Great comparison between Mega Drive - Genesis RGB output.

[MKL]

If it were an inherent problem of the CXA1145P then any device with this IC would exhibit the same issue but this does not seem to be the case: the Neo Geo has this encoder too and the jailbar problem is only present on one revision and can be fixed externally without cutting the oscillator trace.

[zak]

I have a Sega CDX hooked up to a BVM (RGB).

Genesis games look flawless on it. However, Sega CD games have a weird noise/interference effect.

Is this normal?

[FBX]

If it were an inherent problem of the CXA1145P then any device with this IC would exhibit the same issue but this does not seem to be the case: the Neo Geo has this encoder too and the jailbar problem is only present on one revision and can be fixed externally without cutting the oscillator trace.

Then it must be something about the Genesis subcarrier signal the CXA doesn't like. I've finished my toggle switch mod (and also installed stereo RCA jacks in the back of the console):







I can flick the toggle switch closed during gameplay, and the blue channel instantly gets jail bars. Flicking the switch open instantly removes the jail bars. Keep in mind of course I wouldn't put the switch up front like I have it on this console, but the console previously had a hole drilled in that spot many years ago, so I decided to make use of the hole for the toggle switch.

[Ryoandr]

If it were an inherent problem of the CXA1145P then any device with this IC would exhibit the same issue but this does not seem to be the case: the Neo Geo has this encoder too and the jailbar problem is only present on one revision and can be fixed externally without cutting the oscillator trace.

IIRC the Neogeo has a 3.57 crystal, the subcarrier isn't derived from the main oscillator. So if jailbars are present, they will scroll over and will be far less noticiable.

[FBX]

Update:

Did some PMs with one of the forum members where he lifted pin 6 on the CXA of his VA3 and got very little appreciable results. So we were thinking my results were so perfect looking because of the physical location where I sever the trace. As a min-max test of theory, he cut pin 50 on the VDP side and it instantly removed all visible trace of the jail bars. So it really does seem to be the case that the coupling is actually happening in the traces leading to the CXA chip rather than the CXA chip itself. Reviewing the photo of the board bottom on my VA2, you can see the 'B' channel is right next to the subcarrier line during a good chunk of the path, and where I sever the trace is well before the two run next to each other.

[Ashura]

This article sort of labels Japanese MDs as the bad eggs, however, since this is far from scientific, what are people's experiences here with them? Are there "good" Japanese models? I have an MD2 and unfortunately from what I remember it had fairly bad video and audio. The have 2 Genesis 2s and one of them has absolutely terrible audio, while the other is fine.

I also have a Wondermega and an Xeye. It's surprising the Xeye is the winner because outwardly it always felt cheap/like a piece of junk to me.

[Ryoandr]

pretty sure it's the same as Genesis.
VA0 to VA2 have slightly higher filtering but too loud amp (very noticiable on konami games), also IIRC VA0 has a bug with Landstalker.
VA3 to VA6.8 are pretty much the ones to get.
VA7 is horrible (Model 2 in Model 1 shell really)

Model 2 VA0 to VA1.8 have bad audio, VA2 and above have minor flaws but are more acceptable.

No idea bout Wondermega and X-eye.

[bateman82]

This article sort of labels Japanese MDs as the bad eggs, however, since this is far from scientific, what are people's experiences here with them? Are there "good" Japanese models? I have an MD2 and unfortunately from what I remember it had fairly bad video and audio. The have 2 Genesis 2s and one of them has absolutely terrible audio, while the other is fine.

I also have a Wondermega and an Xeye. It's surprising the Xeye is the winner because outwardly it always felt cheap/like a piece of junk to me.

I don't understand why complaining, if you want more accuracy you have a very long thread on Sega-16 forum (even if it's not tested by only one person, in the same enviroment etc... so it's far from scientific). Like FinalBaton wrote:
"It's still cool that these people did this test."

About the X'eye your opinion seems very far from scientific.
I quite like the shape of Wondermega 2 (the japanese X'eye), from an aesthetics point of view I will say:

1)Wondermega 1

2)Mega Drive 1 + Mega CD 1

3)Wondermega 2 (X'eye)

4)Mega Drive 2 + Mega CD 2

5)Pioneer Laseractive

6)Multi Mega (CdX, a boring portable cd player)

7)Aiwa Mega Cd (a ugly mini boombox)

[ApolloBoy]

6)Multi Mega (CdX, a boring portable cd player)

One that's also unreliable and a nightmare to fix BTW.

[Ashura]

I wasn't complaining about the article; it IS cool they did it. It's just that it seemed weird that MegaDrives performed so differently than the same Genesis models. Is there a link to the Sega16 thread? I'd read it.

My opinion on the X'eye is just what I feel. The first model Wondermega is just built so much better, and the plastic felt cheaper to me when I got the X'eye.

[AndehX]

My Japanese model 1 VA3 has jailbars pretty badly and lifting pin 6 of CXA does absolutely nothing. I'll try lifting pin 50 of the VDP sometime and see if that helps.

[Ryoandr]

My Japanese model 1 VA3 has jailbars pretty badly and lifting pin 6 of CXA does absolutely nothing. I'll try lifting pin 50 of the VDP sometime and see if that helps.

you have to lift and connect to ground CXA pin 6. Leaving it floating makes it an antenna.

[Blair]

My opinion on the X'eye is just what I feel. The first model Wondermega is just built so much better, and the plastic felt cheaper to me when I got the X'eye.

that makes sense, the Wondermega served as a high-end Mega Drive and Mega-CD unit, with built in S-Video and RCA audio output. four versions of the system were produced (some had Karaoke functions, others had Wireless controllers), although I've heard some (all?) of them don't support RGB without modification.

[FBX]

My Japanese model 1 VA3 has jailbars pretty badly and lifting pin 6 of CXA does absolutely nothing. I'll try lifting pin 50 of the VDP sometime and see if that helps.

It should based on what I'm hearing. It may very well be the coupling happens in the traces leading up to the CXA, which explains why I always get fantastic results because I cut the trace near the VDP.

[Voultar]

I made an image of the schematic of the CXA chip so you can see the physical location of where the coupling is happening:



As you can see, it doesn't matter where you cut the trace. Just so long as that oscillator can't receive the signal, so it won't couple into the blue channel.

This isn't necessarily the case.

[FBX]

This isn't necessarily the case.

Yeah it sort of got sussed when nakedarthur tried lifting pin 6 on his CXA and it didn't really work. Then he clipped pin 50 on the VDP side and it worked perfectly. So my guess is the coupling is happening in the traces leading up to the CXA rather than in the CXA itself. This explains why I was getting such great results cutting the trace on the VDP side.

[Voultar]

This isn't necessarily the case.

Yeah it sort of got sussed when nakedarthur tried lifting pin 6 on his CXA and it didn't really work. Then he clipped pin 50 on the VDP side and it worked perfectly. So my guess is the coupling is happening in the traces leading up to the CXA rather than in the CXA itself. This explains why I was getting such great results cutting the trace on the VDP side.

https://youtu.be/dsHjLco6VNY?t=50m11s

[FBX]

Yeah it sort of got sussed when nakedarthur tried lifting pin 6 on his CXA and it didn't really work. Then he clipped pin 50 on the VDP side and it worked perfectly. So my guess is the coupling is happening in the traces leading up to the CXA rather than in the CXA itself. This explains why I was getting such great results cutting the trace on the VDP side.

https://youtu.be/dsHjLco6VNY?t=50m11s

Lol nice! So it really was the trace lines after all. Going back and reviewing the photo I took of the underside of the VA2, you can actually see the blue channel is literally right next to that subcarrier trace line through most of the board, and where I cut the trace is well before they meet up. In my defense, I was 'told' it was the CXA chip by Youtube bloggers, and just assumed they knew what they were talking about. That's what I get for trusting youtubers.

[ASDR]

I just tried cutting the trace on my PAL VA4 MD. Didn't really have the desired effect. This is what it looks like before the mod:

https://imgur.com/a/4v8Tq

After, the jail bars look more regular than in the picture and the intensity of the bars seems to vary across the horizontal axis with a sine wave like pattern, if that makes sense.

Here's a picture, you can compare to the similar one from the above link:

https://imgur.com/a/gepHK

This looks far worse in person, though. I guess it's a little better compared to before? Certainly different. It really looks worst in Steel Empire, the color combination just seems to bring the jail bars out. Sonic 2 looks much better, certain screens like the one with the Sonic logo and blue background look almost perfect.

I cut the trace on the top side of the board before it goes into the via. The routing on the bottom of my board looked totally different than here:

http://www.firebrandx.com/downloads/sit ... ods-04.png

The pin 50 goes to quite a few different places, but eventually can be traced to pin 6 on the video encoder chip. I triple checked that I cut the right trace, used the pin markings on the board, counted thrice from both directions, checked again with the pinout from here http://md.squee.co/VDP#Pinout. I uses a continuity tester with one lead on pin 50 and the other making contact with the via through a short wrapping wire, seems to be severed clean. Lifting the pin was certainly far above my skill level.

Any ideas? Did I do something wrong? Do I just have the wrong MD model for this to work? Can I try something else?

Thanks

[FBX]

Those lines look like they might be caused by something else.

At any rate, I went OCD dork-out and made a new image illustrating the proximity of the RGB lines to the subcarrier signal on the VA2 Genesis:

Spoiler

For North American console owners of these early models, you can see what Voultar was describing on how the subcarrier runs right next to the blue trace of the RGB signals. I'm curious to know if an RGB bypass board would pretty much have to tie directly into pins 27, 28, and 29 in order to be effective, or if Voultar plans on a board that cleans out the interference and ties in elsewhere?

[ASDR]

Hm, I wish I knew what is causing these lines :/ I don't think an RGB bypass board would help me as the soldering required would likely be beyond my skill. Cutting that trace with <1mm room to maneuver was nerve-wrecking enough, I don't think I would manage to to desolder chip legs and hook up kynar wire to them.

For what it's worth, here's the area around the video encoder on my VA4 PAL MD board, looks rather different:

https://imgur.com/a/3yh1l

Any suggestions much appreciated, would love to have a clean picture from my MD

[FBX]

Yeah I just don't know with that revision what's going on there. I don't think it's the subcarrier because you're getting jail bars in all 3 channels from the looks of it, and your jail bar pattern looks quite different than mine did.

[ASDR]

Yeah, strange. Disconnecting the sub carrier certainly did something. Before I had this pattern were two jail bars are bunched up with some space around them, now it's more regular. This is not from my MD, but it now looks exactly like that:

https://imgur.com/a/QENR6

Notice that the bars seem to fade in and out with a sine wave like intensity along the horizontal axis, very apparent in the blue strip at the top.

Not sure what to do, maybe I just buy another Model 1 HDG MD and hope it's a VA2 and the sub carrier fix works that time :/

[Ryoandr]

Here is the SBCR trace on my VA4.


https://i.imgur.com/PpPNBu1.jpg
You can see it runs under all 3 colors, most notably under C25, C26, C27. It's also allowed to flow to ground at 2 points, at C29/R24 and C102.
The most surefire would be to cut the trace just after the via (under the ceramic disc capacitor)

Not sure what to do, maybe I just buy another Model 1 HDG MD and hope it's a VA2 and the sub carrier fix works that time :/

If you're in a PAL region (as you said it's a PAL VA4), you will not find a VA2 I believe. All I saw in PAL are VA4 and VA6, even with "high definition graphics - stereo sound" markings.

The upside is not having to worry about VA7s either

[ASDR]

Your picture doesn't load for me, Hm :/

But just going from your description, that's what I traced on my board as well, goes into the ground plane and below a bunch of caps close to the video encoder.

I cut the trace topside, was maybe a bit more fiddly.

Want to make an educated guess why this only changed and/or slightly improved my jail bars? I tried a different power supply (both original), all the electrolytic caps at least look good (no doming / leakage on the PCB) and I use a presumably quality CSync cable from RCG UK.

Mine has HDG + Ext Port. It certainly sounds friggin awesome to my ears! I can't hear any noise, distortion etc.

[Ryoandr]

put the link to image.
try forcing reload (hold shift and click reload icon or ctrl+F5)

Want to make an educated guess why this only changed and/or slightly improved my jail bars? I

A too thin trace cut can act like a capacitor, and a capacitor is transparent to AC, moreso for high frequency like the 3.57mhz subcarrier.

[ASDR]

I think I cut it pretty solid, dug it out a bit. Hard to take a picture of, but looks good under the magnifying glass

Do you think it's worth trying to cut it again on the underside to be extra sure? What about the other end, some people mentioned connecting pin 6 to ground?

[wgogh]

There are many "Mega Drive III" versions by Tectoy, one of them being based on Genesis 2. They later released the real Mega Drive III, and then re-released many times with different bizarre shapes. Now, they still releasing mega drive, but just emulation with sound and performance issues, which is sad. Idk if you guys are familiar with it, but Tectoy did a series of very bizarre Mega Drive editions over the years, one of them even had kind of a guitarhero guitar.

Anyway, surprised to see it ranked that high on the tests. Sadly, the sound sucks.

[bateman82]

I wasn't complaining about the article; it IS cool they did it. It's just that it seemed weird that MegaDrives performed so differently than the same Genesis models. Is there a link to the Sega16 thread? I'd read it.

My opinion on the X'eye is just what I feel. The first model Wondermega is just built so much better, and the plastic felt cheaper to me when I got the X'eye.

Sorry for my later reply, here's the link:

http://www.sega-16.com/forum/showthread ... m-bad-ones

My opinion on the X'eye is just what I feel. The first model Wondermega is just built so much better, and the plastic felt cheaper to me when I got the X'eye.

that makes sense, the Wondermega served as a high-end Mega Drive and Mega-CD unit, with built in S-Video and RCA audio output. four versions of the system were produced (some had Karaoke functions, others had Wireless controllers), although I've heard some (all?) of them don't support RGB without modification.

The first wondermega is my favourite Mega Drive "shape", so futuristic and cyberpunk.

No rgb output fot both japanese wondermega (1&2 same form as the x'eye), only via mod.

[FBX]

Made a screen grab of the blue channel in Artemio's color bar test pattern to show the difference between subcarrier cut on the VDP side and unmodded:



That's using the toggle switch on my VA2 Sega Genesis 1989 console.