"N_Cook" wrote in message ...

I had tried dropping back to 16 bit colour but the same "1 bit"
saturation effect on a test colour bar image. I also had another
rummage around for video settings but could only find display
settings of a x b and no Hz info.

There /has/ to be a "screen refresh rate" setting somewhere. The rate has to
be within the range a monitor can handle. This is particularly true for CRT
displays, which can be damaged by an excessively high rate.

I right-clicked the Windows 7 desktop, and selected "Screen Resolution". On
that screen, I clicked "Advanced settings". On the "Monitor" tab, you can
select the screen refresh rate.