How do I get Brightness up

I aquired a hardly used HP A4033A monitor. I bought the necessary BNC to VGA cable, and the monitor works well with the exeption that there it could use some more brightness even when the user brightness control is set to maximum. Being an old TV repair guy, removed the plastic and aluminum covers to look for an internal brightness adjustment, but could not find any. Does anyone know how I can get the brightness up and/or adjust the individual RGB gun brightnesses?

Hal Netkin