jeffj@pedsga.UUCP (09/26/88)
I have a question worthy of the net's collective wisdom. My hearing extends into the high frequency end (>15kHz). I can hear several terminals and televisions 'squeal'. I understand that this is the flyback transformer at the scan frequency. Is there anything I can do to attentuate the squeal? How about a coating on the transformer? Inside the cabinet? I'm not interested in TEMPEST conformance, just reducing my headaches. Isn't there an OSHA limit for such stuff? Jeffrey Jonas allegra!io!mtune!petsd!pedsga!jeffj decvax!mcnc!rutgers!petsd!pedsga!jeffj
morganh@titus.gwd.tek.com (morganh) (09/28/88)
In article <716@pedsga.UUCP> jeffj@pedsga.UUCP writes: >I have a question worthy of the net's collective wisdom. >My hearing extends into the high frequency end (>15kHz). > >I can hear several terminals and televisions 'squeal'. >I understand that this is the flyback transformer at the scan frequency. > >Is there anything I can do to attentuate the squeal? >... :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) Have I got a solution for you! It includes (1) John Deere model MC Crawler Tractor sans muffler (the old two-cylinder "poppin johnny"), several older chainsaws in which the exhaust baffles have been eaten through, and .44 magum and .375 magnum handguns. Mix well with a lack of ear protection and sheer stupidity over a number of years. I am a glowing example of the efficacy of this treatment. I haven't been bothered by outside high frequency sounds in years. My ears begin rolling off at about 4500 Hz (of course the tinnitus keeps my desire for high frequency sound satisfied with CONTINOUS mixed squeals..) :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) Seriously, however, when I could hear such things (working on old TV sets), it was almost always connected to some sort of corona discharge around the flyback. You might check with a local supplier for what we used to call "Corona Dope" -- it used to solve the problem for me. To diagnose, try operating the monitor in a pitch black room with the back off. Morgan
jeffw@midas.TEK.COM (Jeff Winslow) (09/28/88)
In article <716@pedsga.UUCP> jeffj@pedsga.UUCP writes: >I can hear several terminals and televisions 'squeal'. >I understand that this is the flyback transformer at the scan frequency. True. Sometimes, however, you're hearing instability in the switching power supply often used in these units. This happens more often than you might think, even with supposedly "perfected" and "professional" designs. These noises are almost always pitched lower and are (to me) much more irritating that the scan frequency. >Is there anything I can do to attentuate the squeal? When my terminal squeals, I drop its back end on the desk from about 1/2" up. Most of the time it quits, so I suspect the transformer mounting is a bit, ah, flexible. Funny thing - I just tried it out and it caused the noise to *start*. I had to drop the front from about an inch up - twice - to get it to stop. Isn't this fascinating? :-) Jeff Winslow
jps@wucs1.wustl.edu (James Sterbenz) (09/29/88)
In article <716@pedsga.UUCP> jeffj@pedsga.UUCP writes: >I have a question worthy of the net's collective wisdom. >My hearing extends into the high frequency end (>15kHz). >I can hear several terminals and televisions 'squeal'. >I understand that this is the flyback transformer at the scan frequency. >Is there anything I can do to attentuate the squeal? >How about a coating on the transformer? Inside the cabinet? I've got the same problem, and with TV monitors, as well. Last time I tested, I could hear above 23KHz. While using one particular set of terminals I had to use ear plugs. If you have to resort to this, try using the little foam cylindrical ones. Thery're very comfortable. Now, I just use a portable CD, which seems to mask most of the noise (and monitors seem to be getting better, in general, and I suppose I'm starting to lose high frequency response with age). BTW, who ever thought that 22.04KHz frequency response was adequate for CD's? -- James Sterbenz Computer and Communications Research Center Washington University in St. Louis 314-726-4203 INTERNET: jps@wucs1.wustl.edu UUCP: wucs1!jps@uunet.uu.net
wolfgang@mgm.mit.edu (Wolfgang Rupprecht) (09/29/88)
In article <716@pedsga.UUCP> jeffj@pedsga.UUCP writes: >I can hear several terminals and televisions 'squeal'. I understand >that this is the flyback transformer at the scan frequency. Is there >anything I can do to attentuate the squeal? High frequencies are very easy to absorb. I have had lots of success in quieting flyback vibrations using GE's "RTV Silicon Rubber Adhesive Sealant". First unplug the power cord, and discharge the flyback's HV section and keep it shorted to frame ground for the duration of the hacking. Then disassemble the flyback mounting (and powdered iron core if possible). Pack RTV in every crack and mating surface you can find. Be generous here. Reassemble everything. Lastly remove the HV shorting strap, and plug back in. Be extremely careful when playing with the flyback. The HV section packs enough wallop to kill you, if improperly handled. -wolfgang --- Wolfgang Rupprecht ARPA: wolfgang@mgm.mit.edu (IP 18.82.0.114) TEL: (617) 267-4365 UUCP: mit-eddie!mgm.mit.edu!wolfgang
markz@ssc.UUCP (Mark Zenier) (10/01/88)
In article <716@pedsga.UUCP>, jeffj@pedsga.UUCP writes: > > I can hear several terminals and televisions 'squeal'. > I understand that this is the flyback transformer at the scan frequency. > > Is there anything I can do to attentuate the squeal? > How about a coating on the transformer? Inside the cabinet? Its usually the mounting hardware for the HV transformer. Try tightening the mounting hardware. Or rubber wedges around the transfomer coil. or just spreading a bunch of silicone caulk around the rectangular ferrite tranformer core. Mark Zenier uunet!pilchuck!ssc!markz "He did decide, though, that with more time and a great deal of mental effort, he could probably turn the activity into an acceptable perversion"-Mick Farren
sleat@ardent.UUCP (Michael Sleator) (10/06/88)
Several people have suggested mechanically damping the flyback transformer
to reduce the squeal. Good advice, I believe, but if it's an open frame
construction I'd caution you to be careful of the wires leading from the
windings to the terminals. They tend to be fragile. Also, don't
use just any old goop, because there are some fairly high voltages even
on the primary side.
I've run into one case where mechanical damping didn't help at all because
the sound was coming from elsewhere. It turned out that the retrace
capacitor was acting as a very effective transducer. The solution in this
case was to switch to a different style of capacitor. Both were epoxy-
dipped mylar types, but one must have been more loosely wound. This was
a manufacturing situation, and all of one vendor's caps seemed to exhibit
the same behavior, so we just switched vendors. (I think that the good
ones were Sprague "Orange Drops", but I don't remember for sure.)
Michael Sleator
Ardent Computer
...!{decwrl | hplabs | ubvax |uunet}!ardent!sleatrdi@cci632.UUCP (Rick Inzero) (10/11/88)
In article <716@pedsga.UUCP> jeffj@pedsga.UUCP writes: > >I can hear several terminals and televisions 'squeal'. > >Isn't there an OSHA limit for such stuff? My 1986 Buick Skylark has one of those digital electronic (blue fluorescent) dashboards, and it produces a whine that I can hear quite well. I can hear the whine even with the engine running and the radio on. I wish someboby would set a limit on this noise!! It's so loud (to me), that I suppose it would be near deafining to a child (with even better hearing than an adult). Anyway... For the first six months I owned the car the whine *REALLY* bothered me (my wife couldn't hear it); I even took it to the dealer (who thought I was imagining it), without success. Since the electronics are inaccessible in the dash, and I wasn't about to resell a brand new car, I finally learned to *IGNORE* it. The whine never bothers me any more, and I really don't perceive it unless I actually concentrate on hearing it. Maybe you can learn to "tune out" the squeal yourself as well... -- Rick Inzero rochester!cci632!rdi Computer Consoles Inc. (CCI) uunet!ccicpg!cci632!rdi Rochester, NY uunet!rlgvax!cci632!rdi
jlh@loral.UUCP (Physically Pffft) (10/13/88)
In article <19534@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes: =In article <716@pedsga.UUCP> jeffj@pedsga.UUCP writes: => =>I can hear several terminals and televisions 'squeal'. => =My 1986 Buick Skylark has one of those digital electronic (blue fluorescent) =dashboards, and it produces a whine that I can hear quite well. =For the first six months I owned the car the whine *REALLY* bothered me (my =wife couldn't hear it); I even took it to the dealer (who thought I was =imagining it), without success. =I finally learned to *IGNORE* it. Have you tried listening to heavy metal music at high volumes for long periods of time? Maybe even catch an Ozzy Osbourne or Queensrych concert? Worked for me, I haven't heard a high pitched squeal in years. Jim (ehh?, speak up) -- Jim Harkins Loral Instrumentation, San Diego {ucbvax, ittvax!dcdwest, akgua, decvax, ihnp4}!ucsd!sdcc6!loral!jlh