Which passthrough devices straighten out the bottom of VHS signals?

[Brad]

You could using your vcrs tracking adjustment.

Meant to respond to this back when it was posted. I tried adjusting tracking on a VCR with several lines of distortion. Only about 2 were recovered.

(I neglected to convert the sample from TFF to BFF when I encoded it to DV for upload; oh well.)

[smrpix]

..

[Brad]

Does ".." mean something?

[smrpix]

Does ".." mean something?

It means I deleted my comment because it was redundant and didn't contribute. Nothing more

[MoreQsThanAs]

Realize I'm a Johnny-come-lately here but I appreciate the dialog in this thread. I was always of the impression that in an analog conversion the line at the bottom was the control track of the tape.

What I typically have done is remove the effect of the bottom part of the video by putting a black region box around the area. I think the largest area I've had to remove at the bottom was 17 lines, but as a norm usually 9 or 10 lines.

[magikarp99]

FWIW I've seen one VCR (and I mean one out of maybe 120 I've played with over the years) that put the head switching noise at the top of the active picture. No idea how or why it did this, and it died before I had chance to investigate further. Maybe this was a symptom of it dying.

Do you recall the model or manufacturer?

I remember the service manual specified the head switching to occur at so many lines (can't remember) from the bottom. However, with my TV, I could still see the head switching, so I adjusted it further down so that it was not visible on my TV. I'm guessing if you adjust the head switch too low (like line 1), the picture will become unstable.

Yep, that's what I've read in a couple books. If you place it too low you start affecting VSYNC. JVC managed to do it with the VCR I mentioned above however, and Panasonic as well with a few similar "Professional" behemoth models. What I don't understand is why they referred to this as "masking" since that implies just covering up the problem, even though it does correct it for my camcorder tapes and commercial releases.

The reason they referred to this as masking, is because by default these decks not only pushed the switching noise down but also masked the remaining noise from the image. There is an internal switch on one of the modular video boards which must be flipped to disable this masking.

I remember the service manual specified the head switching to occur at so many lines (can't remember) from the bottom. However, with my TV, I could still see the head switching, so I adjusted it further down so that it was not visible on my TV. I'm guessing if you adjust the head switch too low (like line 1), the picture will become unstable.

This is interesting, it would be good to know how to do this. I wonder how many decks could be improved with minor hacks like this. For example, I have a nice Panasonic pro deck that produces a reasonable image and is exceptional at tracking poor HiFi tracks. The hindrance on the image quality is the analogue noise reduction (it seems to pre-date DNR), the video boards have adjustable pots that I believe could be used to tweak or even disable the filtering, but some are unclear and I haven't had the time to mess with it yet.

[XperienceD]

@vaporeon800:

You own a JVC BR-S525 - does it show the distortion at the bottom? My BR-S522E shows very minimal head switching noise, so I assume that a BR-S525 behaves no different. Or are you interested in eliminating head switching noise of those videos already available (captured with a different VCR)?

[magikarp99]

[Attachment 23233 - Click to enlarge]

The standard placement is apparently during blanking, 6.5 lines (6.5H) above VSYNC. VCR Troubleshooting & Repair notes this on pages 136 and 289.

Standard placement is 6.5H ahead of V-sync in recording
Your JVC has the ability to record at 6.5H, but shift 2H to 4.5H in playback.
It is worth noting that the 822 and 622 models can take this even further and offer the ability to record at 2.25H, and play back at 1.25H for use in closed-circuit systems.

What is interesting is that at least some Panasonic decks don't adhere to the standard, but actually raise the switching point to 7.5H, rather than lower it.

After doing a quick bit of reading, it seems that if anyone wants to lower the switching point on playback in any of their decks this can be done by adjusting the phase generator (PG) shifter. As jimdagys has said, adjusting this beyond the tolerance level of your monitor/capture device may result in vertical jitter, and an unstable image.

[Brad]

You own a JVC BR-S525 - does it show the distortion at the bottom? My BR-S522E shows very minimal head switching noise, so I assume that a BR-S525 behaves no different. Or are you interested in eliminating head switching noise of those videos already available (captured with a different VCR)?

The images in post #47 are a camcorder VHS played on the BR-S525U. But since these "Professional" beasts only play SP mode, they aren't a complete solution.

After doing a quick bit of reading, it seems that if anyone wants to lower the switching point on playback in any of their decks this can be done by adjusting the phase generator (PG) shifter.

I'm guessing that's a bit more involved than turning a knob inside.

[magikarp99]

After doing a quick bit of reading, it seems that if anyone wants to lower the switching point on playback in any of their decks this can be done by adjusting the phase generator (PG) shifter.

I'm guessing that's a bit more involved than turning a knob inside.

Not at all, there will be a PG shifter adjustment pot. If the deck is dual standard, there may be one for both PAL and NTSC. I haven't tried this yet, but theoretically what you would do is play back a tape and slowly adjust the pot until the noise is gone or the video becomes unstable. Note, if you want to bring your deck back to exact factory spec, you will then need an oscilloscope.

This adjustment should be on the servo board, which on pro Panasonic decks requires the removal of the side panel. Note, I am not sure how an advanced deck like the 22 series, that does switching point shifting will react to having this put way out of spec.

Note that I take no responsibility if anyone damages their deck trying to so this. If you aren't confident in what you're doing then don't do it. And if you aren't certain of the function of any internal adjustment, or the adjustment procedure for it specific to your deck, then again, don't do it. Depending on your deck, there may or may not be further tracking adjustments required after altering the switching point.

[magikarp99]

But since these "Professional" beasts only play SP mode, they aren't a complete solution.

Another user made mention to a pro deck that plays back LP tapes. The deck is PAL, but there may be an NTSC version.
https://forum.videohelp.com/threads/363817-Panasonic-ag-5260-%28pal%29-vcr?p=2323567#post2323567

There is a "tear down" here, all of the photos are at some impractical angle though.
http://insidehifi.blogspot.co.uk/2013/03/panasonic-ag-5260.html

[Brad]

That isn't one of the handful of decks that advertise the masking feature, though.

@magikarp99: I have a few regular VCRs I wouldn't mind killing. Would the adjustment be accessible on those?

[magikarp99]

@magikarp99: I have a few regular VCRs I wouldn't mind killing. Would the adjustment be accessible on those?

I can't comment on all VCRs, but this adjustment is accessible on at least some consumer gear. It will be on the servo board, and labelled something along the lines of "PG shifter".

[Quasipal]

Just to add if the tape is a dub from another tape then the switching noise is 'baked in' and cannot be removed.
Tearing below the switch point means the back-tension is too high or low. I have only one VCR - a Panasonic NV-F70 - that shows almost no switching or tearing. By adjusting the switching point pot I moved the switch point right off the picture - but the HiFi sound starts to suffer so I use this for linear sound tapes only. It is possible to do on older VCR's - newer ones are done with a special setup tape in service mode.