sorka@ucscb.UCSC.EDU (Alan Waterman) (01/02/90)
When I turn my TV off, areas around the center of the screen dance around brightly in multicolored flames. It is quite pretty but I can't seem to explain it. Unplugging the set has no effect. It still continues for about 10 minutes before dying out. Now this is an active flaming that changes shape and color quite rapidly. Note: this is not the effect you get when turning the set off in a dark room where you can see the whole screen] lit up faintly. The only thing that is possible is that the phosphorus is being bombarded by electrons, but how can this be if the power is turned off? Is the CRT drawing on capacitors or something? So what do people think?
sorka@ucscb.UCSC.EDU (Alan Waterman) (01/03/90)
How about getting a reply to this question. I'm very curious. Any theories?
random@cbnewse.ATT.COM (Random @ rebmA) (01/04/90)
From article <6834@lindy.Stanford.EDU>, by sorka@ucscb.UCSC.EDU (Alan Waterman): > > How about getting a reply to this question. I'm very curious. Any theories? I didn't see a question, but I'll comment on the subject line. My Scott brand monitor shows slowly fading splashes of color after power-down which I've just written off as the color guns still emitting after the set is switched to 'STANDBY'. Ive never unplugged the set at this point, but that may not have an influence, since there are still high capacitor potentials on the tube after power is removed. Random
myers@hpfcdj.HP.COM (Bob Myers) (01/04/90)
>When I turn my TV off, areas around the center of the screen dance around >brightly in multicolored flames. It is quite pretty but I can't seem to >explain it. Unplugging the set has no effect. It still continues for >about 10 minutes before dying out. Now this is an active flaming that >changes shape and color quite rapidly. Note: this is not the effect you get >when turning the set off in a dark room where you can see the whole screen] >lit up faintly. > >The only thing that is possible is that the phosphorus is being bombarded >by electrons, but how can this be if the power is turned off? Is the CRT >drawing on capacitors or something? First of all, it's "phosphor", not "phosphorus." Phosphorus is a rather nasty substance that doesn't have anything to do with the light-emitting chemicals used in CRT screens. CRT phosphors are for the most part (at least nowadays) various sulfide compounds. With that said, I can't come up with a good explantion for the phenomona you're describing, IF you really meant to say "10 minutes" rather than "10 seconds." I can certainly understand the tube still emitting considerable light for several seconds after the power is removed - esp. if the set is the "instant-on" variety, and leaves the power on the tube filament at all times. The "dancing colors" would be caused by "random" magnetic fields as various deflection and color correction circuits in the set shut down, or by external fields (if you've got the set next to something with a fair-sized motor, for example). However, I'm at a bit of a loss to explain how this would go on, in a normal, functional CRT, with any brightness at all for the period you describe. You sure no one in your house has tampered with the drinking water? :-) :-) :-) Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers%hpfcla@hplabs.hp.com | sentient life-form on this planet.
brad@optilink.UUCP (Brad Yearwood) (01/04/90)
In article <6805@lindy.Stanford.EDU>, sorka@ucscb.UCSC.EDU (Alan Waterman) writes: > > When I turn my TV off, areas around the center of the screen dance around > brightly in multicolored flames... > > The only thing that is possible is that the phosphorus is being bombarded > by electrons, but how can this be if the power is turned off? Is the CRT > drawing on capacitors or something? You have capacitance in the picture tube itself and in the high voltage system (diode/capacitor voltage multipliers are frequently used), so the screen of the tube may still be charged to a high potential even with all power turned off. This is why repair people (the surviving population thereof) remember to discharge the high voltage supply anode _and_ the picture tube anode connection before sticking their hands into a TV set or monitor. You have a cathode which, though no longer being actively heated, is still hot. It is reasonable to expect that the cathode will emit quite a few electrons, and that many of these will find their way to the positively charged phosphor screen, until the cathode cools or the charge dissipates (which process is of course helped along by these same electrons). Remember also that the cathode is working within an excellent vacuum, so it will cool only by radiation and by conduction through its connections and support structures. Brad Yearwood {pyramid, tekbspa, pixar}!optilink!brad
t33894v@kaira.hut.fi (Ari McPaananen) (01/04/90)
In article <12385@cbnewse.ATT.COM> random@cbnewse.ATT.COM (Random @ rebmA) writes: >My Scott brand monitor shows slowly fading splashes of color after >power-down which I've just written off as the color guns still emitting >after the set is switched to 'STANDBY'. Ive never unplugged the set You could also try this one: - Place TV to a dark room. Don't switch the set on. - Place an UV-lamp next to the screen. A 60W 'black-light' bulb will do too. - Illuminate the screen for a few seconds. Don't look at te light yourself. - Turn off the light and watch the screen glow. ############################################################################## # ygolonhceT fo ytisrevinU iknisleH, nenanaaP irA ! paananen@hupu.hut.fi # # ecneicS retupmoC fo .tped ! t33894v@kaira.hut.fi # # * DXers never die, they just fade out * ! paananen@otax.hut.fi #
sewilco@datapg.MN.ORG (Scot E Wilcoxon) (01/05/90)
In article <12385@cbnewse.ATT.COM> random@cbnewse.ATT.COM (Random @ rebmA) writes: >My Scott brand monitor shows slowly fading splashes of color after >power-down... My RCA TV set does the same thing if no image is being displayed when the power is turned off. If no signal is being given to the TV input, such as the cable converter box or a video game being turned off before the TV is turned off, several colored splotches appear. I've only waited a half hour for the splotches to fade before giving up and turning it off the way which works right. -- Scot E. Wilcoxon sewilco@DataPg.MN.ORG {amdahl|hpda}!bungia!datapg!sewilco Data Progress UNIX masts & rigging +1 612-825-2607 uunet!datapg!sewilco I'm just reversing entropy while waiting for the Big Crunch.
sorka@ucscb.UCSC.EDU (Alan Waterman) (01/05/90)
Actually, it is more like 15 minutes. No there is no motor of any kind near it and the screen stays BRIGHTLY lit even with the set unplugged.
rdi@cci632.UUCP (Rick Inzero) (01/06/90)
In article <6893@lindy.Stanford.EDU> sorka@ucscb.UCSC.EDU (Alan Waterman) writes: > >Actually, it is more like 15 minutes. No there is no motor of any kind >near it and the screen stays BRIGHTLY lit even with the set unplugged. ^^^^^^^^^^^^^^^^^^^^^^^^^^ See, that's what you get for renting that inexpensive apartment right under those high tension wires!! :-) :-) :-) --- Rick Inzero rochester!cci632!rdi Computer Consoles Inc. (CCI) uunet!ccicpg!cci632!rdi Rochester, NY uunet!rlgvax!cci632!rdi "Every time I hear that weasel tune, something pops inside of me, then everything goes black." - Curley Howard in "Punch Drunks", 1934
jones@hood (Clark Jones) (01/08/90)
In article <32965@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes: >In article <6893@lindy.Stanford.EDU> sorka@ucscb.UCSC.EDU (Alan Waterman) writes: >> >>Actually, it is more like 15 minutes. No there is no motor of any kind >>near it and the screen stays BRIGHTLY lit even with the set unplugged. > ^^^^^^^^^^^^^^^^^^^^^^^^^^ > >See, that's what you get for renting that inexpensive apartment right >under those high tension wires!! :-) :-) :-) Seriously, I'd be inclined to dig out the geiger counter and check for ionizing radiation in the area. I know of one rock hound whos 'counter went wild in his bedroom many years ago... turned out the Mexican tiles that formed the top of his nightstand were "hot"... also, I've heard many disturbing stories from archaeologists, who, in recent years, have been getting interested in chemical analysis of pot shards: Chaco Canyon in NM has supposedly produced some pottery so "hot" it can't be stored where people normally are (and Indians were at one time eating out of this stuff!) Anyway, ionizing radiation can make phosphors glow just as well as electron beams: the phospors are only interested in the right amount of energy, not in what provides it! Clark Disclaimer: The opinions expressed above are mine and not those of Schlumberger because they are NOT covered by the patent agreement!
sorka@ucscb.UCSC.EDU (Alan Waterman) (01/09/90)
But not in the same continual pattern. And besides, it does it from one house to the next when the tv is moved.
jones@hood (Clark Jones) (01/10/90)
In article <6967@lindy.Stanford.EDU> sorka@ucscb.UCSC.EDU (Alan Waterman) writes: > >But not in the same continual pattern. And besides, it does it from one house >to the next when the tv is moved. (I believe that this was in reply to my suggestion about radioactivity, so that is what I'm following up on...) Ionizing radiation would generally _NOT_ cause a "same continual pattern". It would vary significantly over time. Is anything besides the TV moved from house to house? The probablility of several houses having similarly "hot" rebar/bricks/whatever is fairly small, but if you are like me and have several other items that you like to take with you when you move, maybe one of them is "hot" :-) Actually, it could even be part of the TV itself that's "hot". Another, possibly somewhat more likely possibility is that the effect you are seeing is connected with the "degaussing" circuitry of the TV. Clark Disclaimer: The opinions expressed above are mine and not those of Schlumberger because they are NOT covered by the patent agreement!
wiz@xroads.UUCP (Mike Carter) (01/10/90)
In article <6805@lindy.Stanford.EDU> sorka@ucscb.UCSC.EDU (Alan Waterman) writes: > >brightly in multicolored flames. It is quite pretty but I can't seem to >explain it. Unplugging the set has no effect. It still continues for >about 10 minutes before dying out. Now this is an active flaming that >when turning the set off in a dark room where you can see the whole screen] >lit up faintly. > >The only thing that is possible is that the phosphorus is being bombarded >by electrons, but how can this be if the power is turned off? Is the CRT >drawing on capacitors or something? Someone once mentioned a similiar effect on a TV set quite a number of years ago . The explanation given was never proven, but it sounded feasable enough at the time. It was said that since all tubes store HV after the power is turned off, sometimes if a bleeder resistor is bad or if there is a nick or cut on any of the HV parts that discharging through ionization can cause electrons to spin off and bombard the screen....but in your case I'm stumped because this explanation would mean that the bombardment would have to be focused or there would have to be a scratched off area of the coating of the outside part of the tube. Well, since this is being written 200 messages down from the top of the heap, I'm sure someone else knows what it is. Sounds interesting tho. -Mike N7GYX G A R G O Y L E BBS (602)943-4523
torkil@psivax.UUCP (Torkil Hammer) (01/10/90)
Relax, folks. There is a natural explanation for funny afterimages on a TV screen. 1. Afterglow. You get afterglow from the "phosphor" (actually some less dangerous chemical) when it has been activated either by electrons making a TV picture, or by room lighting. Afterglow lasts for hours. Try covering half of the TV screen and expose it with a lamp, then turn off all room light and watch the show. 2. Electrostatic buildup. When the TV is on, electrons travel from the cathode to the phosphor, then have to find their way home, usually through some resistive carbon film. When the stream is cut off, the decay lasts for something like 3 seconds and forms a peculiar pattern on the screen.
sorka@ucscb.UCSC.EDU (Alan Waterman) (01/10/90)
Maybe I should have been even more specific. We moved just the TV and nothing else for the purpose of seeing if the TV still did it. It did and in the same pattern. It is not coming from ionizing radiation.
mahler@latcs1.oz.au (Daniel Mahler) (01/14/90)
In article <6805@lindy.Stanford.EDU> you write: > >When I turn my TV off, areas around the center of the screen dance around >brightly in multicolored flames. It is quite pretty but I can't seem to >explain it. Unplugging the set has no effect. It still continues for >about 10 minutes before dying out. Now this is an active flaming that >changes shape and color quite rapidly. Well, how about this: A static charge builds up on the front of the tube while the set is on. To prove this, just run your hand over the screen just after you've switched it off - you'll hear the crackling as it discharges to your hand (there's not enough there to hurt you - I have done this frequently before.) Once the set is switched off, the charge on the front of the tube leaks (through the screen front? This seems most likely to explain the phenomenon you describe) until it's discharged completely, and its energy is displayed to you in the form of a light show. Note that this doesn't depend on geographic location, the set being plugged in, radiation being nearby (which would provide a constant glow, not one that only lasts 10 minutes), or indeed anything other than that the set have been on recently. Incidently, running your hand over the screen is harmless because the charge you're conducting is only from a small part of the screen - the rest of the screen won't discharge because glass is such a good insulator (which incidentally is the reason the charge is held so well.) Don't (as I tried one day) cut a lump of foil, cover the screen, and discharge through that. (The things we do for knowledge...) This may not be the real cause of the phenomenon, but it's easily tested - just run your hand over the screen after you turn it off. If the effect goes away, this is the reason. ----------------------------------------------------------------------- ----------------No .sig, since I'm brain dead at present.-------------- -----------"What is the world to a man whose wife is a widow?"--------- -----------------------------------------------------------------------
michael@xanadu.com (Michael McClary) (02/02/90)
In article <6967@lindy.Stanford.EDU> sorka@ucscb.UCSC.EDU (Alan Waterman) writes: > >But not in the same continual pattern. And besides, it does it from one house >to the next when the tv is moved. Picture tube illumination after powerdown is a standard phenomenon. There is a lot of energy stored in the charge on the second anode, and the cathode(s) stay hot enough to emit for quite a while. Once the power and sweep stop, and the voltage on the control grid and focus anode go out of spec, a spot will appear (slowly moving and changing shape as the fields continue to change) and stay visible until the cathodes finally cool or the second anode is sufficiently discharged. 15 minutes is not unreasonable. (On color displays you get three separate spots, because the beam convergence fields have also gone goofy.) If you've let the set stabilize before you shut it down, the spot(s) will always follow the same track. With the sweep off, the beam current can be enough to burn the phosphor after many shutdowns. Because of this, most TV and monitor designs either don't let the control-grid(s) go to turn-on bias after shutdown or are arranged to turn the beam(s) full-on as the power fails, to discharge the second anode in a single shutdown flash while the sweep decays. Obviously, your monitor either lacks discharge-flash circuitry or has a defect. Note that, even if a monitor DOES do a discharge-flash, the second anode can still have enough charge to throw you across the room after the flash is done.