Friday, June 29, 2012

Demagnitizing Camcorders

My SONY DSR-PD150 is over a decade old, but I still use it, because it's good in low light and very reliable.

Unfortunately I recently threw it into the back of a car full of big self-powered speakers, and it became magnetized. Perhaps the cause was direct contact with the speakers' magnets, or perhaps moving through their magnetic fields, or perhaps from some kind of reverse "Faraday Cage" effect (magnets inside a Faraday Cage, which usually protects from electric effects outside the cage, but, who knows, might amplify the effects when magnets are inside the cage).

The previously reliable image and sound recordings became spotted with dropouts, digital noise, etc. Definitely magnetized heads.

So, how to demagnetize a camcorder? Is it possible?

Yes, it is possible.

I'll say what worked, and then reconstruct the discovery process.

The solution is:

1) get new tapes
2) with each tape:
3) record once for the length of the tape
4) play back once for the length of the tape
5) throw away the tape
6) repeat 3-5 with new tapes until the magnetizing goes away


This sounds unlikely, I know. Like many things related to magnetism, our intuition fails us. Mine did.

At first I tried two different miniDV cleaning tapes. They were no help. These tapes might be helpful in other situations, but apparently not with magnetized heads or magnetic particles, which I imagine were magnetically attached to the heads. I also tried just recording and playing back on the same miniDv video tape, over and over again: this also did not help.

I found one intriguing post, here, and decided to use it as the basis of a little theory, and think through the likely repercussions. If it's true that the use of a camcorder tends to neutralize, rather than magnetize, the recording and playback heads, then we would need to optimize the conditions under which the camcorder could eliminate the magnetic particles depositing on its heads. The only thing that could do this is the tape, since, being magnetic tape, it is both the source of the particles and a potential mop of them. So, after having tried so many things to no avail, I simply broke out a new tape, recorded the full 40 minutes (DVCAM mode, but it wouldn't matter what the tape format is) and played it back. Still dropouts. But it seems a little better. I threw away the tape, broke out a new one, and did the same thing. On the playback, it seemed like there were markedly fewer dropouts. I threw it out. One more time, and this time, the playback was flawless.

Apparently I'd used the new tapes as "clean magnetic mops" to pull tape particles, and their attending magnetic charge, off of the camcorder head. It takes a certain leap of faith to throw away brand new camcorder tapes, but that seemed to be the only answer. I know from previous experience that demagnetizers are tricky and can make matters much worse. Throwing away a few new tapes is well worth it, since it can refurbish a camcorder.

This previously highly-magnetized piece of equipment had demagnetized itself, tending towards neutral, given neutral tapes to help it along with the clean-up. I don't guarantee it, of course, but, for me, the effectiveness of this technique spoke for itself.