Recently my girlfriend got a call from a marketing firm asking if she’d be interested in watching a videotape of a potential new television show and giving her reaction. She agreed, and they sent her the tape. After she watched it they called back to get her opinion (although, it turned out they wanted to know what she thought of the COMMERCIALS more than the show, but that’s another thread).
Anyway, at the end of the phone call they told her she could just throw away the tape, as she wouldn’t be able to watch it again. Sure enough when she tried to watch it again she couldn’t!
The only way I can think of that it can be ones is to have the tape break. If the end of the tape is specially made to break away and the trailing leader is opaque, so the end-of-tape sensor in the VCR can’t read through it, then when the tape reaches the end, it simply snaps off the reel. If you still have it, lift up the front cover by pressing in the little square button found on the right side with a small screwdriver or pen while lifting the door upwards. You’ll know if the tape is intact or not. If you want to watch it again, a little Scotch tape wors wonders for tape splicing. Most cassettes come apart by removing four screws.
Well, perhaps there were no “teeth” inside one of the spool cores. That way the VCR could only drive the tape in one direction – that is in the PLAY direction. When she tried to rewind, the capstan that spins the spool in the other direction could not engage the toothless spool core.
Or the spool that the tape wound onto had a low powered magnet in it that effectively wipes the tape as it arrives. Or tiny spikes on the spool that punctured the tape.
I can think of a few methods that might work. But nothing as cool as a self-destructing one involving whisps of smoke like Mission Impossible.
No, those teeth are to engage the reel lock inside the cassette, the purpose of which is to prevent the reels from turning when the tape is in transit, causing slack which can lead to jams. Although I can envision a sort of one-way device installed in the cassette to do the same thing you suggest. I’d bet the cassette shell is glued together to prevent casual tampering, too.
QED, I don’t think you are understanding me. I know the teeth on the outer rim of the “spool core platter” (I just made up the term, but it works) keep the spools from turning in transit. But that is not what I’m talking about.
Look at the bottom side of a VHS tape. Inside the two spool cores are teeth. The VCR capstans (which have teeth too) engage the spool cores so the VCR can drive the tape in either direction. Remove the teeth from inside a spool core and the capstan can’t engage it; if it can’t engage it, it can’t spin it.
Another possibility would be a sprung blade, angled like the blade of a woodworking plane so that the tape slips over it harmlessly in one direction, but is cut through if you try to rewind.
Or some sort of sprung mechanism that locks into a hole in the spool - the hole being exposed by the tape running off it.
I suspect though, that stuyguy nailed it with the missing teeth thing.
They used to do this with advance-screening videotapes. There was a counter embedded in the tape that counted the number of times that the movie was watched beginning to end. When that counter reached, say, three, the tape no longer worked - I think it couldn’t be rewound.
It seems to be an technology that was originally supposed to replace rental videotapes. The idea being you rent a video, watch it once, and it self-erases. Thus no late charges. The idea didn’t take off, though.
There also seems to be self-erasing DVDs out there that erase themselves 24 hours or so after being removed from packaging. They are made by a company called Flexplay. Their site isn’t very forthcoming with the technology, and doesn’t mention if they used to make the videocassettes.
I would love to take this tape apart. Could you provide some more info for us Hokienautic? I think the magnet erasing is the best idea (among other good ideas). Try a compass moving around the tape. Does one end of the compass like to point to a specific spot at the front of the takeup reel side?
If someone sent one of these to me, I’d have it apart before watching it the first time…
Unfortunately I don’t have access to the tape for further information, as my girlfriend lives in another state.
She did rewind the tape and try watching it again, getting blank tape. When I asked her she told me it at least looked like the tape had been rewound to the start – my initial thought was they had some sort of blocking tool that once the tape went past that spot it couldn’t rewind before it.
It’s probably a magnet then. I doubt if it’s a permanent magnet though, since even a strong one is insufficient to wipe the signal completely in one pass. I’d bet there is a small battery-powered circuit inside to efficiently erase the tape with an alternating magnetic field, the way normal erase heads do. I’d love to get my hands on one of these too. Anyone know of a way to request one and from where?
A magnet is the answer. I participated in an identical survey a couple of years ago (the tape was a pilot for a dreadful sitcom called “Dads” featuring Rue McClanahan that fortunately never saw the light of day). After watching the tape, I opened it up and found a small but unusually powerful magnet held inside with black electrical tape, right where the tape passes on it’s way to the takeup reel. The tape and cassette itself was otherwise ordinary in every way. I removed it and was able to use the tape normally (planned on recording on it but the tape was only a half hour long). If I had known that’s what erased the tape, I would have taken it out beforehand. I still have the magnet (on the refrigerator) and the tape. I can post more information about it later tonight after work, if anyone’s interested.
BTW, forget about all of the free product samples they say they will send to your girlfriend for her trouble. We never received ours.