JAMMA Video Output To VGA Monitor

[Majoraslayer64]

This isn't completely related to making a MAME cabinet, but the people here seem to be the most likely to be able to answer this question.  So, here it goes.

I'm working on an old arcade machine in which the original monitor has.....well, exploded. So what I would like to do in order to cut down the cost of replacing the monitor with another arcade monitor is to make an adapter that allows for a standard monitor with a VGA connector to be used.

Now, I've done some research and found that the video signal sent from the JAMMA board consists of RGB and a syncronization signal that is compatible with NTSC standards (50-60Hz). The RGB and sync signals have their own unique wires, so splitting them off for VGA connection won't be a problem.

RGB is easy, however a standard VGA monitor has two sync signals (HSYNC and VSYNC) instead of just one. The vertical sync signal is equal to the sync signal being output (50-60Hz), but the HSYNC is roughly twice the VSYNC.

I've tried this project once before by connecting the sync signal to both the horizontal and vertical sync inputs to the monitor. The colors correctly appeared on the monitor, but the image was distorted horizontally.

I was wondering, and I was hoping someone here might know, are the VSYNC and HSYNC signals regular analog clock pulses (i.e. a repeating pattern), or do they depend on the image being sent to the monitor?

The monitor I'll be using has the BNC connections in the back, so it is easy to split R, G, B, HSYNC, and VSYNC. If the sync signals are a repeating pattern, then I should be able to test it out by connecting the sync signals from my computer output to the monitor, and the RGB from the JAMMA board to get it to display correctly. If this does work, I'll also need to know how I might double the frequency of the sync signal (its easy to split off into two).

Any help anyone can provide would be very much appreciated.

[grantspain]

unless that vga monitor has a 15khz input it will not work on jamma cabs,the only way you could do it is buy a 15k to 31k converter
your best  bet is to repair the original monitor or get a replacement chassis(something like a wei ya) all depending if the old tube is good

[BobA]

Sounds like you already have PC to Jamma video worked out so put a TV in the old cab and use a JROK jamma to TV converter to convert the signal.  Cheaper than VGA and a converter.