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9.13) Picture size changing
 
 
If the picture area is expanding or contracting without any changes to your
video card settings or other software. then there is a problem with the power
supplies in the monitor.  This would be confirmed if the change is (1) gradual
over the course of say, an hour, and/or (2) gently whacking the monitor has
some effect indicating bad internal connections.  Software problems would not
result in either of these characteristics.
 
Note that if the change is very small - say, less than 1 or 2%, then it may
simply be normal for your monitor due to poor design or the use of inferior
components - some parts associated with power supply regulation may be
changing value as the monitors warms up.
 
A way to confirm that something is drifting due to thermal problems would
be the monitor from another computer and see if the same thing happens.
Just powering the monitor by itself (but not in any power saving mode) might
also work for this test.
 
One possible cause could be that the high voltage is drifting gradually
due to a faulty component - increasing and making the beam 'stiffer' or
vice-versa.  If this is the case there might also be a gradual change in
brightness as well (decreasing image size -> increase in brightness).
Alternatively, the HV may be stable but the power to both H and V deflection
is gradually changing.
 
Excess high voltage can increase the X-ray emissions and any kind of power
supply problems may ultimately result in total failure and an expensive
repair.  Therefore, these symptoms should not be ignored.  See the sections
on low voltage and high voltage power supply problems.