jeff@cjsa.WA.COM (Jeffery Small) (01/17/89)
This is a request for help from some of you UNIX-PC hardware gurus out there. I have three 3B1 machines which were recently relocated to a new site. On two of these machines, I am now experiencing "screen wave" - a distortion in the display which looks like a wave running across the screen. The frequency which I observe this condition has been increasing and now I experience this every few minutes typically. The power at this new site is not as clean as my previous location and I occasionally see dimming of the lights. I have always been impressed with the stability of the power supply in this unit and I am experiencing no operational problems (other than the screen wave) with any of them - even when I measure a significant voltage drop on the line. However, the wavy screen does not correspond to the power fluctuations which my eyes register (from observing the lights). In fact, I've never been able to observe ANY screen wave at the same time I saw the lights dim and I can't watch both screens at the same time to see if the condition occurs in sync. I put an analog volt-ohm meter on the line and am getting about 116-117 VAC and I see no variation in the voltage during periods when the screen waves - but possibly the meter is not responsive enough to register rapid fluctuations? So, on to my question: Does anyone have any past experience with this condition which would indicate whether the the problem is most likely with the external power (and I need some line conditioning) or might possibly be a dying component (power supply, capacitor, etc) which has proven in the past to be the cause of this type of problem and should be checked/replaced? Any help, hints or suggestions will be greatly appreciated. -- Jeffery Small (206) 485-5596 uw-beaver!uw-nsr!uw-warp C. Jeffery Small and Associates !cjsa!jeff 19112 152nd Ave NE - Woodinville, WA 98072 uunet!nwnexus
gil@limbic.UUCP (Gil Kloepfer Jr.) (01/19/89)
In article <169@cjsa.WA.COM> jeff@cjsa.WA.COM (Jeffery Small) writes: >I have three 3B1 machines which were recently relocated to a new site. On two >of these machines, I am now experiencing "screen wave" - a distortion in the >display which looks like a wave running across the screen. The frequency >which I observe this condition has been increasing and now I experience this >every few minutes typically. This can happen if the back of the two displays are too close to one another, or if another monitor or electromagnetic-based device is close to the display. Try moving the units a little further away from each other, or away from a potiential source of electromagnetism (like a TV set or the like). I've seen the same phenomena on a VAXstation monitor when a VT220 terminal is on and next to the monitor. ------ Gil Kloepfer, Jr. U-Net: {decuac,boulder,talcott,sbcs}!icus!limbic!gil ICUS Software Systems Voice: (516) 968-6860 [H] (516) 746-2350 x219 [W] P.O. Box 1 Internet: gil@icus.islp.ny.us Islip Terrace, NY 11752 "Life's a ... well, you know..."
jbm@uncle.UUCP (John B. Milton) (01/20/89)
In article <169@cjsa.WA.COM> jeff@cjsa.WA.COM (Jeffery Small) writes: >This is a request for help from some of you UNIX-PC hardware gurus out there. > >I have three 3B1 machines which were recently relocated to a new site. On two >of these machines, I am now experiencing "screen wave" - a distortion in the >display which looks like a wave running across the screen. The frequency >which I observe this condition has been increasing and now I experience this >every few minutes typically. This does not sound like the dirty pots problem, and no, I'm not talking about bathroom hygiene. I'm talking about the variable resistors in the monitor. If you take the back off the monitor (two screws), they're on the PC board poking out the back. The symptom that goes alon with these is "jumping", not "waving". The procedure for the jumpies is to turn each pot back and forth a couple of times, then BACK TO WHERE IT WAS. This cleans off oxides that build up on wiper. DANGER!! WARNING!! There is 14,000 volts in there! It may sound stupid, but Wavies are usually caused by the screen refresh rate being out of sync with the 60Hz line and the power supply being weak. If this is what's going on, then the rate of wavies will change over the day as the line frequency shifts. For those of you who don't know: during high load periods on the power grid, the line frequency drops below 60 Hz by a little bit. This means that all clocks based on the 60Hz line run slow during the day. To fix this, the electric utilties run the grid a little over 60 Hz at night, so you clocks catch up and do not loose time. They run a little slow during the day, a little fast at night. Since the wavies are caused by slight difference in the screen refresh rate and the grid, the rate of the wave being the difference, this rate will be different at different times of the day. If that's the problem. A related problem (stupid as it sounds) could be the lighting. If the systems were moved into a flourecent lit environment, the same reason I just described could be cause the screen to APPEAR to flicker. I wonder if the one system that does not have the wavies is facing a window? Hmm. John -- John Bly Milton IV, jbm@uncle.UUCP, n8emr!uncle!jbm@osu-cis.cis.ohio-state.edu (614) h:294-4823, w:764-2933; Got any good 74LS503 circuits?
toml@rob.UUCP ( Tom Luteran ) (01/21/89)
In article <428@limbic.UUCP>, gil@limbic.UUCP (Gil Kloepfer Jr.) writes: > In article <169@cjsa.WA.COM> jeff@cjsa.WA.COM (Jeffery Small) writes: > >I have three 3B1 machines which were recently relocated to a new site. On two > >of these machines, I am now experiencing "screen wave" - a distortion in the > >display which looks like a wave running across the screen. The frequency > >which I observe this condition has been increasing and now I experience this > >every few minutes typically. > > This can happen if the back of the two displays are too close to one > another, or if another monitor or electromagnetic-based device is close > to the display. ... There's a Macintosh in our training room that exhibits the same distortion. We found out that this was from the fluorescent lights in the room, one of which was located directly above the Mac. We haven't come up with a solution yet, although I doubt we'll replace the lights with incandescants! Tom Luteran uunet!rob!toml Merck Sharp & Dohme Research Labs (201) 594-7288 P.O.Box 2000 Rahway, NJ 07065-0900