paluzzi@oddjob.UUCP (Greg Hajek) (01/15/86)
(To net.micro.mac readers: this has been an ongoing discussion in net.audio, but as this posting is a bit of a digression from audio talk, I have directed followups to n.s.m.) In article <251@birtch.UUCP> oleg@birtch.UUCP (Oleg Kiselev) writes: >> I've never encountered a TV receiver or monitor that >>didn't emit an annoying high pitched squeal at at least a >>low audible level. > >I have heard it is usually the vibration of transformers and/or capacitors >(fly-back transformer?????). THe worst offenders I have heard were >tvi925 . Sometimes a sharp rasp on the side of the terminal would silence >it for an hour or so ( and many people got so irritated by the squeal they >did it routinely). I have had the same problem with my Mac, and also found that the "sharp rasp" (read: "swift kick") solution is usually effective. Why is this? I never had the problem before I blew my power supply, and had to replace the analog board. Can anybody suggest a possible solution (or a reason why this problem would suddenly crop up, for that matter)? -- "God lives in Eternity...He doesn't have to listen to Two-for-Tuesdays." Greg Hajek U. of Chicago ...ihnp4!gargoyle!oddjob!paluzzi Laboratory for Astrophysics and Space Research
briand@tekig4.UUCP (Brian Diehm) (01/16/86)
>I have had the same problem with my Mac, and also found that the "sharp rasp" >(read: "swift kick") solution is usually effective. Why is this? I never >had the problem before I blew my power supply, and had to replace the analog >board. Can anybody suggest a possible solution (or a reason why this problem >would suddenly crop up, for that matter)? I also am interested in a solution to this one! My home Mac will (sometimes) suddenly take up this squeal (I assume 15.5kHz) after a half hour of silent running. Of course, when I attempt to run it without the case so that I can identify the offender, it never heats up enough to start this up. Unfortunately for me the "sharp rasp" doesn't work - or I'm not willing to "rasp" it sharp enough as I paid for it myself - it isn't the company's! Does anybody know where to start looking? Or should I just leave it on for a long period unattended, and after it fries have the analog board replaced! Ahem. -Brian Diehm Tektronix, Inc.
davidl@teklds.UUCP (David Levine) (01/16/86)
In article <1115@oddjob.UUCP> paluzzi@oddjob.UUCP (Greg Hajek) writes: >In article <251@birtch.UUCP> oleg@birtch.UUCP (Oleg Kiselev) writes: >>> I've never encountered a TV receiver or monitor that >>>didn't emit an annoying high pitched squeal at at least a >>>low audible level. >> ... Sometimes a sharp rasp on the side of the terminal would silence >>it for an hour or so ( and many people got so irritated by the squeal they >>did it routinely). > >I have had the same problem with my Mac, and also found that the "sharp rasp" >(read: "swift kick") solution is usually effective. Why is this? I never >had the problem before I blew my power supply, and had to replace the analog >board. Can anybody suggest a possible solution (or a reason why this problem >would suddenly crop up, for that matter)? I, too, can hear "ultrasonic" frequencies. Those ultrasonic motion detectors they use in some stores drive me just BATS. Fortunately, my Mac doesn't make those noises, for which I am grateful. The reason TVs and monitors squeal is this: A transformer is a stack of iron plates, separated from each other by a thin coat of lacquer or plastic, bound around with two or three wires. Alternating current flows through one wire, causing magnetic resonances in the iron plates, which in turn causes current to flow in another wire or wires. The ratio of the number of turns in the supplying wire to the number of turns in the receiving wire determines the ratio of output current to output voltage for a given input current and voltage. That's how a transformer turns one flavor of electricity into another. When the current flows, it causes magnetic stress in the iron plates. They attract and repel each other many times per second. If the lacquer is flexible or cracked, the plates actually move a tiny bit. If they rub against each other or any part of the case, this movement can cause a squeak or squeal. It's only obnoxious when the squeal is in audible frequencies. As it happens, the flyback transformer of a television or monitor (which controls how often the scanning dot on the screen "flies back" to the left edge after scanning across a line) uses frequencies that are audible to some of us. If you happen to have a transformer that squeals, and you can hear it, the device makes an annoying noise. Otherwise, it doesn't. Some transformers always squeal, others never do, others sometimes do and sometimes don't. If banging on the case helps, it's because it settles the plates into a configuration where they don't rub against each other. However, eventually they work their way into a configuration where they squeal again. There's no long-term solution except to replace the transformer with one that doesn't squeal (you might have to test a few at the frequency the Mac uses before you find one). Alternatively, you could attend a few Quiet Riot or Twisted Sister concerts to eliminate your ability to hear high frequencies... :-) Another modern Just-So Story from David D. Levine (...{decvax,ihnp4,hplabs}!tektronix!teklds!davidl) [UUCP] (davidl%teklds%tektronix@csnet-relay.arpa) [ARPA]
bart@reed.UUCP (Bart Massey) (01/18/86)
> (To net.micro.mac readers: this has been an ongoing discussion in net.audio, > but as this posting is a bit of a digression from audio talk, I have directed > followups to n.s.m.) > > In article <251@birtch.UUCP> oleg@birtch.UUCP (Oleg Kiselev) writes: > >> I've never encountered a TV receiver or monitor that > >>didn't emit an annoying high pitched squeal at at least a > >>low audible level. > > > >I have heard it is usually the vibration of transformers and/or capacitors > >(fly-back transformer?????). THe worst offenders I have heard were > >tvi925 . Sometimes a sharp rasp on the side of the terminal would silence > >it for an hour or so ( and many people got so irritated by the squeal they > >did it routinely). > > I have had the same problem with my Mac, and also found that the "sharp rasp" > (read: "swift kick") solution is usually effective. Why is this? I never > had the problem before I blew my power supply, and had to replace the analog > board. Can anybody suggest a possible solution (or a reason why this problem > would suddenly crop up, for that matter)? > My old high school electronics teacher said that it is in fact the flyback transformer vibrating (which makes sense) after it has worked a little loose from its mounting bracket. He claims he'd fixed many of them by shimming them with pieces of toothpick. WARNING: THIS IS A HIGH VOLTAGE AREA!! DO NOT TRY THIS UNLESS YOU KNOW EXACTLY WHAT YOU ARE DOING!!! I WILL NOT BE RESPONSIBLE FOR YOUR ELECTROCUTION!! Bart Massey ..tektronix!reed!bart
bill@crystal.UUCP (Bill Cox) (01/19/86)
> >I have had the same problem with my Mac, and also found that the "sharp rasp" > >(read: "swift kick") solution is usually effective. Why is this? I never > >had the problem before I blew my power supply, and had to replace the analog > >board. Can anybody suggest a possible solution (or a reason why this problem > >would suddenly crop up, for that matter)? > > I also am interested in a solution to this one! My home Mac will (sometimes) > suddenly take up this squeal (I assume 15.5kHz) after a half hour of silent > running. Of course, when I attempt to run it without the case so that I can > identify the offender, it never heats up enough to start this up. My mac is now on its third analog board. My original problem was that the left edge of the screen bowed in when text was highlighted (you could see a "dogleg" effect, around 5 screen pixels). Diagnosis: bad analog board; replaced. After replacement, there was a LOUD whistle, either a high flyback whine or something else (arcing?). Noise disappeared when the disk drives ran. It was so bad that I had to wear hearing protectors while using it. The newer analog boards have a silicone anode cap (that fits on the CRT), whereas my old one had a black rubber(?) one. A non-[electrically]conductive silicone grease on the silicone cap reduced the noise considerably. Apple's technical people told my dealer that either (1) a line filter/surge arrestor should be used; (2) the anode cap should be relubricated; or (3) replace the analog board. In my case, I use (1), (2) didn't do any more good, and the analog board died when the HV adjustments were tried. CAUTION: If you attempt the lubrication, KNOW WHAT YOU ARE DOING ! ! ! The voltage at the anode cap could KILL YOU ! ! ! I assume NO responsibility whatsoever for any use of this information. bill cox -- William Cox Computer Sciences Department University of Wisconsin, Madison WI bill@wisc.crys.edu ...{ihnp4,seismo,allegra}!uwvax!bill