tom@syssoft.com (Rodentia) (06/13/91)
All of this talk of squealing TV's reminds me that I have a stereo speaker too
close to my TV. When the green intensity of the displayed picture is low, I
get a green blob in the lower right (closest to speaker) corner. Moving the
speaker when the TV is already on doesn't help much, but moving it when the
TV is off and then turning it on solves the problem. I assume this indicates
that the TV degausses the tube whenever turned on.
So, am I damaging my TV by operating it in this fashion? What about the
speakers? For reference, it's a 27" Sylvania (about 3 years old).
Also, is there a practical magnetic shielding, or would I need some
yttrium-copper-oxide and a mess of liquid nitrogen ;-{) ? Thanks.
--
Thomas Roden | tom@syssoft.com
Systems and Software, Inc. | Voice: (714) 833-1700 x454
"If the Beagle had sailed here, Darwin would have | FAX: (714) 833-1900
come up with a different theory altogether." - me |mcovingt@athena.cs.uga.edu (Michael A. Covington) (06/17/91)
The usual magnetic shielding material is mu-metal. The cheapest way to get some is to go to a hamfest (flea market) and buy a couple of dead oscilloscopes that have mu-metal shields around their CRTs. But I'm told that mu-metal is brittle and you can't just unbend it. -- ------------------------------------------------------- Michael A. Covington | Artificial Intelligence Programs The University of Georgia | Athens, GA 30602 U.S.A. -------------------------------------------------------
frankb@hpsad.HP.COM (Frank Ball) (06/19/91)
/ mcovingt@athena.cs.uga.edu (Michael A. Covington) / 10:20 am Jun 16, 1991 / *The usual magnetic shielding material is mu-metal. The cheapest way to *get some is to go to a hamfest (flea market) and buy a couple of dead *oscilloscopes that have mu-metal shields around their CRTs. But I'm told *that mu-metal is brittle and you can't just unbend it. You can unbend it, but its magnetic properties deteriorate significantly. There is an annealling process to restore it, but its not something you can do at home. Try using ordinary sheet steel. Frank Ball frankb@hpsad.HP.COM pyramid!hplabs!hpsad!frankb
brian@ucsd.Edu (Brian Kantor) (06/20/91)
You can get "tin plate" at large sheet metal stores. It's thin sheet steel with a tin plating on it, and is easily cut and bent with hand tools. You can make boxes out of it by soldering edges together with an ordinary soldering iron, and a simple coat of spray lacquer will keep it bright and shiny for years. If you don't need the ultimate in shielding, it will do well and is quite cheap. Just watch your fingers on the sharp edges. - Brian
clemon@lemsys.UUCP (Craig Lemon) (06/24/91)
In article <35995@ucsd.Edu> brian@ucsd.Edu (Brian Kantor) writes: >You can get "tin plate" at large sheet metal stores. It's thin sheet > - Brian >[...] I think we got away from the point for a second or two here. The answer I was waiting for was to the question "Does this operating environment damage the CRT?". Sometime I'm inclined to set a muffin fan (why do they call them "muffin" fans ? :-) on top of my montior (NEC Multisync IIA) as it gets quite warm after a while and cool is always better (usually :). When I do this I can notice a slight (_slight_) rippling effect in the picture if I look hard. I want to be sure that prolonged exposure to a magnetic field will not mess up my convergence or anything like that. I'm not sure whether the IIA degausses on power-up. Does anyone else know? -- Craig Lemon - Kitchener, Ontario. Amiga B2000 UUCPv1.13D. clemon@lemsys.UUCP lemsys!clemon@xenitec.on.ca | Please Mail any binaries xenitec!lemsys!clemon@watmath.waterloo.edu | to 'files' at this site ..!uunet!watmath!xenitec!lemsys!clemon | instead of 'clemon'
frankb@hpsad.HP.COM (Frank Ball) (06/25/91)
/ clemon@lemsys.UUCP (Craig Lemon) / 6:51 am Jun 24, 1991 /
*I think we got away from the point for a second or two here. The
*answer I was waiting for was to the question "Does this operating
*environment damage the CRT?". Sometime I'm inclined to set a muffin fan
*(why do they call them "muffin" fans ? :-) on top of my montior (NEC
*Multisync IIA) as it gets quite warm after a while and cool is always better
*(usually :). When I do this I can notice a slight (_slight_) rippling
*effect in the picture if I look hard. I want to be sure that prolonged
*exposure to a magnetic field will not mess up my convergence or anything
*like that. I'm not sure whether the IIA degausses on power-up. Does
*anyone else know?
Color TVs do degausse the tube on power-up, but they will only degausse
a mild magnetization on the grid (I think its called a grid, its a metal
plate full of little holes just behind the glass faceplate of the CRT).
When this plate gets magetized it bends the paths of the electrons and
distorts the picture, the colors get really strange. If you get a strong
enough magetization on the grid the degausse coil built into the set will
not do the job. It is possible to do it with a handheld AC electromagnet,
but it is very difficult to do a good job. I would avoid anything that
causes visible distortion on the screen, it is asking for trouble.
Frank Ball frankb@hpsad.HP.COM pyramid!hplabs!hpsad!frankbluns@spocom.guild.org (Luns Tee) (06/26/91)
frankb@hpsad.HP.COM (Frank Ball) writes: > a mild magnetization on the grid (I think its called a grid, its a metal > plate full of little holes just behind the glass faceplate of the CRT). It's called a Shadow Mask.
myers@hpfcrlm.HP.COM (Bob Myers) (06/27/91)
>(usually :). When I do this I can notice a slight (_slight_) rippling >effect in the picture if I look hard. I want to be sure that prolonged >exposure to a magnetic field will not mess up my convergence or anything >like that. I'm not sure whether the IIA degausses on power-up. Does >anyone else know? I don't know for sure whether the IIA degausses on power-up or not (you could tell by listening for an "AC power"-sort of hum for a few seconds when the monitor is powered up, after having been off for a minute or so). In any event, you're not likely to have convergence problems as the result of putting an *AC* fan on top of the display; the rippling you're seeing is just the AC field from the fan mucking around and beating with the deflection (the vertical deflection of the display is NOT locked to the line), and, since it's an AC field, it will not wind up magnetizing the tube structures (such as the shadow mask) and thereby cause purity and convergence problems. Even if it DID, degaussing the monitor is no big deal. You SHOULD always look for a monitor with built-in degaussing (auto or manual), but even those are likely to eventually need a pass with an external degaussing coil to keep things OK. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers@fc.hp.com | sentient life-form on this planet.
mzenier@polari.UUCP (Mark Zenier) (06/27/91)
In article <1840052@hpsad.HP.COM> frankb@hpsad.HP.COM (Frank Ball) writes: >Color TVs do degausse the tube on power-up, but they will only degausse >a mild magnetization on the grid (I think its called a grid, its a metal >plate full of little holes just behind the glass faceplate of the CRT). Mask or Shadowmask. The grids are back in the CRT gun assembly, and are usually dinnerplate or cylinder shaped, with a little hole in the center. Mark Zenier markz@ssc.uucp mzenier@polari.uucp