" bravely wrote to "All" (14 Jul 05 08:58:37)
--- on the heady topic of "CRT image shrinks and grows with changes to
brightness"

da From:
da Xref: aeinews sci.electronics.repair:53191

da I have a 7-year-old 15" CRT monitor that is connected to a standard
da PC. Lately I noticed that the size of the monitor's onscreen image is
da affected by changes to the image's brightness (the brighter the
da wider).
da For example, my Desktop background is dark. If I click to maximize a
da white window, the onscreen image expands by (approximately) 1mm on
da every border. If I then click to minimize the window, restoring the
da dark Desktop, the image contracts to its previous state. The same
da occurs when the monitor's Contrast control is quickly rotated from one
da end to the other.

da Is this behavior normal or a sign of a dirty or aged CRT? And speaking
da old CRTs, would it be wise, with respect to health or sight risks, to
da continue to use this monitor as long as it's operating properly (as
da the average user would say)?

Dave

It might be a B+ voltage regulation problem. However, a weak CRT could
also cause the picture size to change. Normally the HV tracks the
average beam current so that as a result the size stays the same (HV
derived vertical supply). But when CRT emission drops enough the
tracking is lost and this shows up as effects in pix size (both horz &
vert). Test the crt emission to be sure.

A*s*i*m*o*v

.... High voltage can give a dangerously uncomfortable discharge.