Testing VGA to TV drivers without hardware
Before buying the components for VGA to TV converter circuit and take trouble in building it, it might be a good idea to test if the drivers work nicely with the computer system you have. If you happen to have a frequency counter or an oscilloscope you can make quite good compatibility tests without building the actual converter circuit.
- Load the VGA to TV driver. Put it to the TV mode (most drivers go to TV disolat mode when loaded)
- If your monitor looses sync, then contirnue testing. If you still see the picture on regular VGA monitor the driver did not work correctly (NOTE: The picture might sill be visible after driver loading on some old multisync monitors capable os syncing doe to 15 kHz horizonal rate).
- Disconnect the monitor.
- Connect the ground of your measuring equipment input to the PC case.
- Connect the measuring equipment signal input to VGA HSYNC pin (pin 13). You should be able to measure around 15.6-15.8 kHz frequency or around 63-64 microsecond time between the sync pulses. If you get something ant higher frequency the driver does not work correctly.
- Connect the measuring equipment signal input to VGA VSYNC pin (pin 14). You should be able to measure around 50 or 60 Hz frequency (time between sync pulses around 20 or 16.6 milliseconds).
- If everythign went nicely to here, then at least this one graphics mode is expected to work woth VGA to TV converter circuit. This simple measurement does not 100% guarantee that everythign is correct, but iges quite good confidence. You can trst also other screen modes using the same measurement methods.
Tomi Engdahl <Tomi.Engdahl@iki.fi>