wtm@neoucom.UUCP (Bill Mayhew) (10/23/86)
Hi, After seeing the pletohora of articles about leaving one's computer turned on, I'm finally goaded to put in my two cents' worth. I agree that leaving the HDU powered up for long stretches of time is probably a good idea. In honesty, probably turning the computer off over night while one is away from the office is probably not going to be too much for the system and HDU to bear. The designers are indeed aware that this is normal behavior. Turning the computer off every time one gets up from the desk for a cup of coffee is probably a bad idea. Anyway, an IBM pc with 640K of memory takes an excruciatingly long time to power up, never mind the wear and tear!! Running "shipdisk" or whatever the HDU head parking program on your version of MS/PC DOS is called just before turning the power off is a good idea. My dad has a PC on a floor stand where he works. He lost the HDU when the cleaning crew slammed into the PC with a vacuum cleaner (with the system off). With the power on, ironically, the system probably would have survived the impact, due to the air cushion between the head and platter. The newer 3.5 inch based hardcards have a head unloading spring that automatically pulls the heads up when the power is off. They'll survive all but the most violent impact. Now for the real meat of this letter. Its a darn good idea to turn the monitor off (ie. no 110v going in, not just the intensity down) while everyone is out of the office. We have 50 or 60 terminals and monitors of various types around here, and have had several spontaneously catch fire in the CRT assembly. Fortunately, somebody has always been around to do something to put out the smoldering monitors. If it happened at 2:00 AM, we might have had a real mess. The problem is usually related to the high-voltage power supplies in the monitors. I've seen two failure modes. First, a lot of dust is attracted to the high voltage anode lead of the CRT due to the intense field. Inevitably, the dust causes leakage currents which then cause the flyback drive to incease and cause overheating in the horizontal drive transistor and associated circuitry. Method two failure relates to Televideo terminals. The horizontal output transistor is AC coupled to the flyback transformer by a nonpolarized capacitor which is under-rated. About 1 amp of current flows in the cap. which causes it to get very hot, even in normal operation. Eventally the cap shorts when the electrolyte dries out. Poof. I've replaced the HV power board in several televideos; now they're using a bigger cap, but the new caps still go bad after a while. Bill Bill Mayhew Division of Basic Medical Sciences Northeastern Ohio Universities' College of Medicine Rootstown, OH 44272 USA phone: 216-325-2511 (wtm@neucom.UUCP or ...!cbatt!neoucom!wtm , etc.)
gt6294b@gitpyr.gatech.EDU (SCHEUTZOW,MICHAEL J) (10/24/86)
> >Its a darn good idea to turn the monitor off ... >while everyone is out of the office. We have 50 or >60 terminals and monitors of various types around here, and have >had several spontaneously catch fire in the CRT assembly. > > [...elaborate technical reasons for terminals to set themselves > on fire...] > I find it difficult to believe that that many terminals or computers are on the verge of self-incineration, as implied by this posting. Now that the VDT-radiation scare has subsided, maybe it's time for a new crisis. Anyone else care to offer a humble opinion? Mike Scheutzow UUCP: gt6294b@gitpyr.uucp Georgia Tech ARPA: gt6294b@pyr.ocs.gatech.edu "We believe our computer system is better than many others, but we would be alarmed if it appreared to work perfectly. Fortunately, there seems to be no cause for alarm." (smoke detectors have been installed :-)
larry@kitty.UUCP (Larry Lippman) (10/25/86)
In article <2475@gitpyr.gatech.EDU>, gt6294b@gitpyr.gatech.EDU (SCHEUTZOW,MICHAEL J) writes: > >Its a darn good idea to turn the monitor off ... > >while everyone is out of the office. We have 50 or > >60 terminals and monitors of various types around here, and have > >had several spontaneously catch fire in the CRT assembly. > ... > I find it difficult to believe that that many terminals or computers > are on the verge of self-incineration, as implied by this posting. > > Now that the VDT-radiation scare has subsided, maybe it's time for a > new crisis. Anyone else care to offer a humble opinion? There is nothing in a CRT monitor which is any more prone to catch fire than in a computer itself. CRT monitors have no more than 24 volts DC present in any circuit element, with the exception of the high voltage accelerating potential circuit. Now, THAT circuit may well have 12 to 25 kilovolts of DC, but will be so current-limited (a few microamperes), that one would be hard-pressed to start a fire by intentionally removing the anode wire and arcing it between ground and a piece of paper! What else is there _different_ in a CRT that will burn? The deflection yoke? No way! Now, let's talk about a REAL VDT problem: I hear that VDT's cause an unhealthy buildup of negative phlogiston in the atmosphere... :-) ==> Larry Lippman @ Recognition Research Corp., Clarence, New York ==> UUCP: {allegra|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry ==> VOICE: 716/688-1231 {hplabs|ihnp4|seismo|utzoo}!/ ==> FAX: 716/741-9635 {G1,G2,G3} "Have you hugged your cat today?"
forbus@uiucdcsp.cs.uiuc.edu (10/26/86)
I have seen CRTs catch fire more than once. I have never seen CPUs or other peripherals catch fire. The earlier poster's arguments about voltages may sound appealing a priori, but does not jibe with experience. Shorts in HV systems, even though the current is low, can indeed lead to fires. Unless the machine involved has a serious disk or likes to live in a machine room, I turn the power off when I'm through with it for the day.
berger@clio.Uiuc.ARPA (10/26/86)
That's a relief. Now explain it to my monitor, which caught fire a few months ago.
skip@ubvax.UUCP (Stayton D Addison Jr) (10/27/86)
In article <302@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes: > ... > Now for the real meat of this letter. Its a darn good idea >to turn the monitor off (ie. no 110v going in, not just the >intensity down) while everyone is out of the office. We have 50 or > ... [stuff related to why one should turn off the monitor] Even with the power switch turned off, several monitors still drain a few milliamps. (Maybe for a cathode heater?) It would seem wise to turn off the power switch, but not the source of 110V power. An example is the IBM Color/Graphics Display. -- Skip Addison {lll-crg, decwrl, ihnp4}!amdcad!cae780!ubvax!skip or sun!amd!ubvax!skip
bill@hp-pcd.UUCP (bill) (10/27/86)
I seem to remember a few years ago we had an HP-87 prototype (personal desktop computer) catch fire. Problem was traced to a small bypass capacitor on a 6V supply; its dielectric material for some reason broke down and ignited. Further investigation showed that particular type of capacitor to be fairly prone to such failure. I don't remember whether we changed the type of capacitor, or switched to a different manufacturer, but using a different part did cure the problem. Don't overlook seemingly innocent components as potential problem spots. EVERYONE uses things like bypass capacitors just about EVERYWHERE (ever wonder what that little capacitor next to each chip in a RAM array was for?). The voltage doesn't really matter; as long as there's enough current to heat up anything that's shorted out, and the power supply doesn't see the problem and limit the current or shut itself down ... bill frolik hp-pcd!bill Hewlett-Packard Portable Computer Division Corvallis, Oregon
npollack@polyslo.UUCP (Neal Pollack) (10/28/86)
In article <1379@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: > > There is nothing in a CRT monitor which is any more prone to catch >fire than in a computer itself. > CRT monitors have no more than 24 volts DC present in any circuit >element, with the exception of the high voltage accelerating potential >circuit. Now, THAT circuit may well have 12 to 25 kilovolts of DC, but will >be so current-limited (a few microamperes), that one would be hard-pressed >to start a fire by intentionally removing the anode wire and arcing it between >ground and a piece of paper! > What else is there _different_ in a CRT that will burn? The >deflection yoke? No way! > >==> Larry Lippman @ Recognition Research Corp., Clarence, New York >==> UUCP: {allegra|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry >==> VOICE: 716/688-1231 {hplabs|ihnp4|seismo|utzoo}!/ No offense Mr. Larry Lippman, but you are giving users dangerous advice indicating that it is not realistic for a monitor to cause a fire. I have been a technician for 12 years, and an Engineer for the last 7. I have seen numerous fires started by both 5 volt logic, and high voltage in monitors. Netland people, do not fear your low voltage logic, it is rare to start a fire with the 5 volt levels. However, when it comes to the monitors, maybe Mr. Lippman can explain to our Fire Department why he thinks they can not burn. We have seen several monitor fires here over the last few years. They have ranged across many brands. In most cases, the high voltage section (10 -25 Kvolts) has started a fire by either arcing or internals shorts in the transformers. In one case, a power resistor in the power supply of a Tek Graphics terminal flamed out and set the board on fire overnight. In all cases, our smoke detectors alerted the fire crews before serious damage to the laboratory complex. Larry states, "you may be hard-pressed to ignite a piece of paper...". I say, and have seen, that you can easily destroy the entire terminal and maybe the building which houses it. The problem usually starts with a build-up of combustible dust, attracted by electro-static charge. The dust may absord moisture, which can then result in arcing. The arcing WILL cause the dust to burn, and hence the transformer and insulation will follow. Also, beware of people at your site that toss print-outs on top of a monitor (right over the cooling vents). Very expensive mistake if you don't like modern char-black wall-paper. Moral: Leave logic and hard-disk on. Turn monitors OFF !! This is the policy in our lab units. (P.S. Larry, I do not hate you, I just happen to be a safety type.) Neal Pollack Chief Engineer California Polytecnic State University Computer Science Department San Luis Obispo, CA 93407
corwin@cdp.UUCP (10/29/86)
Who is building all of these funky monitors which are catching fire?? This must be a recent phenomenon, perhaps cost cutting measures due to the "clone wars". In my 15 years' experience with computers, I've never seen a monitor flame on (other than reading these messages :-).
wtm@neoucom.UUCP (Bill Mayhew) (10/29/86)
Color monitors often draw a little bit of current when the front panel power switch is off. This is due to the fact that a de-gaussing coil is wrapped around the front edge of the CRT and supplied with a few mA of 60Hz current to prevent a static magnetic field from forming on the shadow mask and causing color blotches. The AC switch is often rigged to send a larger current for a few seconds right when the monitor is switched on to clean up any residual field. For these monitors, I'd leave them plugged in, but not turned on overnight (unless somebody is around, of course!). -------------original citation follows:-------------- In article <572@ubvax.UUCP>, skip@ubvax.UUCP (Stayton D Addison Jr) writes: > In article <302@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes: > > ... > > Now for the real meat of this letter. Its a darn good idea > >to turn the monitor off (ie. no 110v going in, not just the > >intensity down) while everyone is out of the office. We have 50 or > > ... [stuff related to why one should turn off the monitor] > > Even with the power switch turned off, several monitors still drain a few > milliamps. (Maybe for a cathode heater?) It would seem wise to turn off > the power switch, but not the source of 110V power. An example is the IBM > Color/Graphics Display. > > -- Skip Addison
spf@bonnie.ATT.COM (10/30/86)
I had a memory board in an image processor catch fire once when a capacitor popped. The cooling fans spread the heat across the board and scorched the plastic-or-whatever, resulting in vile smoke and (at least the evidence of) flames.
larry@kitty.UUCP (Larry Lippman) (10/31/86)
In article <220@polyslo.UUCP>, npollack@polyslo.UUCP (Neal Pollack) writes: > In article <1379@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: > > There is nothing in a CRT monitor which is any more prone to catch > >fire than in a computer itself. > > CRT monitors have no more than 24 volts DC present in any circuit > >element, with the exception of the high voltage accelerating potential > >circuit. Now, THAT circuit may well have 12 to 25 kilovolts of DC, but will > >be so current-limited (a few microamperes), that one would be hard-pressed > >to start a fire by intentionally removing the anode wire and arcing between > >ground and a piece of paper! > > What else is there _different_ in a CRT that will burn? The > >deflection yoke? No way! > > No offense Mr. Larry Lippman, but you are giving users dangerous > advice indicating that it is not realistic for a monitor to cause > a fire. I have been a technician for 12 years, and an Engineer > for the last 7. I have seen numerous fires started by both 5 volt > logic, and high voltage in monitors. Netland people, do not fear > your low voltage logic, it is rare to start a fire with the 5 volt > levels. However, when it comes to the monitors, maybe Mr. Lippman > can explain to our Fire Department why he thinks they can not burn. First of all, I am referring to CRT monitors which are mass-produced and therefore _should_ be UL approved. Like something made by NEC, Amdek, Ball, Conrac, RCA, etc. If you are using a monitor which is homebuilt, surplus, or otherwise NOT UL-aprroved, then ANYTHING is possible! Second, I am referring to monitors which are PROPERLY MAINTAINED. It should be obvious to anyone using a monitor for any period of time that the electrostatic charge results in dust buildup, especially on the CRT surface. Dust, of course, also builds up INSIDE the monitor - which is why all monitors should be opened at least once per year and vacuumed. Such cleaning is part of what I consider to be "proper maintenance". There is no question that a monitor with huge dust balls inside is a potential fire hazard (which is no different than carelessly storing oily rags...). As long as we are talking about UL-approved monitors that are reasonably dust free (which SHOULD be the case for everyone!), I stand by my original posting - a monitor should be no more prone to catch fire than any other computer circuitry. Notice that I said "more prone", and NOT "never". In a UL-approved monitor, you will find virtually no component - including the case - that is not a self-extinguishing plastic. This means that printed circuit boards are NOT phenolic, but are something like a FR-4 fiberglass-epoxy construction. Some catastrophic fault may result in SMOKE until power is removed through operation of either internal or external overcurrent devices, but it is highly unlikely that FIRE will result. Why? Because in order for a self-extinguishing plastic to burn - like FR-4 - it is necessary that external energy be applied. With the operation of an overcurrent device, this external source is removed. Sure, I've seen charred FR-4 - especially on boards where a fault occured that resulted in a wire-wound resistor getting red-hot. But once the resistor opened under overload, or the power was cut, say by a blown fuse, any FR-4 burning abruptly stopped. > We have seen several monitor fires here over the last few years. They > have ranged across many brands. In most cases, the high voltage > section (10 -25 Kvolts) has started a fire by either arcing or > internals shorts in the transformers. In the case of arcing, arcing against _what_? Most monitors use a horizontal output transformer with the high voltage lead running to an inline silicon rectifier array, and thence to the CRT anode. These silicon rectifier arrays will open rather quickly under the overcurrent conditions associated with arcing - thereby removing the source of the arcing energy. Should the horizontal output transformer develop a significant internal short, then invariably either the horizontal output transistor will fail due to overload, or the power supply overcurrent device will actuate. What is going to burn? Is this any DIFFERENT than the power supply transformer in a computer developing an internal short? > In one case, a power resistor > in the power supply of a Tek Graphics terminal flamed out and set > the board on fire overnight. This is a POWER SUPPLY PROBLEM. Is this any different than the computer itself? > In all cases, our smoke > detectors alerted the fire crews before serious damage to the > laboratory complex. Did the fire burn through the terminal housing? If not, was the terminal housing hot enough to blister paint and ignite say, paper left in contact with the terminal. Look, I'm not saying that monitors won't catch fire, and I'm not denying that monitors haven't caught fire in the past. There is a possibility of fire ANY time line-operated electronic equipment is involved. All I am saying is that for what should be a NORMAL situation (i.e., a properly maintained, UL-approved monitor), there is no greater probability of it catching fire than in say, the computer itself. ==> Larry Lippman @ Recognition Research Corp., Clarence, New York ==> UUCP: {allegra|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry ==> VOICE: 716/688-1231 {hplabs|ihnp4|seismo|utzoo}!/ ==> FAX: 716/741-9635 {G1,G2,G3} "Have you hugged your cat today?"
dmt@mtunb.UUCP (Dave Tutelman) (11/09/86)
In article <2475@gitpyr.gatech.EDU> gt6294b@gitpyr.UUCP (SCHEUTZOW,MICHAEL J) writes: >> >>Its a darn good idea to turn the monitor off ... >>while everyone is out of the office. We have 50 or >>60 terminals and monitors of various types around here, and have >>had several spontaneously catch fire in the CRT assembly. > >I find it difficult to believe that that many terminals or computers >are on the verge of self-incineration, as implied by this posting. > >Now that the VDT-radiation scare has subsided, maybe it's time for a >new crisis. Anyone else care to offer a humble opinion? > Where I work, there are LOTS of PCs and terminals, many of which get left on for long periods of time. I remember exactly ONE catching fire. It was a Concept [108?] terminal. A large lab FULL of computers and terminals started to smell, and we walked around sniffing till we found the offending equipment. To give you some idea of the probability: This is one of four similarly equipped labs. It has four minicomputers, four PCs and about two dozen terminals, most of which run continuously. This is the only such incident I can remember over the course of about three years. Assuming [contrary to fact] that this shred of data is statistically representative, the MTBF (Mean Time Between Fires) of this sort of equipment is about 3,000,000 hours, or about 300 years. By the way, some minicomputers ARE a fire hazard. In particular, if the machine will run hot enough to catch fire with [n-m] cooling fans SEIZED off (not just unpowered) and the other [m > 0] fans funning, you could get a REALLY nasty one. About a dozen years ago, DEC sent out a mod kit for PDP 9s and 15s, after a couple of really impressive fires. (I don't know if anybody still makes computers that indulge in self-immolation.) --------------------------------------------------------------- ---=== Dave Tutelman -------===== Physical - AT&T Information Systems ----------====== Room 1K218 ==--------======== 307 Middletown-Lincroft Rd. ====---========= Lincroft, NJ 07738 ============ Logical - ...ihnp4!mtuxo!mtunb!dmt ====== Audible - (201)-576-2442 ---------------------------------------------------------------