Jamma Mega Drive - Picture is too dark

[GermanGameRoom]

Hello
I modded a Mega Drive to Jamma so I can play games like Mega Turrican on my Astro (tbh I'm still in the process, I still have to add the controls )
Power - works great
Sound - works great as well (it is able to be very loud, so not the typical problem everyone is having - I soldered the headphone jack so I can have the volume slider)
Picture - looks great with one complaint - it's darker than it should be even with the brightness cranked up completly

Here is a picture of the Astro running Sonic 1


(the Cab is still WIP so don't hate )

and here is a picture of the soldering on the PCB


green is green, blue is blue, red is red, yellow is sync and GND is elsewhere

does it have something to do with the ceramic capacitor?
The guide I followed didn't have an capacitor on the sync pin at all.

fyi I grabbed the signal at the DIN socket for scart RGB quality

I hope you guys can tell me what I have to do, to make it brighter

Thanks and have a nice day!

Edit: btw I also did a 50/60 Hz and a language mod to it and the cab didn't seem to like the 50Hz mode.. but it's fine with me because I will use 60Hz

[GermanGameRoom]

I removed the ceramic capacitor, but nothing has changed at all..

[GermanGameRoom]

Okay if nobody of you could tell me why this is because you haven't had a Jammadrive before, maybe you could throw in some thoughts or information on how this can happen?

I mean it's not a problem of my Monitor, because it runs my MVS on full brightness..

could it be because it's getting too high voltages? (wouldn't make sense to me, but yeah) because it is getting +12VDC instead of 10V, but when I tested it with the power brick the picture was dark as well..

Am I missing a capacitor or a resistor or something?

Could it be that is has something to do with the Sync?

Questions, questions.. I would be happy for anything you could tell me

[KmanSweden]

Don't some consoles need RGB amplifiers to boost signal from TV-friendly to Arcade monitor-friendly..?

[Porl]

Im a little unsure why your's could be pretty dark. When I made mine I didn't add any capacitors or resistors inbetween the solder point on the megadrive to the jamma fingerboard.

It looks like your doing a Megadrive 1? The 'drive I did was a megadrive 2. I thought I'd link to how my video is wired up to see if that helps at all. Once I'd figured the sync out ( I was getting horizontal blurring lines ) the image was nice and sharp and bright



Hopefully that helps a little

Porl''

[ninn]

The MegaDrive gives out Scart-Friendly signals. This [RGB-] signal peaks at 0,7V.
Your cab is JAMMA. This signal peaks at [needs reference, no warrenty] at 1V

That is why your picture is too dark, because it outputs a too low signal.

You need a booster / amplifier to get brightness right. On every single color-line.

I build a Jamma Mega Drive. On the NAC, I can push the brightness, to get it right - on my Blast, I can not boost brightness high enough, so the Jamma megadrive looks way too dark.
I would need such an amp too. Or a small circuit that does exactly that. and some spare time.

Hope that helped,
Ninn

[GermanGameRoom]

@Porl Yes this is a German (European) Mega Drive 1 and I'm guessing that is has something to do with the Sync as well.. but I haven't found the answer yet.. some people who built it as well had similar problems.. wavy pictures and stuff and no one could tell 100% if this one is the right Sync or the lowest one.

@ninn: this seems to make sense, but I haven't seen anyone doing it and I've even seen pictures of one with an Astro City using it without any extra components..
Have you built one from a MD1 or MD2? Have you used the same pinouts as I am doing? Could you like me an Amp that you think would help me?

I've replaced the original LED with a way brighter green one.. I hope this doesn't suck to much juice

[cthulhu]

I made one from a European Megadrive 1 and never had any problems with the picture.

[GermanGameRoom]

I made one from a European Megadrive 1 and never had any problems with the picture.

I made it after I've seen the following tutorial and copied what he has done..
would you check if you have made anything else than the dude in the tut?

http://www.jammaplus.co.uk/forum/forum_ ... a-md-jamma"

the +5VDC from the pinout is for the Audio, right? (I used the headphone jack audio)

[ninn]

Every proper RGB modded console will be too dark on a jamma system.
The TV and the Cab expect different signal strengths. It is easy as that.

If you cab can compensate with the brightness, thats great and will look fine.
But that does not change the fact that the Signal your Megadrive is outputting is weak [jamma] signal.

Nothing wrong with your cab or the megadrive. It is just like that.


There are lots of amps available. Some are easy to build yourself from a few components, others are ICs that just need some voltage and done.


I just worked on MegaDrive 1s, all regions. Every megadrive i modded showed the signs you describe.
I am pretty sure I soldered the R,G,B-wires directly to the fingerboard too. Dont think i did fancy stuff there.

[ninn]

hm ... just had a look at your screenshot.

What puzzles me is the over-saturated colors. If I am not wrong, this is not how it should look like. Never been a great sonic fan.

But I remember a talk I had with user Mendel, where he showed some pictures of his jamma megadrive, which gave him trouble. He had very oversaturated colors, that just looked wrong at second sight. He fixed the oversaturated colors with a hackboard of 3 caps and 3 resistors. I never understood why the colors became oversaturated at his cab. Maybe a talk with him, or the builder of his jammadrive may help you too.

[GermanGameRoom]

hm ... just had a look at your screenshot.

What puzzles me is the over-saturated colors. If I am not wrong, this is not how it should look like. Never been a great sonic fan.

But I remember a talk I had with user Mendel, where he showed some pictures of his jamma megadrive, which gave him trouble. He had very oversaturated colors, that just looked wrong at second sight. He fixed the oversaturated colors with a hackboard of 3 caps and 3 resistors. I never understood why the colors became oversaturated at his cab. Maybe a talk with him, or the builder of his jammadrive may help you too.

I see what you are referring to, but the picture on my Cab isn't oversaturated, it's just on the picture I made of it.. It's made with my crappy phone camera

Everything with the picture is fine, except the brightness.. I mean as you probably can see it isn't unplayable but it's quite darker than it should be.
I play my Neo Geo games on highest brightness from my cabinet (from the potentiometers in the front)

would it be possible to fix it, by playing with the potentiometers on my monitor? So the brightness for my neo geo games would be kind of low to mid and mega drive would be all the way?

I hope that made some kind of sense.. I just remembered it while I was typing, that I should be able to adjust the brightness from the back of the cab as well.

[cthulhu]

I've just checked my JammaDrive because it's been year since I've used it. It also has a picture that's slightly too dark, but turning up the brightness works just fine with my New Astro. Just tweak the pot settings and I think you'll be fine.

[GermanGameRoom]

I will keep you guys updated as soon as I will fix it (or as soon as I play with the pottis and it doesn't seem to work)
I will take a rest for the next couple of days^^

[GermanGameRoom]

My rest is over and I am still facing the same problems..
I could have sworn that someone told me one day that you can adjust the brightness directly on the chassis as well and not only through the front..

So I just would have turned it up on the chassis and I could change it from the front when I'm playing Neo Geo or Mega Drive..

But after researching I only found an "ABL" knob which stands for Auto Brightness Limiter and what I found out it should only change how bright the monitor will get until the chassis will dimm it when there is a lot of white on the screen..

can anyone confirm the ABL part?
can anyone confirm the fact that there is no brightness adjustment on the chassis?
can anyone send me a specific link to an Amp from which ninn was talking about?

Thanks in advance

[GermanGameRoom]

Push*

still hoping on answers

[Asure]

You do not have a remote adjustment board under the control panel of your cabinet? My astro has brightness there (as well as other stuff for r/g/b..)

[GermanGameRoom]

You do not have a remote adjustment board under the control panel of your cabinet? My astro has brightness there (as well as other stuff for r/g/b..)

It has but like I said before it is cranked all the way up and still the picture from my Mega Drive is too dark
(cranked all up is the perfect setting for my arcade PCBs)

[Porl]

I've just wondered, have you tried building an RGB amp? I've seen one when following the PC Engine Scart mod on Mmmonkey's site. I don't think I did it in the end because mine looked absolutely fine when used on my TV's.

Here is a link to the page. I don't see why this wouldn't work as its just a simple amp that sits on the RGB lines : http://www.mmmonkey.co.uk/pc-engine-rgb-amp/

It's weird because I've been using my Jammadrive on my arcade machine and leaving the RGB pots tuned for my CPS2 / jamma games has left the brightness looking nice. It's quite confusing how your's is dark


Porl''

[GermanGameRoom]

I've just wondered, have you tried building an RGB amp? I've seen one when following the PC Engine Scart mod on Mmmonkey's site. I don't think I did it in the end because mine looked absolutely fine when used on my TV's.

Here is a link to the page. I don't see why this wouldn't work as its just a simple amp that sits on the RGB lines : http://www.mmmonkey.co.uk/pc-engine-rgb-amp/

It's weird because I've been using my Jammadrive on my arcade machine and leaving the RGB pots tuned for my CPS2 / jamma games has left the brightness looking nice. It's quite confusing how your's is dark


Porl''

Thanks your link may help me with my problem, I havent found it with google..

I tried turning up the contrast which made it brighter and it was as bright as I wanted it to get but the contrast was too high (as expected)..
I will take a closer look at the tutorial at your link tomorrow because I'm drunk right now