Voltage Overdriven video signal from Sega Genesis to Narmi board

kipper2k · 01 July 2010, 03:56

Hi All,

I am playing around with the Sega Genesis 1 driving the video output through a custom cable to the Narmi Svideo board using R,G,B, CSync, Ground, and 5v.

It looks like the colours are being overdriven, i say this as i measure between 1.9v - 2.4v on all of the R,G and B inputs. In contrast when using the Amiga with the Narmi the output is anywhere between 0.6v and 0.950v

My question is assuming that the signal is too high what needs to be done in order to drive it down, the Narmi has the 75ohm resistor on each signal going to ground, does that need to be lowered or should a different RC value need to be used.

Any help greatly appreciated,

Thanks all

Zetr0 · 01 July 2010, 13:58

@Kipper2k

If I am not mistaken my friend, I believe that the Sega Genesis/Megadrive has a CXA1145 RGB encoder for the Composite / RF unit (same as the A600/A1200), you should be able to take the C/Y feed from that and just amplify it with a couple of transistors - 2n309 for each channel off the top of my head.

hope that helps =)

Hewitson · 02 July 2010, 05:24

Zetr0 is right.

http://www.jamma-nation-x.com/jammax/genesismods.html

Anyone tried this on the Amiga?

kipper2k · 02 July 2010, 14:33

@Hewitson,

Thanks for the info, i've seen a few mods you can do to the video chip but what i am trying to do is to be able to use the default output of both Genesis' using the RGB and Csync.

Both Genesis' look like they have the required output in order to be fed into the Narmi so my hope is to make a custom cable that people can use to plug their Genesis directly into the Narmi (and the Component vid mod i am working on) without opening up the Genesis itself. I think a lot of people do not want to open up their Genesis, etc.

I have the Dreamcast custom cable almost working, picture's too dark so that needs some tweaking.

Hewitson · 04 July 2010, 06:31

Thats fair enough.

Don't forget to include a headphone connector for stereo sound. The cable for the original Genesis will also be suitable for the Neo Geo AES.

kipper2k · 04 July 2010, 17:59

heres the pinouts i gleaned so far. Most of the 15 pins will be used dependent on the console attached

01 July 2010, 03:56	#1
kipper2k Registered User Join Date: Sep 2006 Location: Thunder Bay, Canada Posts: 4,323	Voltage Overdriven video signal from Sega Genesis to Narmi board Hi All, I am playing around with the Sega Genesis 1 driving the video output through a custom cable to the Narmi Svideo board using R,G,B, CSync, Ground, and 5v. It looks like the colours are being overdriven, i say this as i measure between 1.9v - 2.4v on all of the R,G and B inputs. In contrast when using the Amiga with the Narmi the output is anywhere between 0.6v and 0.950v My question is assuming that the signal is too high what needs to be done in order to drive it down, the Narmi has the 75ohm resistor on each signal going to ground, does that need to be lowered or should a different RC value need to be used. Any help greatly appreciated, Thanks all

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Sega gamepad only giving DOWN signal	Lord Aga	Hardware mods	6	09 June 2013 21:29
Alice Chip Sync Signal Voltage??	Ami_GFX	Hardware mods	5	25 September 2011 02:32
Using Narmi Video adapter on the Dreamcast	kipper2k	Hardware pics	6	27 October 2009 17:54
Sega Genesis: Honey Bee SG-18 end SG-6	Dexther	support.Hardware	2	22 September 2008 20:58
Pier Solar - A new Sega Genesis RPG	Retro-Nerd	Retrogaming General Discussion	15	07 September 2008 11:53

01 July 2010, 13:58	#2
Zetr0 Ya' like it Retr0? Join Date: Jul 2005 Location: United Kingdom Age: 49 Posts: 9,768	@Kipper2k If I am not mistaken my friend, I believe that the Sega Genesis/Megadrive has a CXA1145 RGB encoder for the Composite / RF unit (same as the A600/A1200), you should be able to take the C/Y feed from that and just amplify it with a couple of transistors - 2n309 for each channel off the top of my head. hope that helps =)

02 July 2010, 05:24	#3
Hewitson Registered User Join Date: Feb 2007 Location: Melbourne, Australia Age: 41 Posts: 3,773	Zetr0 is right. http://www.jamma-nation-x.com/jammax/genesismods.html Anyone tried this on the Amiga?

02 July 2010, 14:33	#4
kipper2k Registered User Join Date: Sep 2006 Location: Thunder Bay, Canada Posts: 4,323	@Hewitson, Thanks for the info, i've seen a few mods you can do to the video chip but what i am trying to do is to be able to use the default output of both Genesis' using the RGB and Csync. Both Genesis' look like they have the required output in order to be fed into the Narmi so my hope is to make a custom cable that people can use to plug their Genesis directly into the Narmi (and the Component vid mod i am working on) without opening up the Genesis itself. I think a lot of people do not want to open up their Genesis, etc. I have the Dreamcast custom cable almost working, picture's too dark so that needs some tweaking.

04 July 2010, 06:31	#5
Hewitson Registered User Join Date: Feb 2007 Location: Melbourne, Australia Age: 41 Posts: 3,773	Thats fair enough. Don't forget to include a headphone connector for stereo sound. The cable for the original Genesis will also be suitable for the Neo Geo AES.

04 July 2010, 17:59	#6
kipper2k Registered User Join Date: Sep 2006 Location: Thunder Bay, Canada Posts: 4,323	heres the pinouts i gleaned so far. Most of the 15 pins will be used dependent on the console attached

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)