Degaussing Questions

In order to completely "erase" magnetic media, it is recommended that you use a degausser. Radio Shack used to sell an inexpensive Audio/Video tape eraser that looks like a black steam iron with a button. As I recall, this is recommended here for degaussing. The end result is a random redistribution of the magnetic particles on the recording medium. Anything previously recorded is deleted and unrecoverable. But I have some questions, and they may be dumb ones, but I want to know some things :

For wound magnetic tape, is the steam iron degausser sufficient? Would the wrapping of the tape shield the inner portions of the tape, i.e. those closer to the spool or reel, from the degaussing effect? Aren't their erasers that run the tape through a machine so there is no question that all areas are properly erased?

For hard drives, can you use the degausser effectively without removing the metal cage covering the platters? Or do you have to touch the platters to the device? Desktop hard drive platters tend to be made of some fairly rigid steel, does the hand-held degausser have the power to randomize the bits?

Floppy disks seem a particularly suitable target for a degausser, as the surface is easily exposed and the covering is very flimsy. Can degaussing make unreliable disks work again? Can you "overdegauss" a disk (or anything else) like overexposing an EPROM to an UV eraser. I know it is not recommended to degauss a CRT too often.

Finally, does degaussing have an effect on nearby electronics? Does it, for example, cause harmful EMP? Will it affect the read/write heads of magnetic disk drives?

Hi
You can not over degauss a tape or floppy as long as the magentic field isn't
strong enough to melt the disk.
It doesn't wear out.
Any strong AC magnetic field can cause heating in anything that
is conducting. It is unlikely to create current sufficient to damage
other electronics. Consider that it has many turns of current
carrying wire to create the magnetic field you are getting.
Your electronic would most likely look like a single turn to
the field. As such, not enough voltage would be created to
do damage. Current without voltage is not usually a problem.
Dwight

It used to be that some floppy duplicators used very high write currents when creating copies. A degausser does help to make those disks more amenable to overwriting.

FWIW, using the steam iron type of degausser involves bringing the disk into contact with it and then slowly moving the disk away in sort of a circular motion.

I never used one first hand but for a while we at work had a requirement from a client to wipe backup tapes with a degausser. Yes it affects nearby electronics/magnetic strips so take off your watch and leave your wallet and other things elsewhere while you play.

Since you degauss tapes (which is what the degaussers are for, after all) along the sides of the reel it's equally effective on the inside or outside.

As to degaussing hard disks, I wouldn't recommend it if you plan to use the disk again; many disks have a platter devoted to servo information without which it becomes a brick.

Definately! I accidentally put a computer speaker on an IDE drive and that killed it immediately. It wasn't running or even plugged in. Just taking up space on the workbench.

Here are some random bits of information:

Degaussers are absolutely mandatory for audio tape. If you reuse tape, you must bring down the background noise if you want to reuse the tape for anything approaching music or professional level recording. The effect is dramatic. The erase heads are far from adequate for this purpose. All studios used to have them and one that can handle a 2" thick roll of magnetic tape is indeed a monster, but you have to have one. I've used tiny ones like the VCR tape variety for my 10" 1/4" reels and it works fine, but you need to move smoothly and take it away carefully to avoid a bump.

Degaussers are generally of two types. Those that use pulses and the most common ones which are continuous. The continuous duty ones can get hot pretty fast, so they will have a duty cycle. Very large commercial units avoid this by having fans built in.

For floppies, it is not nearly as important because they are digital and thus recorded to saturation. However, if there is an anomaly of any kind which is situated off track or a track is wide (360) and you put it in a narrow track (1.2) machine, the simplest way is to use the degausser. It is also so fast, simple, and effortless a way to guarantee results that any other method seems a waste of time.

I have little experience with them, but from all my reading, DAT tapes are difficult to erase. Again, being recorded to saturation, there is not a background problem. They're also dirt cheap, being under 20 bucks as opposed to over 200 for the 2" rolls. Many studios really liked them when they came out.

Degaussing in the digital realm is most often done for security reasons. Audio recording and floppy recycling, are really a special case. Yes, hard drives are also demagnetized. A quick Google will find you some commercial units for this.

Another common type of degausser, is the little hand held ones with the pointy ends for doing recording heads. Again, these are absolutely mandatory for audio work. In a commercial studio it's a daily morning routine. For home recording perhaps once a week or month. But you have to do it or you will soon loose high end.

Digital recording media such as we generally talk about here is really crude. Bang, the poles get hammered one way, and bang, they get hammered another way. Comparing digital to analogue magnetic media is like comparing a hammer and a camel hair brush.

I bought one of the older Radio Shack "bulk erasers" about two weeks ago. I call it my little "EMP" weapon.

The first time I used it I tried it on a 3.5" diskette. I got a little surprise when I got the diskette close to the bulk eraser - it jumped to make contact. Anything that buzzes in your hand is probably dangerous near electronics.

As MikeS pointed out, do not go near a hard drive with one of these. For pretty much anything newer than an ST225 it would be the end of the hard drive. Most IDE and newer hard drives have dedicated servo tracks or servo IDs embedded in the data and there is no low-level format that can bring those back.


Mike

True, it would likely wipe out any firmware on the chips or fry the little embedded microboard, I guess you could try taking it apart and just degauss the platters but still, a lot of work for something that's typically used for "sensitive" destruction of data. Classified data tends to go to the chipper.

Hi
It would surely do in any magnetic recording, such as a hard drive
but remember what I says. It would produce little voltage in firmware.
It takes many turns of even as strong field to create the voltage
needed to even turn on a diode.
Make a single loop of wire and put an AC meter leads to it.
With the coil about 6 inches away from the degausser, check the
voltage.
As I've said before, at least for floppies, recording is sensitive to
background fields that wouldn't seem to effect reading.
Placing color monitors on top of PC can cause write failures
on floppies. Spacing by as little as an additional 3 inches
can fix this.
Dwight

barythrin said:

True, it would likely wipe out any firmware on the chips or fry the little embedded microboard, I guess you could try taking it apart and just degauss the platters but still, a lot of work for something that's typically used for "sensitive" destruction of data. Classified data tends to go to the chipper.

Click to expand...

No, within reason a magnetic field such as a degausser creates is not going to affect the electronics (your "chips" or "microboards") at all, but there are patterns and data stored on the platters (especially on newer drives) that the drive needs in order to operate; they can not be (re)created outside of the factory so erasing them kills the drive.

To non-destructively erase data you normally just overwrite all tracks several times with meaningless patterns.

I finally obtained a Radio Shack style degausser, and it seems to work as intended on floppy disks. Some questions remain :

1. Degaussers do not seem to be able to "repair" floppy disks fully. I have a pair of HD 5.25" disks. One absolutely refused to read at all, the other could be read but all the data could not be copied from it (fortunately the data had been previously copied). After several seconds of degaussing, both disks completed a format, but both reported a substantial number of bad sectors, 50-110K. Are the disks truly damaged, or would more degaussing "fix" them?

2. Is there any harm in using a degausser on an ST-225 hard drive?

3. Will the metal shell of a modern hard drive prevent hard drive erasure if the degausser comes into contact with it?

I would guess the answers to these questions are as follows :

1. The disks are bad. Further degaussing may vary the number of bad sectors reported, but will not magically restore all of them to good sectors.

2. No, but you will need to low level format the drive afterward.

3. No, the relatively thin ferrous metal hard drive "case" will not shield the platters from the magnetic pulses.

Ole Juul said:

For floppies, it is not nearly as important because they are digital and thus recorded to saturation.

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I'd like clarification on this. The signals on floppies are encoded Frequency Modulation or Modified Frequency Modulation, so doesn't that mean that the base signal or carrier frequency is analog? The digital information is expressed by modulations to the carrier frequency, not by modulations to the amplitude of the signal. I'm sure the data encoding is more robust than analog audio tape, but the only form of saturation would be if the carrier frequency was being recorded at the maximum amplitude that the medium could absorb. That must be limited by the need to avoid printing through to the other side of the disk. Do I understand correctly?

Another common type of degausser, is the little hand held ones with the pointy ends for doing recording heads.

Click to expand...

Can those baby degaussers be used on floppy disks? I'm thinking of some kind of circular scrubbing action, like you might use polishing metal (not touching the surface, of course).

Rick

RickNel said:

I'd like clarification on this. The signals on floppies are encoded Frequency Modulation or Modified Frequency Modulation, so doesn't that mean that the base signal or carrier frequency is analog? The digital information is expressed by modulations to the carrier frequency, not by modulations to the amplitude of the signal. I'm sure the data encoding is more robust than analog audio tape, but the only form of saturation would be if the carrier frequency was being recorded at the maximum amplitude that the medium could absorb. That must be limited by the need to avoid printing through to the other side of the disk. Do I understand correctly?

Click to expand...

You likely know more about FM on floppies than I do. My point in differentiating between digital and analogue, is that with digital you are only concerned with ranges. With analogue such as audio, you cannot be out by even a microscopic amount or the whole thing is ruined. Any kink in the curve is audible, sometimes even as a click if it is over a short distance. With digital you ultimately only need to decode whether something is one side or the other of a range. No?

As for carrier frequency. In audio that is not recorded, but is just there to facilitate the process.

I've got to start being careful here, since I am not only rusty, but also liable to get out of my depth.

Can those baby degaussers be used on floppy disks? I'm thinking of some kind of circular scrubbing action, like you might use polishing metal (not touching the surface, of course).

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Absolutely not. They consist of a coil that is not more than 1.5" in diameter and 3" long. Out of the end of that comes a long probe. On the little Radio Shack ones the probe is about 2.5" and covered with plastic so as not to scratch anything. If you wiped a diskette with it, you would end up with a mess of degaussed stripes that were 1/8" wide. It is just not the right tool. The video tape ones which are still common, are exactly right. Larger equipment is only needed if you have to go through a roll of 2" tape.

Here is a picture of a roll of 2" tape, a cheap head demagnetiser, and a Realistic "magnetic bulk taper eraser".

I just got to thinking. (uh, oh) That what I should have said is that I don't think the encoding is relevant here. Whether it is frequency, time, amplitude, or any combination thereof, is not the issue. You ultimately only have to determine whether you are meeting one or the other of two conditions. That's even simpler than Morse, which as you know will survive a lot more noise than voice transmission. In fact, separating the information from the noise is the job at hand.

Dwight Elvey said:

Placing color monitors on top of PC can cause write failures
on floppies. Spacing by as little as an additional 3 inches
can fix this.

Click to expand...

To be fair, this applies only to some monitors and some PCs. The most recent example that comes to mind is the setup instructions for the IBM PCjr -- it warns not to put the color monitor on top of the system unit because it "interferes with the disk drive". The color monitor at the time the manual was being referenced was the IBM 5153, so that's why all the early PCjr advertising literature that showed a 5153 have it off to the side. The later PCjr-specific color monitor was designed to avoid that when placed directly on top of the case (I don't know how, but I suspect if I open one up I'll find a metal plate on the bottom).

I've definite seen floppies erased by setting them on top of an Amdek color monitor and then turning the monitor on. I don't know if it was the initial degaussing cycle of the monitor (most likely!) or the long rest time, but either way, after two hours, the disks had nothing on them.

All this talk about degaussing, I thought it would be worth mentioning a recent episode involving an MRI machine: MRIs use a ludicrously powerful magnet and it is warned that all metal objects and electronic devices be far removed from the scanning area before imaging begins. My wife is an MRI tech, and she told me recently of a patient who ignored cautionary advice and "smuggled" her iphone into the room in her pocket. iphones don't contain any ferrous metal so it didn't rip out of her pants and slam to the interior of the machine or anything, but a few seconds into the procedure the patient realized that a powerful magnet might not be the best thing for an electronic device so she stopped the scan... and found a completely bricked iphone.

Or so they thought. What actually happened was that phone going into the procedure had a full battery charge, and the MRI procedure managed to discharge the battery in less than a second. The phone was unresponsive plugging it into a USB cable + computer, but when plugged into a standalone charger cable, it started charging and was later fully operational, no data loss. The cable vs. standalone charger difference might be due to the USB cables providing 500 milliamps but wall plug chargers provide 1 amp, so maybe the additional amp was enough to "jumpstart" the charging process.

So, a 1.5 Tesla (about 45,000 times more powerful than the Earth's magnetic field) magnet can drain rechargeable batteries in a fraction of a second.

Trixter said:

the MRI procedure managed to discharge the battery in less than a second.

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How is that? Where did all the energy stored in the phone's battery go? (And that is a lot of energy).

Other than that I believe that iPhone does use some ferromagnetic materials: there are some transformers with ferrite cores, metal shielding, LCD frame, and even stainless steel screws will have considerable amount of iron in them. While it might not be enough to move the phone anywhere, when exposed to the changing magnetic field it heat up quite a bit. Not sure, perhaps it will even trigger some kind of thermal protection in the battery.

Magnetism:

Once upon a time, far, far away (Naval Station Kodiak, AK - 1961 or so) in the aircraft maintenance department's com/nav shop, a tech was making some adjustments on an airborne APS-20 search radar while it was on the test bench. Someone inadvertenly powered-up the system and when the maggy (magnetron) fired, a nearby phillips head screw driver was launched off the edge of the bench and impaled the tech's palm against the cavity. So, be careful with those magnetic fields (lol). I don't think your gold fillings or lower bridge are in much danger from a Radio Shack degausser, but . . .