SCART (RGBHV@15Khz) to VGA Adaptors

Hello Everybody,

According to several schematics at various websites;

Its possible to split the scan synchronization signal from a (SCART compatible) video source (anything RGB + Composite synch at 15Khz)
into a 'near' VGA standard - enough that some VGA computer monitors (CRT mostly) can display it directly.

The usual component is the LM1881 synch separator chip.

What is unclear is what usually can go wrong with this; e.g. different logic levels, AC biased vs. DC signal, and so on.

Has anyone actually built these kinds of converters before?

Any suggestions ?

 

Most of these circuits are generally for machines that can output a 31.5Khz signal via SCART or a VGA monitor or projector that can accept a 15Khz signal (for example a tri sync monitor). All they do is strip the H and V syncs from the composite sync and change the 0.7Vpp to a 5Vpp signal from SCART to VGA. They do however not upscale the signal so you are not going to magically get a picture from a 15Khz signal on a 31.5Khz monitor.

What you need is an upscaler and these tend not to be circuits, you can buy a RGB to VGA convertor board for around $40/$50 (just search Arcade VGA convertor), you will need a tiny circuit to strip Composite to H/V sync but this will cost under $5, you can find more details here including a nice scanline mod too.. http://www.mmmonkey.co.uk/console/other/rgb2vga.htm

 

I've got 2 of the chips for doing this, tried it from GC -> VGA LCD but it didn't work because the LCD won't accept 15Khz but yeah generally CRTs work.