Posted by rosborn on 30, 2001 at 9:20 PM:
In Reply to: TTL versus Video levels causing problems? posted by Matt on 30, 2001 at 9:33 AM:
: Another possability was raised by a TV technician I was speaking to. He says that VGA out from a video card runs at TTL voltage 0-0.5v? whereas TV and Arcade monitors take input at video voltage 0-1v. Thus what I am seeing could be a reduction in dynamic range (or low contrast I 'spose).
This is a guess for your problem, but it's easy to test and is worth a shot...
I've been searching for voltage specifics for VGA and analog RGB and have only found that analog RGB expects around 1V peak-to-peak as an input.
Here's something I would try for your case. Get some ceramic capacitors (the value isn't real important in this case, .1uF should work) and place them between your video card RGB outputs and the monitor (called coupling capacitors). This will eliminate any differences in the base voltage for the analog signal. For example: your monitor expects 1V peak-to-peak, but that may mean 5V-6V, or it could mean 50V-51V. What the capacitors will do is take the voltage variance your video card produces and pass it to the monitor at the voltage levels that it expects.
So what you need to do is just treat the three ceramic capacitors like small pieces of wire between your video card and the monitor for the R, G, and B leads (the signal will go into one leg of the capacitor and come out of the other).
Note: Make sure you get ceramic capacitors and not electrolytic ones.
I know some other people who read this board have some electronics backgrounds. Please add your thoughts.