[GreenKeys] minor trouble with Info-tech M600

[Eugene Hertz]

Hi all, anyone have one of these? I have a strang problem where the video output is not consistent from the top of the screen to the bottom. The background on the top is brighter than the bottom. Therefore when the text scrolls to the top, it tends to disappear. The bottom of the screen is fine (or i can adjust the monitor so the top is ok, but text at the bottom goes to black)

I have a schematic, but seems to have very little analog circuitry for the video section (I was at least hoping for a pot!) Any one know if an RC was off somehow if the response of an off RC could cause this kind of background gradient? 

Thanks
Eugene