Hello dear MSX fans,
The idea of creating a converter for connecting vintage computers to modern VGA monitors is not new. There are plenty of such projects on Internet. However, most of them are made for specific hardware, for example for Amiga. It's impossible to connect most of MSX computers to such converter without splitting the synchronization signal first. My idea is to create a universal converter that supports PAL and NTSC and that could be used for any vintage computer that has R, G, B and either composite or separate (horizontal+vertical) synchronization signals. The output from such converter is a high quality S-Video signal, that can be easily converted to VGA with a cheap 15 euro Chinese-made Video-to-VGA converter. The quality of composite video is acceptable, but nothing compared to S-Video.
So, the prototype based on AD724 chip is now ready and is working fine. I called this device "Zefisha" (don't ask why and what this means). The quality of S-Video output is indeed great, PAL and NTSC seems to work correctly, both sync signal types are supported. There's a switch that allows to chose either composite or separate sync signals. The standard 15-pin VGA female connectors are used for input, the output has RCA and S-Video connectors. In order to connect a vintage computer to the converter, you have to make a special cable from computer's RGB port to the male VGA connector. The pinout for the VGA connector matches the real VGA's pinout for convenience.
I tested the converter with Yamaha YIS805 and YIS503, Panasonic FS-A1, Sony F1-XV and Amiga 500. The Atari ST 1040, Commodore C64 and C64C, Sinclair ZX Spectrum +3 will be tested next - as soon as I make the special cables for them. You can see the photos of the assembling process as well as the future circuit board pictures here:
http://www.finnov.net/~wierzbowsky/zefisha
The original plan was to use the EL1883 chip to split composite signals, but this failed for unknown reason. And due to the lack of the oscilloscope I could not diagnose the problem. So I decided to use the good old EL1881 chip in a DIP case instead. For making connections between components I used the "wiring pen" for the first time. Seems to work just fine as long as your soldering iron's temperature is above 400 C. Be advised that using such pen is recommended only in properly ventilated areas as some gas is emitted when you solder the wire.
I will order several circuit boards for the convertor soon and the next prototype will be assembled on proper board. The board is designed to support both AD724 and AD725 chips. For AD725 you can install an optional Chroma filter. For AD724 you will need to solder a wire to AD72x chip's pin 12 (Select). The wire should be connected to power for 4FSC mode (14,3 and 17,7 mHz) or to be connected to the ground for the FSC mode (3,5 and 4,5 mHz). The potentiometers are installed on R, G, B and Composite video lines to adjust the signal levels. The selection between PAL and NTSC is possible with 2 jumpers. If you wish, you can use one oscillator only for either PAL or NTSC format and you will need to set the jumpers correctly.
So if you have questions about this project or you will be willing to purchase the board or the assembled converter, feel free to contact me. I am not going to charge 80-130 euro for such device like some MSX hardware makers do. I believe that it's unethical to make business on people's nostalgia for the old 8-bit computers. But I am not reproaching those guys in any way - they can sell their hardware for whatever price they feel right...
Alexey
