Going to hook a Genesis up to a monitor. Need some details confirmed please.

Started by Rom Zito, March 09, 2011, 04:28:23 AM

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Rom Zito

I have Model 1 and 2 Genesis's with scart cables.  Using a RGB>YUV converter I have been playing them on a Sony CRT TV without issue.  But now I want to move up to an arcade monitor.

I've arranged a purchase of a 27" monitor, JAMMA harness, and power supply, and I'll be picking it all up in a few days.  My plan was to simply tap the RGB, sync, and ground leads from the end of the scart cable and feed that to the monitor.

Since I've never actually worked with such a setup before, there are several details that I am less than confident on, so while I still have a few days to prepare I was hoping this forum could ease some of my worries.

Will the capacitors installed in my scart cables cause image problems if left in line to the monitor?  The caps are there to adjust color for a scart TV, which is much like an arcade monitor I thought, but I don't know for certain if they would be a problem.

Is the genesis sync signal compatible with the monitor?  I thought I read here that it would be, as it is a composite H+V sync signal, but does not carry video, so it would not need to be split or cleaned for a monitor to use. But then I saw this video and it got me worried.
Genesis connected to my Arcade Monitor
What could have gone wrong here?

Do I have to feed the video signal into a JAMMA harness to get it to the monitor?  I assumed that I'd tap my leads from the scart cable to the monitor's board and not need a harness.  However I've been told I need the harness to power this monitor, so maybe the video should go through it as well?

This monitor should be a 15k "low" resolution arcade monitor.  My internet research had led me to believe that I could feed it RGB input from any classic game system and it would resolve itself, but, once again, I've no practical experience so that's another point that that I need reassurance on.

Thanks for reading and for any information you can give me to confirm these details that I'm unsure of.


So here we have an issue with the Mega Drive design.

The Mega Drive uses an CXA1145 RGB to composite video encoder chip which contains built in RGB buffer with DC level restoration capability (aka clamper). For the clamper circuit (the clamper actually short the three video signal lines to the GND for a brief moment at an certain time of the sync cycle) to work properly the sync signal must be present on the CXA chip input.

And the sync level (voltage range) is critical for the CXA chip proper operation. The issue is that the VDP signal output is thrown to the A/V connector staight, without any buffering. So if your monitor has a low impedance sync input the CXA chip will lose the proper reference for the clamping and it will start to disrupt the video signal. All outputs will stop working properly as it will also affect the composite video output.

The suggested fix is use the (already amplified) output the CXA chip offers:

This thread has a good read on that problem and detailed information on the fix.    :)


have a chat to rgb32e on here, he's built a scart to jamma adaptor which has its own video amp and will take just about any 15khz rgb signal and correct it for use with an arcade monitor. it even has an audio amp in it so you can use your arcade speakers without messing around with a hack job amplifier.

you'll find that without a video amp even once you fix the sync issue the picture will look all washed out because arcade rgb has a higher peak voltage.

I think he's selling the converters for around $50. I've got one and it's excellent. I've been playing my xbox 360 on my 80's lowboy:D