NAOMI VGA (LOW RES SETTING) TO ARCADE STANDARD MONITOR

OldFoo · Post by **OldFoo** » Mon Sep 28, 2009 1:14 pm

Quick question, are you supplying power to the Sega I/O? If MKL is correct, this may explain why your monitor is dim. Another thing to check is if you look in the Test mode, I remember there being an adjustment for the video output. One is the standard .7v p-p and the other I can't remember at the moment. Changing this might help if all else fails.

OldFoo · Post by **OldFoo** » Mon Sep 28, 2009 1:42 pm

Thanks for your reply..

I do not supply additional power to the I/O other than the power coming from the JAMMA harness. I cannot find the setting you mention in the test menus..?

OldFoo · Post by **OldFoo** » Mon Sep 28, 2009 1:55 pm

I found a reference table comparing the SEGA I/O to the CAPCOM I/O, stating that the SEGA I/O does not amplify RGB. It is on this page:

http://cc.arkadtorget.se/naomi.html#capcom_converter

OldFoo · Post by **OldFoo** » Mon Sep 28, 2009 3:15 pm

When you're not in the condition to judge things for yourself you clutch at whatever info you can find and you found that page but unfortunately there is no in-depth hardware analysis there so you cannot know if the author made a typo or he actually means it. You should ask yourself (or the people that deny the presence of an RGB amp on the Sega I/O) a few questions though:

- if the Sega I/O doesn't have an RGB amp, then what is the function of that circuit shown in the closeup pic I posted above?

- if the Sega I/O doesn't have an RGB amp and requires one, then why is it supposed to plug into a Jamma harness?

- if an RGB amp is required, how come there is no official Sega part # as for the audio power amp?

OldFoo · Post by **OldFoo** » Mon Sep 28, 2009 3:28 pm

I've also read that there are other uses for the 74F86 you mentioned. I'm not saying it's wrong, just unconfirmed from my end. The IC in questions is, for the most part, a set of logic gates. I'll have to check this out. :smt033

OldFoo · Post by **OldFoo** » Mon Sep 28, 2009 6:43 pm

MKL wrote:When you're not in the condition to judge things for yourself you clutch at whatever info you can find

True. I did not post the page to prove you were wrong; just as an additional piece of information I found. There is not much info on the Sega I/O, so all is welcome, imo.

He might be right, you might be right. I know I am right about the dimness of my display

OldFoo · Post by **OldFoo** » Thu Oct 01, 2009 8:37 pm

joshua3dg wrote:I've also read that there are other uses for the 74F86 you mentioned. I'm not saying it's wrong, just unconfirmed from my end. The IC in questions is, for the most part, a set of logic gates. I'll have to check this out. :smt033

You should be able to easily figure this out by running continuity tests between the chip and the H/V sync pins on the HD-15 connector for the VGA cable... Then testing the continuity between pins on the chip and the JAMMA edge sync connection.

RJ

OldFoo · Post by **OldFoo** » Mon Nov 16, 2009 6:43 pm

Cageman wrote:Hmm... ok..

Yeah, I tried fiddling around with them, but the monitor is set up perfectly for JAMMA PCBs. MVS also runs fine. It is only with the NAOMI that the picture becomes dim.. So I actually do not want to constantly change the RGB gains when swapping systems..

I had a dim picture only when I hooked up my Naomi mobo to my JAMMA cab and then realized that the picture would get brighter if I separately grounded the sound amp (weird I know). It turned out that the trace for the video ground on the mobo filter board was burned. Ken of Advanced Repair Center walked me through jumping the trace and voila, it works great now. He told me this was a common problem with the Naomi filter boards so I hope the info helps.