TurboGrafx-16 CD-ROM RGB mod woes

[Joe Redifer]

I am having trouble modding my Turbo for RGB.  I am using the expansion connector method with the CD unit, and I'm pretty sure I screwed up somewhere.  First question first:  I will be using an 8-pin DIN (stolen from a TurboTap) for the output and want it to have the same pinout as the Sega Genesis for the video.  The pinout reading on the Gamesx site does not say if I am looking at the male or female end, at least not anywhere I have seen.  So which is it?

Also, I gathered the correct parts and built the RGB amp.  Maybe we messed up somewhere, but I'm not 100% confident that it is non-working.  I don't get any signal when the amp is installed in the line (the screen does flicker when the power is turned on, but that's it).  When I bypass the amp all I get is an extremely weak BLUE signal.  Note that I am taking the RGB and routing it through an RGB to YUV component video converter so that doesn't mean I am neccesarilly looking at the blue output from the Turbo.  I could have wires crossed somewhere but again I am not 100% sure of that yet.  After messing around and connecting the R, G, B, and Sync lines to various random places on the output DIN, I can get a picture, but it is dark and the colors are wrong... there seems to be a huge lack of GREEN on the screen.  But what is on the screen is definitely not coming from the composite feed because the shimmering is gone when the games scroll and the pixels are much more defined as they would be in RGB.

Some more questions:

-Is it neccessary to have a +5v output from the RGB Amp or to hook the 5v line up to the output DIN in any way?

-What is the difference between Composite and composite sync?

-On the expansion connector method shown HERE it points out where composite video is.  Why?  Is it needed?  If I wanted composite video I wouldn't be taking it apart since the unit already provides that.  This confuses me slightly as to why this is pointed out.

Any other tips or even a demeaning rant would be appreciated!  Thanks!

[Joe Redifer]

Just as a reference, here's what my image looks like now:



It looks as if the white balance is off and everything is darker.  I can post pics of the amp but I'd be surprised if anyone could help just by looking at pictures of it.

[NFG]

A lot of monitors and most TVs will not function without a signal on the RGB plug that says "Yo, video here!"  You'll need to supply +5v for that reason.

As for your amp...  Something's buggered, but I'm not able to tell you what it is, sorry.

[viletim!]

Is this sega genesis RGB (SCART?) lead something you have bought or something you have made yourself?

[Joe Redifer]

I have the RGB SCART cable already.  I have many, actually. One for each of my systems except the friggin' NES which will forever live in composite land.  I took control port #5 from an old TurboTap peripheral to use as the 8-pin DIN.

[Guest]

I still have other questions:

-Is the diagram of the 8-pin din pinout for this:



Male or female?  It doesn't say.


-What is the difference between Composite and composite sync?

-On the expansion connector method shown HERE it points out where composite video is. Why? Is it needed? If I wanted composite video I wouldn't be taking it apart since the unit already provides that. This confuses me slightly as to why this is pointed out.

Thanks.

[FM-77]

1.
As you can see--the Mega Drive RGB cable contains resistors, so make your own PCE RGB cable or remove the resistors (should be in the SCART end). Also, make sure you fix the audio lines, otherwise you'll get mono sound on your PCE (lest you've got a Mega Drive II RGB cable).

2. Not sure. I have never used composite sync myself. Do you live in Europe? If so--use composite and not composite sync.

3. Composite video = video signal. With the R, G and B lines together with that (along with +5V and GND), it becomes RGB.



What you need to do is this:

1. Tap EVERYTHING from the AV port: R audio, L audio, GND, +5V and composite video.

2. Tap R, G and B from the video chip. Now you have eight wires -- this is ALL you need!

3. Connect a transistor to each line (the R, G and B lines that is)

4. Connect the other end of the transistor to your connector (and add in +5V there too).

5. Finish up your connector.

DONE!

[Joe Redifer]

I am in the US and use SCART RGB as a means to get the RGB video inside of my RGB to YUV converter to output component video.  I do not want composite video.  If I did I wouldn't bother going the RGB route.  Also the back of the CD unit has stereo outputs in addition to composite, so no need to tap the sound, either.

It would be a major pain to tap the RGB from the chip as that is inside the Turbo and I am working with the TurboGrafx CD unit.

Thanks for the diagram showing the resistors.  I will look into that, though I'm not sure why it would interfere with Turbo RGB if it doesn't interfere with Genesis RGB.

[viletim!]

Joe,
The SCART standard doesn't have a input for a TTL composite sync signal. Instead, the device with a SCART input is expected to strip the sync information off the composite video signal. That is why you need composite video going to your video converter. There's no reason to connect anything to the 'sync' pin as it's not going to be connected to anything in a SCART cable.

And Seldane is right, you will need to remove the junk from the inside of the genesis cable for it to work with your turbografx. It's probably a good idea to mark it as such because the cable will no longer work properly with a genesis after that.

[Joe Redifer]

Very interesting!  I have another SCART cable coming soon in the mail and I will dedicate that as the Turbo SCART cable and remove the resistors from that.

I guess I just have one final question (more of a clarification, really).

On the pinout listed in the picture below, I do NOT need to run a line from the sync, but rather from the composite?  Should this go into the SYNC side of the AMP I built as if it were the sync itself, or should it bypass the amp?



Thanks.

[viletim!]

Normaly you'd just connect the c-video output of the console to the c-video pin of the cable. I don't know the slightest thing about the turbografx's video outputs...it seems that the RGB at least is non-standard (requires an amp) so maybe it's safer to use the sync amp (which basicaly turns TTL sync into 'c-video style' sync).

[FM-77]

Like I said, you should be using composite video and not composite sync. Do not confuse this with composite video you use on your TV, because that's ONLY composite video. This is composite video + R, G and B, which is what RGB is.

If you look at the diagram I posted earlier, pin #3 on the Mega Drive RGB cable is composite video.

[Endymion]

I'm not sure why you are so confused about composite sync vs. composite video. Some monitors only need composite sync. This is the point labeled "sync" on the photo. The SCART spec on the other hand uses composite video and many of those televisions will not work properly if they are only fed sync. It's very nice if your equipment works with composite video, because then you do not have to make an LM1881 circuit to strip the sync from it, but if you get a rolling image on composite video then you will know that your monitor needs sync.

[Joe Redifer]

I'm confused about it because I'm not using a regular RGB monitor and am not the most educated when it comes to SCART.  But this thread is teaching me!

But now I am getting more confused...  Do I want to run a line from the pin that says "Comp video" from the picture I posted above, though the amp, and then to the composite video pin of the 8-pin DIN?  

What I planned on doing was running R, G, B, and sync through the amp and to their respective places on the DIN, and then running "comp video" straight from the pin to the DIN.  Would this not work?

Basically my question is what should go through the amp, Sync or "comp video", if either?

[NFG]

Typically console modding requires a lot of trial and error, because what we're doing a lot of the time has never been done before.  If there's no solid answers online and no one else knows the intimate details about your situation, you'll have to start trying things out and see what works.

Some monitors require composite sync, as they can't filter out the video (most monitors without TV tuners are like this, in my experience, thoguh in PAL territories that's not the case I hear).  Composite video is a more tightly defined standard than RGB and doesn't usually require an amp.  Composite sync is the one that would need an amp, if you decide to use it.

Soldering's easy and undoable.  Try it and see what happens, if it doesn't work try something else.

[Endymion]

What he said--it depends on your monitor. Maybe you could tell us what monitor you are using?

[Joe Redifer]

I'm using the best 20" TV I can find with component inputs.  It has a damn fine picture.  I am using the box pictured below to convert the RGB to component:


The tech spechs are:
Input Signal:
1 Scart - 1 Composite Video: 1 Vp-p 75 ohm / 1 RGB: 0.7 Vp-p 75 ohm

Output Signal:
3 RCA jacks - Y: 1 Vp-p 75 ohm, B-Y: 0.7 Vp-p 75ohm, R-Y: 0.7 Vp-p 75 ohm

It works great for my Genesis/SegaCD/32X, SNES, SMS, Neo-Geo, and Saturn.

[Joe Redifer]

Well I got it working, and it was indeed the composite sync.  However the picture is far too dark and I don't think my amp is working, so I bypassed it.

Is there anyone here whom I could pay to build a proper, working amp for the turbo?  Since I am using SCART, I don't think I need to boost the SYNC, just the RGB.  Any takers?  I'll pay for parts + time + shipping.

[FM-77]

All you need to do is to connect a transistor to the R, G and B lines--there's no need to build an amp. Unfortunately I don't know what kind of transistor you need as I didn't order them myself. I've tried to get this info but to no avail.

[viletim!]

Joe,
If the picture looks good, just lacking in contrast (and better than without the amp) then the amp is probably working. This type of amplifier (emitter follower cofiguration) doesn't actually have any voltage gain. It's purpose is to prevent the display device from loading the signal (all standard RGB inputs have a 75 ohm resistor connected between each video input and ground). One thing you might want to try is to short out the output coupling capacitor (220u) and replace the 75 ohm emitter resistor with something a bit higher - 470 ohms or even leave it out all together. Maybe try it on just one amp and see if that colour improves.

Seldane, you're just describing a super crude version of the amplifier he's already built.

[Joe Redifer]

With the amp in-line all I got onscreen looked like a very faint inverse shadow (black and white) of the image.  I assume it was getting this from the composite sync, which was not running through the amplifier.  There were 75ohm resistors on the RGB lines on the SCART cable, and it was suggested that I remove these and I did.  Are you suggesting putting something like 470ohm resistors back on those same lines?  Would that brighten the picture?

There is plenty of contrast, it is just too dark compared to the SNES, Genesis, Neo-Geo and Saturn RGB outputs I get.  I need a working amp.

[Joe Redifer]

Actually looking at the picture, it seems that ONLY the blues are too dark.  WTF?

[FM-77]

No! Do not add resistors to the R, G and B lines. I had the same problem as you and you can see that in this thread. I added resistors to the R, G and B lines because I thought that would solve my problem and it most certainly didn't.

What I had to do was add transistors to the R, G and B lines as described above and it now gives me a perfect, flawless RGB picture.

Edit: What I'm trying to say is that your amp is most likely not working.

[Guest]

Yeah I'm quite convinced that it is not working.

But what transistors?  The same ones in my amp (2SC1815)?  I can remove them and check them with the meter to make sure they work first.

Also the top of my screen bends slightly when it gets too bright (but only on the Turbo).  Should I add a transistor to the composite sync line?

[Joe Redifer]

I keep forgetting to input my name, so I finally registered.  

EDIT:  How would I add the transistor directly into the line since there are 3 connections?

[Endymion]

What I had to do was add transistors to the R, G and B lines as described above and it now gives me a perfect, flawless RGB picture.

Details? Your thread doesn't say what you did to remedy this. What transistor?

[Joe Redifer]

Well since nobody knows I will have to assume the following is the way it was done:

COLLECTOR = input
EMITTER = output
BASE = ground

I will hopefully do this in the next few days depending on how lazy I am.

[viletim!]

Code Select Expand


joe,
same conifig as the amplifier you've already built


.          + Vcc (+5v)
.          |
.          /c
.       b|/
.input---|
.        |\
.          >e
.          |
.          +----+ to TV



[Joe Redifer]

Interesting.  Thanks.

[Joe Redifer]

Alright, that did it!  Thank you all for helping me fill in the missing information.  It is kind of weird as the transistors take about 5 seconds after turning the power on to get up to the proper frequency and the onscreen effect is kind of... cool.  That's what the caps and resistors are on the amp to prevent, but otherwise I imagine it's the same.

I am amazed by the picture quality.  No more shimmering when games scroll.  


No more of this flickering hair, either!

Awesome!

For future information purposes, the transistors used are the same ones in the amp schematic on the Turbo RGB page.  They are NPN's.