CurtPalme.com Home Theater Forum

deronmoped · Joined: 03 Nov 2006 Posts: 1154 Location: San Diego

Anyone have any experience with degaussing? I keep coming back to thinking about degaussing my 10PG just to see if there can be a improvement had. Now some of the PG's have a degaussing circuit in it and they say in the manual it must be done just after installing the PJ, I guess at some point the engineers convinced the sales department a degaussing circuit was necessary. Now the only problems I can see with having a magnetic field near the CRT's is, it would increase the spot size of the beam and throw off the convergence. I'm guessing that the steel in the chassis is the only thing that would have to be demagnetized. I could do a quick test to see if there was a problem with magnetized steel, just get a big chunk of steel and bring it near the CRT's with a spot pattern up and see what it does.

Deron.

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

Curt is The Expert, but that's never stopped me from opening my trap... Smile

Degaussing is something you do to direct-view TVs. The shadow mask can get magnetized and that throws off the electron beam, resulting in the beam hitting the wrong color phosphors and doing Bad Things to your picture. PJs don't have shadow masks so you don't have to worry about degaussing them -- at least not the tubes themselves.

Could some other part of the PJ get magnetized? I suppose, if it's ferrous. Unistrut can very possibly get magnetized. But I don't think it's going to mess with your spot size. All it would do is bend the electron beam a bit, and your convergence/etc would just correct for it, just like it corrects for the localized geomagnetic field. As long as the magnetic field isn't extremely strong, and doesn't move, I really doubt it would hurt anything.

Fujifrontier · Joined: 20 Oct 2007 Posts: 354 Location: San Antonio, Texas

Thank you for asking this question; it's something I've wanted to know for awhile too.

**AnalogRocks** · Posted: Thu Nov 15, 2007 1:59 am Post subject:

If you do try degausing remember to put your bank cards and credit cards away from where you are working. Don't ask me how I know that LOL.

**Curt Palme** · Posted: Thu Nov 15, 2007 2:13 am Post subject:

Umm, I want to know too.. Wink

The + and the Xtras have the degaussing circuits in them, and I've activated them post quickie setup at the shop, and have never seen any difference.

Someone like John Gannon or Ken Whitcomb really need to answer this as to why the circuits are in there. Doug? Mike?

tse · Joined: 03 May 2006 Posts: 1014 Location: Sweatbucket, Fl.

Do not the NEC projectors with the degaussing coils have steel chassis parts? That stuff could maybe become magnetised. Most projectors are made with aluminum and other non-magnetic parts.

Scott

deronmoped · Joined: 03 Nov 2006 Posts: 1154 Location: San Diego

Yeah, you have a steel chassis surrounding the tubes, if that chassis has any magnetism to it, the beam could be pulled in all directions at once. If that happened I think it could mess with the spot size. The Earth has it's magnetic field and it is recommended that we correct for that.

I'm gong to get a degaussing coil and experiment around with it to see what it does. Right now at 960P the green is the sharpest, you can see the dashes the focus letters are made up of, there is a scattering of light around the letters though, kinda like a halo. The blue I'm really do not spend that much time on as you defocus it anyways, it's about as sharp as the green. The red is just starting to show the dashes, there is something wrong there, not sure what, it should be as sharp as the green. I'm hoping with the degaussing coil I can correct that halo that shows up around the letters.

Deron.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

I would be very careful with that degaussing coil and especially would not use it near the neck of the tube. It can damage the parts in the neck. The coils that are built in, such as those in the NEC's are very low current just like those in all direct view tv's. The reason for external degaussing coils is sometimes the internal ones cannot remove the magnetizum because of lack of enough current so you must use the more powerful external ones.

deronmoped · Joined: 03 Nov 2006 Posts: 1154 Location: San Diego

So I did it. I tried out a quick degaussing of my 10PG last night. About the only thing I noticed is, I had to set the tilt and skew to zero on the red tube and turn the yoke to line up the pattern. I'm almost using no tilt and skew on the red now, it's like two clicks on each. Not sure what the degaussing changed, but it was for the better. I was hoping it would fix my linearity and improve the focus, did not see any change there. The chassis is still magnetized, it's swings a compass when I bring that close to it, I may try it again.

Deron.

David_Web · Joined: 02 May 2007 Posts: 418 Location: Sweden

A compass is a magnet. So if the chassis is ferrous it will affect the compass regardless if it's magnetized or not.

deronmoped · Joined: 03 Nov 2006 Posts: 1154 Location: San Diego

David

Dam, your right, now how do I tell if something needs demagnetizing?

Deron.

David_Web · Joined: 02 May 2007 Posts: 418 Location: Sweden

You could hold something ferrous but not magnetized in a rope near it. If it gets attracted to the chassis you will know the chassis acts as a magnet.
You will have to make sure the object is light and not magnetized nor charged.
Might not be sensitive enough thought.

Hall sensor might also work.

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

Hmmm, could hook up a coil of wire (lots of windings preferably) to a millivolt-scale DVM and wave the coil next to all the parts of the PJ. Any magnetic fields should generate a current in the coil. Not sure how sensitive this would be, so it might show a signal for very low levels of magnetism that are too low to worry about.