CDX RGB fix!

[Segasonicfan]

Anyone out there with a CDX and a good RGB monitor knows that the RGB signal it outputs is unusable garbage.  Mine shows up on my PVM2530 with distorting lines and and dark image (the distorting lines being the major problem of course).  Well, I've been tinkering with my CDX today and have discovered a way to get MUCH better RGB out of this sucker:



This is the best place to solder the RGB lines from (they are located on the ends of the highlighted resistors).  It seems the MB3514 is given some very low-level RGB signals because those original lines are fed through a resistor and an improper value of capacitance before the MB3514 gets a hold of and clamps them.  Thus, the output is trash because it doesn't have the pure originating signal to work with.  That's my theory anyway.



This is where I traced the RGB lines to their origins.  As you can see, they come directly out from the main CPU and theres even tiny pads there to solder to.  I recommend using the other locations though.

Now after feeding these lines to my PVM, I get a terrific image but not quite perfect:



The colors aren't quite as vibrant as they should be.  I've tried the standard 75ohm and 220uf values but they haven't really helped.  I only got this decent image after I connected 75ohms between the lines actually (terminating 75ohms to ground didn't work either).  I'm sure with more tinkering the values could be figured out but the main thing here is that there actually is a good image to work with

Here's what it should look like with perfect RGB (this is from my Gen3 RGB out):


-Segasonicfan

[Endymion]

Nice work.

[GZeus]

if only you had an occiloscope...
Then you could see what's different between the two and how to fix it...

[Segasonicfan]

A little update...I've found that when I feed the signals through the PSOne LCD (with its RGB buffer) the output is perfect.  I think all that needs to be done is variable impedance matching for each line.  I need to order more pots to test it out but I will keep everyone posted

-Segasonicfan

[Segasonicfan]

Okay, I think I got this all figured out now.  When fed through the PSOne LCD and pulled out again I get a pretty much perfect image:



I found a datasheet for the circuit that the RGB inputs and outputs from...it's  a EL5410CR which  is just a quad op amp.  So it seems the signals although bright enough, are not amped enough in the CDX which is why they don't work with the MB3514 clamping.  

Anyway, I'm gonna mark this one up as a success since all you need is a quad op amp and these solder points to get perfect RGB from a CDX ^_^

-Segasonicfan  

[NFG]

Damned good work!  Now whip up a circuit for us to add to the wiki, yes?  =)

[viletim!]

There's a MB3514 encoding the video inside my Mega Drive and it's RGB output is fine. If the composite video output is ok and the RGB isn't (with the usual resistor/cap in series) then you might just have a faulty IC.

[Segasonicfan]

Viletim- this is actually a problem with all CDXs and not the chroma encoder at all.  It's a problem with the CDX's RGB output being fed into the MB3514 or similar IC.  I actually replaced my MB3514 with a BH7236AF (a CXA2075 clone) but the RGB output is still terrible.  I think this proves that it isn't a malfunctioning IC that is the problem, but a unique difference between the CDX and all other Mega Drive/Genesis RGB signals.  Also to note, the Sega chip that generated the RGB is a 315-5660, so if that chip is present in any other Sega system with good RGB output (via a chroma encoder), than I would be wrong.  But as far as I know it's unique to the CDX/Multi-Mega

Lawrence- I will definitely whip up a circuit for ya once I build it seperate from the PSOne LCD.  I'm not sure if I have any quad opamps in my parts at the moment so I may have to order some.  It shall be done though

-Segasonicfan  

[Segasonicfan]

Okay, I finally finished all the work for the finest CDX RGB possible ^_^  Here's the end result:





Not only is the RGB properly colored and illuminated but I think I discovered how to fix the noisy video as well.  It seems the 0.1uf caps between the MB3514 and RGB inputs have degraded over time and need replacing.  I'm not sure if replacing them would work to fix the composite video noise (will try it later) but it sure makes a big difference when using RGB.

Now onto the mod...

The RGB coming straight from the CPU is too strong to connect straight to the op amps.  They feed through 4.7k resistors and then onto the 0.1uf caps before they reach the MB3514.  Simply tap the RGB after the 4.7k resistors but before the 0.1uf caps here:



After that they must be sent (along with the sync line) through 4 opamps.  this can be done easily with the EL5410 found in the PSOne LCD or similar opamps like the LM324 (haven't built the circuit yet to test quality but it's the same).  Both are single supply quad op amps which are easiest for the mod.  Here's the circuit(s):



Pretty simple really  FINALLY some great RGB from the CDX!

-Segasonicfan

[Segasonicfan]

I replaced the 0.1uf caps and it worked  greatly reduces the noise in all video (composite, S-video).  Here are the locations to replace:



-Segasonicfan

[Segasonicfan]

I guess nobody cares about this anymore.... :/  No point in posting any more info then..

-Segasonicfan

[NFG]

Bah!  I was waiting for the conclusions with baited breath.

I mean, I post mods for navi Saturns, which NO ONE will ever use.  YOu can finish this!  =)

[Segasonicfan]

Bah! I was waiting for the conclusions with baited breath.

I mean, I post mods for navi Saturns, which NO ONE will ever use. YOu can finish this! =)

but it is finished....I posted the circuit like you requested and I put up pics of the perfect video output and the fix for video noise :/  Here's the finished install:



The mod won't work with a quad op amp like the LM324, I'm not sure EXACTLY why because I don't know crap about opamps but I'm sure it's not too hard to figure out.  Works perfect with the EL5410.

-Segasonicfan

[Computolio]

   I'd do this but I'm deathly afraid of opening my CDX. They're just too delicate and expensive.

   It's good knowing that the noise is fixable, though! You should put this on the wiki.

[NFG]

Sorry Segasonicfan, I guess the massive images you used made it too hard for my lazy ass to actually read all of what you wrote.  I was waiting for the end of the story and it turns out I just needed to scroll the screen right!  =D

[Segasonicfan]

It's good knowing that the noise is fixable, though! You should put this on the wiki

Yeah, the video fix makes a Big difference.  Put any of this on the wiki and I will be very happy.  Hell, I'd even put it on the wiki for ya Lawrence.  I've always wanted to contribute to the main page  Also, you ever gonna add CDX import jumpers to the wiki?  I snapped some shots of it and it would be a great addition to the Genesis import mod section.

Sorry Segasonicfan, I guess the massive images you used made it too hard for my lazy ass to actually read all of what you wrote. I was waiting for the end of the story and it turns out I just needed to scroll the screen right! =D

Heh, sorry the screens were so big, I just wanted to make sure the tiny stuff was clear enough for everyone to see.  I'll have to link it next time or something.

-Segasonicfan

[mr. newbie]

thanks for the pictures. i love seeing what rgb looks like. i want to kiss your montior.

[RGB32E]

SSF,

From what you've posted with your CDX/PVM2530 combo, I'm wondering if there is a revision difference between CDXs (ie. Neo Geo AES).  I have a CDX/PVM2030, and did not encounter any of the stated issues.  For all of the 9-pin mini din genies (X'Eye, Genesis 2, and CDX) I've only had to put 220uf caps on the RGB and Sync, and resistors on the RGB lines (75 ohm or less).  This is also true for a friends PVM2530.  Hmmm....?

And, from my experience, its better to use a 75 ohm resistor for blue, 68 ohm resistor for green, and a 62 ohm resistor for red... that way, the signal will compensate for the PVMs high color temp (9300K and "New Dynamic Color" settings).  The result is a lot more colorful picture, no modding/hackery involved!

Cool job though....

[Segasonicfan]

very odd...maybe the 2030 has better compatibility?  My CDX RGB always worked with my PSOne LCD but the noise was always very bad.  I think the fact that amping it worked on my 2530 also proves that the signals are too weak.  So even if your RGB works the amp and/or cap fix will give you a much better picture.

-Segasonicfan

[RGB32E]

Well.... without caps on the RGBS, I don't get a stable picture and colors are transposed.  Without resistors, the RGB signals are too strong.  From the various RGB enconder IC data sheets I've seen, the RGB, YC and composite output signals are always filtered with a cap and resistor...

Have you even tried other CDXs to see if there is something wrong with the unit you own?  Are you sure you are not chasing red herrings?  :unsure:

Once I get a hold of a digital camera, I'll take some shots from my setup (with Sonic 2 title screen!)  The first picture you posted looked very sharp, but the signal looks too strong (especially blue video).  While the other pictures may look more colorful and not washed out, they also look blurry (might be the camera shot?).  Ehh....  

The 2030 and 2530 are cut from the same cloth (so to speak).  So I can't see how there would be any compatibility differences between the two models from the same family.  I've built RGB cables for most all of the systems out there (that don't need RGB mods) for both models (20/2530) and have not encountered compat differences.

Finally, adding/replacing the RGB circuitry is the LAST thing I'd want to do to any of my systems that have great output to begin with.  Don't forget the quality of your cable construction.... it makes a significant difference in picture quality!

[NFG]

Yay, digging up old threads!

Hey, Segasonicfan, a lot of your images have expired.  Do you still have them?

I'm in a Sega mood and I'm looking into fixing the RGB on my CDX units.  Finally.

[Segasonicfan]

Wow, oooooold thread haha.  Unfortunately if its not linked then I probably deleted it years ago.  But you can check photobucket.com/segasonicfan to see what shows up- I've tried to keep it more updated and organized without removing things in recent years.

Also note, the CDX outputs perfect RGB stock.  This unit did have an issue that was later resolved.  So you can do an encoder upgrade and some power supply modifications for cleaner output, but there is no need to amplify the signals already present.

-Segasonicfan

[NFG]

Ah, thanks for that.  I'll have a look.

I have two CDX units and they're both completely shit in the RGB department.  Do you have links for these other mods? 

[Segasonicfan]

Yeah (sorry just saw your thread today)- I have links and pics on my website: freewebs.com/vgmods.  Under "Sega Genesis Modifications" at the bottom of the page I show the 0.1uf ceramic caps that the RGB feeds through.  Sometimes these go bad and make for a shitty output.

Note: The opamp stage I made was to compensate for a shitty encoder I put in my CDX back in the day.  It is unnecessary in a stock CDX.

Other than that there really isn't much to blame except the stock MB3514 encoder (which I doubt is bad).  The RGB goes from the 315-5660 ASIC through a 0.1uf ceramic cap each and then into the encoder.  The encoder buffers the output and sends it straight to the A/V port.

So if that doesn't work I'd guess you are having power board issues.  I've seen those power caps start to go bad more.  Anyway, If that doesn't help you fix it I'd be more than happy to take a look and repair it for ya for free.  Especially since your website is what got me soldering to begin with, some 13 years ago

and as I should have asked first: what is shitty about the RGB?   The stock system does get a fair amount of interference on solid colors, due partly to the VDP + YAMAHA + other stuff being integrated into one chip (the 315-5660).  Installing a 7805 for the video encoder seems to help with this, as well as isolating the power line to the 315-5864.

-Segasonicfan

P.S. when I put "www" before my website, my post vanished... Is there a hyperlink block on here?

[NFG]

There's no blocking going on, I suspect you've done something else wrong.  If it happens again, let me know (better, leave the post alone and link it to me via private message) and I'll sort it out.