrinkled tapes. Possibly scratched tapes, but this is unclear from the way the paragraph is written.*

Quote:
Increased tape tension reduces dropouts
It is not uncommon to encounter video tapes with longitudinal creases or scratches. Video heads, traveling across such ridges or crevices by wrinkled tape, cause momentary losses of head-to-tape contact. The contact is often lost immediately before and after the actual defect. However, in such cases, it is usually possible to regain head-to-tape contact to remove screen-wide DOs by increasing the tape tension around video head cylinder (Fig. 4).
...
Figure 4. A VCR head loss of contact at tape creases may be removed by increasing tape tension around the video head cylinder.
* What I mean is that Mr. Backman initially mentions the example of scratches as "not uncommon" but then all later mentions in this paragraph and the associated figure refer only to the case of creases / wrinkles; a separate phenomenon. The only other use of the word "scratch" in the document is "Test tape 3 was made to simulate larger creases or scratches on the tape."

Increasing the tension is a player adjustment, not a tape adjustment: http://www.macievideo.com/VideoHdEval.html

As for restoration of an existing capture using VirtualDub, that may be best asked in a new thread in the Restoration forum; using the correct terminology in the subject line. Here is an example of restoration via Avisynth: Encoding x264/MKV, bad playback near end of title?

Meanwhile, some interesting reading I found while trying to do a search for you:
  1. One-inch Type C videotape characteristics and simulating them (Doom9 forum)
  2. post mentioning creases

Last edited by msgohan; 01-20-2020 at 05:52 AM.
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  #3  
01-20-2020, 09:04 AM
dpalomaki dpalomaki is offline
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The JPG is typical of images shown in VCR manuals as a symptom of contaminated heads. See the attached image from a Sony user guide. (It might also indicate wornout heads.)

Drop out compensation generally involves a player that buffers a frame or field before output, and if a drop out is detected it substitutes an adjacent line for the line containing the dropout.

You should consult the service manual for the VCR to determine how to adjust/set the tape tension. This usually requires special tension measuring tools. Improper tape tension can result is excessive head and tape wear and may cause other playback anomalies. (However going above the manufacturers spec might provide a temporary benefit as deposits shift or are read through due to changed tape pressure.)


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File Type: jpg ContaminatedHeads.jpg (50.8 KB, 18 downloads)
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  #4  
01-20-2020, 11:22 AM
dima dima is offline
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Thank you for your answers.

Everything is fine with the video heads in VCR.

So maybe someone knows "from the head"(has it in his mind) how to increase the tape tension around the video head cylinder in VCR: Panasonic NV-HS1000 ?
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01-20-2020, 12:52 PM
dpalomaki dpalomaki is offline
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Tape tension is controlled by a tension band. The AG-1980 Service Manual calls for replacement every 2000 hours, (same hours as upper cylinder replacement).

The attached figures are for the K Mechanism. Mfgr spec. (for the AG-1970) is 22.5-27.5 gm tension.

This information is provided, but you use it at your own risk. I have no way toa ssess hether or not you have the technician skills necessary to use it propertly. It may not apply to your maching, so you should get the service manual for it.


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File Type: jpg Tension0.jpg (96.7 KB, 21 downloads)
File Type: jpg Tension1.JPG (86.4 KB, 11 downloads)
File Type: jpg Tension2.JPG (67.5 KB, 17 downloads)
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  #6  
01-22-2020, 11:00 AM
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My first inclination would be damaged/bad heads. Do all tapes play this way?

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01-22-2020, 03:28 PM
dima dima is offline
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Is it possible to see in a more practical way, "live" - during playback, see if increasing the tension of the tape causes changes in the image(without direct impact and changing parameters in the tension mechanism in VCR) ?

For example, by pressing the tape during playback in the right place...
Would it give something(when we assume that increasing the belt tension will improve and that this is somehow a solution to the "problem" - or maybe it is necessary to see it must be mechanical adjustment of the tension in VCR mechanism ?) ?
Where would this be best done(VCR space during tape playback) ?
It would be best to do it from the inside of the tape and pressing it with a cotton bud... ?

Or maybe there is another way, an idea for it(what I wrote in the first paragraph of this post asking) ?

Last edited by dima; 01-22-2020 at 03:40 PM.
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  #8  
01-22-2020, 03:57 PM
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Slowly tweaking/rotating the guides, but you may need to dremel your own special tool (start with flathead screwdriver). Be extremely careful, one slip up and you could bork the heads, rip the tape, etc. This is a delicate process without scopes. Even with scopes, not the easiest for a novice.

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01-22-2020, 06:40 PM
hodgey hodgey is offline
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Quote:
Originally Posted by dima View Post
Is it possible to see in a more practical way, "live" - during playback, see if increasing the tension of the tape causes changes in the image(without direct impact and changing parameters in the tension mechanism in VCR) ?
You can carefully push on the tension spring arm (the one mentioned in the previous post) when a tape is playing, though I don't know if tape tension is really the issue here. I would suggest posting a clip showing what issue you get as there can be several things that can cause white stripes/dropouts like this.

My own (and others here on the forums) NV-HS1000 VCRs have issues with compensating well for dropouts compared to other VCRs, maybe yours has that issue as well. I haven't gotten to the bottom of it, but I did discover today that one of the capacitors on the head amplifier board on ours measured bad on my ESR meter, and it also looked like the other one of the same type had been replaced at one point as it was an ELNA-brand cap. Will try to replace the bad one at some point to see if it helps.

Last edited by hodgey; 01-22-2020 at 07:05 PM.
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  #10  
01-23-2020, 03:22 AM
dima dima is offline
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Quote:
Originally Posted by lordsmurf View Post
Slowly tweaking/rotating the guides
What guides do you mean ? Can you explain it to me, show it in the pictures(I'm asking for my certainty) ? You mean these two white roller guides ?
If so, I don't know what you mean(I don't understand what exactly should be done). What should I do when playing with these rollers guides... ?

Quote:
Originally Posted by hodgey View Post
You can carefully push on the tension spring arm (the one mentioned in the previous post) when a tape is playing
You mean this:
- http://www.digitalfaq.com/forum/atta...al-tension2jpg or
- http://www.digitalfaq.com/forum/atta...al-tension0jpg (Tension Arm U), [http://www.repairfaq.org/REPAIR/vcrxprt.gif (Back Tension Arm)], [http://repairfaq.cis.upenn.edu/sam/vcrmprbs.gif (Back Tension Lever)] ?

Because to get to the first one mentioned by me in this post during playback is "normal" impossible from what I checked(I might be wrong). The second has easy access that can be "controlled" by pushing it or pulling it away from the tape - this second touches tape from its inside.
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  #11  
01-23-2020, 10:58 AM
dpalomaki dpalomaki is offline
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I suggest you get the service manual for your VCR and ask questions with reference to images from it, not images that may be for a different mechanism.
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  #12  
01-23-2020, 05:01 PM
hodgey hodgey is offline
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The one in the schematic called Tension arm U.
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  #13  
01-24-2020, 10:02 AM
dima dima is offline
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Quote:
Originally Posted by hodgey View Post
My own (and others here on the forums) NV-HS1000 VCRs have issues with compensating well for dropouts compared to other VCRs, maybe yours has that issue as well.
And how does it manifest itself ? The occurrence of such artifacts about which I write in this thread ? This appears especially on this VCR when playing some "weak", old, damaged VHS tapes or is it different ?
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