Unstable image JP Dreamcast & JP Megadrive JVC BMH2000PND

[MK75]

https://ibb.co/fak9iQ
https://ibb.co/gh5Ock
https://ibb.co/gRgh3Q

Hi guys, I hope you can help as I don't really know where to begin with this.

I'm new to the world of broadcast monitors for gaming and recently bought a JVC BM-H2000PND for my Japanese Megadrive and Japanese Dreamcast.

I believe I have made the right connections at the back ( see photos ) and whilst my Megadrive is holding a steady image, it looks all green and weird and my Dreamcast colours look amazing but the screen is unstable and continually moves side to side.

The Dreamcast image is that of Capcom vs SNK 2
The Megadrive image is that of Strider

I can confirm that RGB is selected and the sync button pressed.

The monitor was working fine with a RGB Euro Scart on another system and both consoles mentioned above work fine (albeit looking a bit rubbish) on my LCD which the JVC is replacing.

Any ideas? I have tried searching but don't really know what to look up.

Many thanks in advance.

Mike

[Fudoh]

From my understand all the termination switches (those on the three RGB inputs as well as on the sync input) belong in the 75ohm position (= toggled to the right).

(and the obvious of course: make sure your adapterr cable runs into the right direction. Scart to BNC is not the same as BNC to Scart)

[MK75]

Thanks. Just tried switching the 4 switches to 75ohm position and it made the Megadrive look a bit better but not how it should.

And Dreamcast worse.

When it comes to the adapter, what do you mean, correct direction?

[Fudoh]

When it comes to the adapter, what do you mean, correct direction?

The DC picture obvious looks like sync was missing. On a Scart to BNC cable the BNC sync cable is supposed to be connected to pin 20. On a BNC to Scart cable the BNC sync cable is supposed to be connected to pin 19 instead.

Doesn't explain why the MD displays an image at all, but worth checking.

[theclaw]

I don't have the specs of your particular monitor. It may require SDI formatted video, but unlikely since it's showing something.

Anyhow AFAIK raw Megadrive or Dreamcast RGB output is not intended for TV use. They're supposed to have appropriate resistors/capacitors inside the cable.

[MK75]

If we stick to the DC first as having two systems not working only confuses matters.

The DC is JP.

I fitted a PAL PSU to it so that I didn't have to use a step down converter.

Other than that, it is untouched. I'm using a regular SCART lead which normally displays correctly on my LCD.

Would it have anything to do with JP21 / Euros Scart?

[theclaw]

Trying to plug a JP21 cable into a SCART adapter or monitor won't work right. A different pin layout.
But JP21 is rarely used outside Asia. Except with specialty devices like XRGB.

To my knowledge Sega only released a domestic JP21 cable for Saturn. (despite the regular Master System, Megadrive, and DC each having RGB outputs of course)

[MK75]

Okay. So my best course of action is to check the pin outs on my scart cable, when I looked there was no pins missing like on a composite cable.

[Fudoh]

If your RGB cables work fine on another display, you don't have to check.

But if you haven't used your Scart to BNC breakout cable before on another display, you should check that one. As said, these aren't bi-directional, so maybe you got one with the wrong direction. Just unscrew the scart connector and check where the sync line connects to.

[MK75]

Hi.

Thanks all so far, seems like we are getting to the bottom of what might be happening here.

Just popped open the two casings on the respective scarts.

Have tried getting the best possible angles.

Firstly the pin outs on the Dreamcast cable

https://ibb.co/dxt8tQ https://ibb.co/j5HOSk

And two pictures of the pin out of the BNC cable

https://ibb.co/dtTf7k/ https://ibb.co/jraSnk

What's clear is that there are more pins connected to the Dreamcast Scart than that of the BNC cable so I can understand why the two might not marry up when connected together through the adjoining female adapter.

Thanks in advance

[Crayfish]

My current best guess on this going by the symptoms is that the megadrive is actually sending composite thru scart, not rpg. I have a snes cable that does this. It might explain why there is a stable image even when MK75 turn off/ un plugs the extrenal sync.
One of these would tell you (you would also need a composite cable with a single bnc adapter for the yellow video:
http://www.ebay.co.uk/itm/SCART-Adaptor ... SwI3RW8k-M
But that would be good money after bad to just test if it is composite.

Retro Gaming cables do a MD RGB scart cable, but I dont know if there ones can be used with JP model MD. Anyone?
https://www.retrogamingcables.co.uk/sega/mega-drive-1


The Dreamcast must be outputting RPG down its scart cable, as the colors are correct, but the sync is wired up to the wrong pin for that scart to bnc breakout cable (which is wired for euroscart). Maybe he needs a JP21 to Euroscart adapter? The opposite of this:
https://www.retrogamingcables.co.uk/aud ... -converter

Look up the pinout diagrams for jp21 / JP-Dreamcasr scart / Euro Scart to compare.

[MK75]

Cheers Cray. Lots to digest.

The scart I am using on the JP Megadrive is one of those you mentioned.

A specialist RGB cable with a separate audio lead for the headphone jack.

[Fudoh]

The pictures look alright. The DC RGB cable is fine (except for the that the audio ground pin isn't wired).

The Scart to BNC cable is also correct, but it relies on the video ground pin (17) to be connected, which isn't the case with all RGB cables. It's a still weird to use a Scart to BNC breakout cable with a male scart header and then plug a coupler into it. You would usually go for one with a female connector from the start.

Now the real question is what your coupler does. If it correctly cross-connects pins 19 to 20 (and 20 to 19) and if all the ground wires are connected to each other.

You could check if you can open up the fem/fem coupler to check the connections. If not your best guess would likely be to get a better breakout cable.

[MK75]

Inside the FEM/FEM adaptor.

https://ibb.co/h1uMFF

Obviously it don't look good but I don't know if this might have happened when I unpopped the block or if it was causing the problem all along.

What does that brown wire represent.?

[Crayfish]

Fudoh what do u think about the MD outputting composite theory? It displays the same image for MK75 whether he has snyc plugged in or not with the Megadrive.


If the cross-connect pins 19 to 20 (and 20 to 19) was an issue, and MK75 is unable to tell for himself by looking, would running through a (RGB capable FM to FM) scart switcher solve / isolate this?
It would be good to get a scart switcher anyway, because you are running multiple inputs, and this will save continually plugging and unplugging.
This one is only £7 and is the one I am currently using:
http://www.ebay.co.uk/itm/SCART-SWITCHE ... o-SU4WIucw
Or there is this one that comes highly recomended by some of the RGP people on youtube Ive seen:
http://www.ebay.co.uk/itm/Bandridge-SVB ... SwNnRYfSSf


Btw, what effect will the audio ground pin the DC cable have if its not connected?

[Fudoh]

Fudoh what do u think about the MD outputting composite theory?

sync and composite video share a line, so no. This wouldn't affect the RGB pins.

Btw, what effect will the audio ground pin the DC cable have if its not connected?

that depends on what he's doing with the audio and how he's grabbing it from the Scart output.

@MK75: maybe you could mark where the pointy edge of the Scart connector connects to, so we can get a sense of direction on that image.

[MK75]

@Fudoh

Pointy edge? I don't quite understand what you mean?

[MK75]

@Crayfish

I have ordered one of those multi scart switchers you mentioned. Makes sense.

[Fudoh]

Isn't one edge of the scart connector pointy? Am I using the wrong term?

The lose cable would be the GREEN channel if I'm seeing it right. The cross connection between 19 and 20 seems to be ok as well.

My next guess would be a continuity problem on the ground line. If you have some spare wire. Connect the outer edge of the sync BNC connector to one of the pins where you know GND to be present.

[MK75]

https://ibb.co/gqXp2v

Is that the pointy bit?

The loose wire is BROWN

[Fudoh]

The loose wire is BROWN

I know, but it's the wire carrying the GREEN signal.

[MK75]

Ahhh. Okay.

I see what you mean Fudoh.

[Crayfish]

Seems strange that the DC colors are correct if the Green signal was broken?

Also i just did a google search on dreamcast to pvm and it says there are actually issues from game to game and the system is problematic overall. This guy seems to have exactly the same problem:

https://www.reddit.com/r/gamecollecting ... m_display/


Perhaps it is best to focus on getting the megadrive working first, because these issues seem to be to do with the DC output itself. Explains why there are 2 different problems.

[MK75]

Seems I am not alone then. Thank you Crayfish.

Well I have ordered the switcher, the RGB Megadrive scart is brand new and works with the LCD I was using.

What are the chances my MD is not outputting RGB?

If it wasn't, would I get any image from it at all when connecting the system to the JVC?

[MK75]

If the MD wasn't RGB enabled say, and I connected it to the broadcast monitor via a RGB scart, what do you think the output would be?

Green screen? No screen? Other?

[Fudoh]

Also i just did a google search on dreamcast to pvm and it says there are actually issues from game to game and the system is problematic overall. This guy seems to have exactly the same problem:

his problem is that the grounds don't connect. Most DC RGB cables don't have ground connected at all (except for the outer shielding) and when the Scart to BNC breakout adapter expect GND on a different pin you end with a result like this.

Hence my suggestion to just bridge ground externally for testing.

[Crayfish]

So will a scart switcher address the GND issue, or is it something MK75 needs to do himself?
Are all switchers wired up in the way to correct this issue (this one is RGB)? They are all just pass throughs correct?

Also, the people in that thread mention issues outside GND with the DC:

"Some games support SCART, some support VGA, the union of both supports all games it's believed...The dreamcast is quite an annoying system to get RGB out of with 100% compatibility."

Also MK can u fully describe the MD symptoms again. Plugging and unplugging the sync / turning external sync button on -off has no effect on the picture correct? It holds stable whatever. That is why I suspected it is not RGB coming through the cable, as you can send non RGB composite etc thru a scart and your tv would recognize it.
Maybe do a little research into JP Megadrives out puts, cables etc

[theclaw]

Also MK can u fully describe the MD symptoms again. Plugging and unplugging the sync / turning external sync button on -off has no effect on the picture correct? It holds stable whatever. That is why I suspected it is not RGB coming through the cable, as you can send non RGB composite etc thru a scart and your tv would recognize it.
Maybe do a little research into JP Megadrives out puts, cables etc

JP MD1 and MD2 definitely have RGB outputs. It's required for the 32X to work.

You're right scart cables may be exclusively composite video.

[MK75]

So I went ahead and bought a some RCA to BNC adapters and stuck one on the composite cable ( yellow video ) for each the Dreamcast and the Megadrive.

First up. The JP DC running in composite with video A pressed on the monitor.

https://ibb.co/bCieLF

And then the Megadrive

https://ibb.co/j3Dznv

Okay so it's composite but at least the image is stable, the colours are right and I can now play my games.

[Fudoh]

Maybe the JVC doesn't accept composite as sync for RGB signals. In this case you would need a breakout cable with a stripper built into it. You would need to check with another JVC user to verify this.