I should have gone into more detail about my explanation. The offending lamp didn't actually damage the monitors but caused the disturbance. After replacing 2 monitors (which were OK in another location), I got suspicious and unplugged the lamp and voila! the jittering disappeared. This lamp was not used (no bulb in it ) but was turned on. I hope this clears things up a bit. This problem also has occurred in some mobile test stands we built which had a blower motor near the monitor (relocated the blower motor). Regards, Fred Hahnel ISO9000 Point Person PFSL > From: Mark Rode [SMTP:[log in to unmask]] snip > however this is the first > time I have heard of a ballast actually damaging a monitor. A halogen > light > does not require a transformer although a twelve volt transformer is often > used for energy efficiency. > It is always a good idea to keep any devices that produce a magnetic > fields > a foot or so away from your monitor to avoid picture distortion. > Mark > > >Be sure no fluorescent or halogen lights are nearby either. They use > >transformers which will mess up a monitor. I had two monitors replaced > at > >work because of a fluorescent lamp that was on (without a bulb in it > yet!!) > >and it made the monitor jittery. > >Fred Hahnel > > > > >>I have a problem with a Princeton Graphic Systems EO70 17" > monitor.Actually, > >> >I am not totally sure it is the monitor. Sometimes -- not all the time > -- > >> >after operating for several hours, the display begins to jitter. It > >>> >Bryan S. Tyson