What causes oscillating VHS tracking error?

[thethirdmancelloveal]

Hello,

I am currently in the process of digitising a PAL VHS from 1998. It isn’t a commercial tape, but it was duplicated by a professional video service back in the day. My setup consists of a JVC BR‑S800E going through a FOR‑A TBC via the S‑VHS connection. The signal is then converted to SDI and recorded with a Blackmagic HyperDeck. All devices are in good condition, and the VHS deck has been recently serviced.

When I play this tape, the tracking level goes from normal to very bad within a 5–10 second period. As a result, the picture changes from stable to glitchy, and sometimes the colour is completely lost. The signal is so poor that my TBC struggles to maintain a stable video signal, and the time counter on the deck is not working.

It's really coming from the tape because otherwisw, my setup works great.

The tape itself seems fine—no shrinkage, no mould, the reels move freely, and there are no unusual noises while it plays.

What could be causing this oscillating loss of tracking signal? Bad storage conditions, a poor‑quality tape stock, or a weak tracking signal that was already present when the tape was duplicated?

Thanl you and kind regards

[lordsmurf]

Welcome.

Typical reasons =
- misaligned recording
- VCR head damage in that mode
- sticky shed syndrome (SSS), tape needs baking and special handling (home DIY will usually ruin gear)

[keaton]

What you describe certainly sounds like the control track on the tape is not aligning with the player. Weak signal on a VHS tape from 1998 due to aging or storage conditions is not what my experience would suggest. I've seen weak signal on 3/4 U-matic tapes of a certain stock from the early 80s. However, that is a completely different tape stock and format. If you had sticky shed, you'd have very dirty heads, and you'd see snow and then complete lack of picture and possible stoppage of tape movement altogether due to severe friction between the tape and tape path. The tape counter not moving is something I have experienced with a VHS or Betamax tape that has a misaligned recording (i.e. control track).

Since the player is good and the tape doesn't show any signs of physical damage along the bottom, then all signs point to a bad transfer on a machine where the A/C head (Linear audio and Control Track) was not well aligned.

Perhaps this wasn't noticed before when viewing on a TV, they did hide a lot of problems on a tape that are now seen in digital capture setups. However, it would surprise me if you don't see an issue when playing it on a TV, because when the tape counter is not moving, it cannot find a control track. Without a control track, the player would not output video.

Assuming a misaligned recording that does have a control track, but not necessarily visible on a properly aligned machine, the only way to possibly recover the tape is to use a different machine that you are OK adjusting the A/C head on until the control track is found on that tape. This is an advanced operation, but there are some threads on the forum on this if you want to give that a try. Of course, you do all of this at your own risk. It shouldn't harm the tape, but the machine would need to be realigned by an experienced person once the transfer is done. Or perhaps you can find someone experienced to do this experiment for you to see if this tape can be played back on an adjusted machine.

-- merged --

Thinking about this some more, perhaps what happened is the tape was placed near something too magnetic, and part of the tape signal has been destroyed. That could explain how the transfer used to be good when first done, but is now in such bad shape.

[radiokom]

JVC BR‑S800E is professional machine (without line TBC) and commonly they all has a lot of wear on heads and transport (tape tension etc.) is out of alignment in many cases. I have some similar Panasonic, on some tapes they works satisfactory, on some not. I do not use them more than 15 years any more, there are recommended consumer SVHS decks what are far better for digitizing. Simply try another VCR and look what happens first.

[thethirdmancelloveal]

Quote:

Originally Posted by keaton

Assuming a misaligned recording that does have a control track, but not necessarily visible on a properly aligned machine, the only way to possibly recover the tape is to use a different machine that you are OK adjusting the A/C head on until the control track is found on that tape. This is an advanced operation, but there are some threads on the forum on this if you want to give that a try. Of course, you do all of this at your own risk. It shouldn't harm the tape, but the machine would need to be realigned by an experienced person once the transfer is done. Or perhaps you can find someone experienced to do this experiment for you to see if this tape can be played back on an adjusted machine.

-- merged --

Thinking about this some more, perhaps what happened is the tape was placed near something too magnetic, and part of the tape signal has been destroyed. That could explain how the transfer used to be good when first done, but is now in such bad shape.

Thank you very much for your answer. That's the next thing i will try. I will play the tape on another machine and adjust the heads. That's an operation i've already done in the past.

Now you last sentence catched my attention because that's a thought i came across yesterday. Maybe the tape was stored next to a loudpseaker or something like that and magnetic properties were partially affected, hence the oscillating tracking level.

I will continue to investigate and keep you all posted. Thanks to everyone who already posted an answer. Much appreciated.

[latreche34]

Sometime a simple cleaning of the AC head fixes the problem.

[thethirdmancelloveal]

Well tonight i tried the tape with my JVC HR-S9500 through the For-A TBC and the tape played without problems. It's odd because the JVC  BR‑S800E (the professional one) usually works better with old tapes. I guess the S9500 is more tolerant to weak control track signals or has better electronics for it. The only thing is that the color saturation is not quite right on this deck. But i can correct that with the TBC using the saturation control or the AGC.

I still would like to know why the control track signal is oscillating regularly like that. I really suspect the tape was stored near a magnet of some sort.

Thanky to everyone who took time to give me an answer.

[keaton]

Glad to hear you resolved things!

Perhaps you had a "thin edge" type of situation where the alignment of the tape with the AC head was just slightly different enough to see a stable control track.

Or maybe it's something else entirely. We don't always get to know why, we just make the best guess we can and try as many things as we can and are grateful when something works.