Finally, RGB/VGA Mods

[movax]

As the topic says, I'm finally getting around to modding these consoles up to have a RGB connection (I'm not doing the GC & PS2 because my monitor already has component inputs ).

I did run into a few question though...I'll start with the N64. ('n64' is of course too short a query and 'n64 rgb mod' returned null).

From what I've gleaned off a few pages, firstly my console should be easily moddable (Release NTSC model). But from two sources (GameSX & mmonkey), it looks like:

1. Getting it off the chip, don't lift legs = possible too dark RGB
2. Getting off the chip, lift legs = possible too bright, interference RGB
3. Get it off three points on the bottom R8, R9, R10 = good RGB (I can only assume that these are before it passes through resistors C124(?)->C127.).

That's all good and swell for the RGB anyways though, but I notice a lack of... sync. I'm just conjecturing here that since this mod involves running to the multi-out jack I need to pick up a new A/V cable or rewire my existing one?


The Sega Saturn. I'm planning on grabbing a Model 2 from eBay and dropping in a chip to enjoy my deprived childhood now. Of course, I went to see if there was an A/V input on the wiki and low and behold: http://nfggames.com/wiki/doku.php=3fid=3dav:saturnav thar she blows.

I spy RGB and C Sync (which I think you can use a LMxxx something as part of a sync separator circuit), but will Saturn software output in this mode? I'm conjecturing that I can at least get S-Video out with no problems though, Pins 9, 10 and some ground on the board.


Ahh, mr. DC. I've pretty much got this mod down pat, but I just have some technical questions about it; mainly: http://www.raphnet.net/electronique/dreamc...ages/dricas.gif

1. That switch, "Enable VGA Mode" I think means either switch between 15kHz/31kHz output right? How does it do that? Either you run to ground through a 100pF cap, or you just run to ground, I assume that's the switch?

And is VGA "always on" (in the same vein as GC Component output)? In the case of a title that doesn't do VGA liek Bangai-O, will it happily also output S-Video as well? (I figure since I'm ripping open the thing I might as well put in a S-Video jack too eh).+?

2. Not really important, just wondering what exactly that IC does to the sync signals, some kinda tri-state buffer to either output 15/31 sync to the monitor?


Annnnnd lastly. What specification category do I need to take a look at to see if the monitor will accept 15/31 RGB. I'm not worried about the DC since it does "real" VGA (planning on that to LCD), but I have a Dell P1130 (Sony GDM-520 series chassis, a 21" monster) that I'm planning on using with the others. Should I be looking at sync frequencies or similar?

I plan on (re)compiling all these exploits so people can get a more recent look at modding these older consoles too, the more people that get into retro'ness the better. Hell, thanks to this site, I've got the schematic for SPDIF from my GC now...friggin' AWESOME!

*EDIT* Ok, so I've done my homework now...for the purposes of these discussions VGA indicates the 30kHz scan mode, not "oh look, you're using a VGa/Hd15 connector". That said, I assume the spec I want to look for is "Horizontal Scan Freq", and unfortunately, every monitor I won is minimum 30. Shit! At least the DC will be possible for now, once I get a 15kHz RGB monitor, I can hook up Saturn & N64 without problems, yeah? Or can a LCD display happily do scan freqs that low? LCD tech has really improved and I'm very proud of my S-IPS panel.

[blackevilweredragon]

i can answer the dreamcast question, as i have one..

the switch is run to ground...  When it's in VGA mode, it STAYS in VGA mode, nothing will get it out..  (though i've attempted in DC Linux to access 800x600, because in theory, the hardware can do this----but the mode results in a garbled VGA display)...

if a game will not run in VGA mode, the BIOS will say so, and fail to boot..  There is a plug connect trick, but it involves timing..

When in VGA mode, I believe the NTSC/PAL outputs are disabled---this i can't test, my VGA box has only VGA out..

EDIT:  My VGA box has NO IC for the sync signals, they go straight to the monitor.  the only thing on my boxes circuit is 3 caps, for R, G, and B..

[movax]

Hmm, ok, so that switch really is just a VGA ON/OFF (and with Off nothing gets out, not even 15khz RGB). Was a bit confused because on Raphnet, he indicated that the switch he has was for switching between NTSC and VGA sync freqs. Still wonder what the cap is there for.

Also, no IC in the box eh? Maybe that tri-state buffer is just there if you want sync freq switching capability. The 220uF caps make sense though of course to remove the DC Offset from the lines...

Also, on the GC digital audio mod, did some more research...I will begin examining the signal on my LeCroy LT344 DSO here at work so I can help others (others = people who aren't just in their sophomore year of college and actually have their EE degrees) figure out a circuit based on something other than the $40 TC9231N, preferably an American Cirrus part so I don't have to pay shipping.

*EDIT* I think I get the mode sel on the DC now, and I'll adjust the circuit accordingly...ground both 6/7 for VGA 30kHz, ground only 6 for RGB 15 kHz. I think I'll try ignoring that part of the circuit since I'm still unsure as to how having that 100pF cap helps.

[blackevilweredragon]

i think with no switch connection it's TV sync..  and one switch position is also TV sync, while the other is VGA sync..  i don't know the difference between the two TV syncs..

[Endymion]

Apparently there are two RGB types which are switchable. I have NO clue why they did this. But if they did something that weird it stands to conjecture that they could have two syncs as well. Not even SCART <-> Japanese RGB makes sense as that's all just a matter of where to tap and how it's wired up. I had hoped that some games which do not work in RGB but do work in VGA, or that some games which do not work in RGB but do work in TV modes, would have worked when using one of the two RGB modes, but they appear to be the same and the only way you can force it is to switch to VGA then back to RGB. So it shouldn't really make a diff which sync type you go with.

At least the DC will be possible for now, once I get a 15kHz RGB monitor, I can hook up Saturn & N64 without problems, yeah? Or can a LCD display happily do scan freqs that low?

Most do not, but there are some Samsung models that do. I have the Samsung 940MW and it's great. It even has a SCART connector! Supports sync on green as well. I think it is discontinued, but they're still available some stores and through ebay. Other multi-sync models from Samsung also have SCARTs on them, but you really should check. The 940MW was one of the best models that had this, the others were crappier or smaller screens, slower response times, etc.

[movax]

Yeah I think I'll just follow the diagram and switch to whichever one works (since those VGA Sel pins also are connected to pins on the tri-state buffer).

I found the ELM circuit thing for the RGB -> YPbPr converter (though the schematic has 'em listed as YCrCb out, shouldn't matter though, don't know how it'd output the digital model anyways), so I think I will build that with the LM1881N sync separator fed from C-Video (according to the circuit), a 74HC4053 to handle AC coupled RGB, and LM6172s as my mainstays opposed to the MAX4551s. I'll let you guys know how it goes.

I might get a JROK thing too, are those only the cost of shipping or something? Either way it's a lot less than paying $200 for a upconverter and I think I'll get better quality (my Gateway has component inputs ^_^).

[Segasonicfan]

I built Elm's converter with Viletim's help a while back.  Check the Arcade Work's section of my site if you want info and pics.  I also made a slightly improved schematic for the mod.

-Segasonicfan

[movax]

I built Elm's converter with Viletim's help a while back.  Check the Arcade Work's section of my site if you want info and pics.  I also made a slightly improved schematic for the mod.

-Segasonicfan

Yep, I used that thread as a reference a lot ^_^. And your site too...might I say that there is a FRIGGIN' SHIT TON OF SOLDER on that board @_@. Insane dude.

Still coming up with a bill-of-materials (I really really wished I lived near a parts warehouse), but I've decided a few things, mainly that I'm not building Elm's PSU unit (I'm using a 7.5V wall brick that's a Class 2 Transformer or so, so I'm just going to run that to the board with the "usual" power filtering there; 2 10uF caps and 1 .1uF for ripple, and then .1uF bypass caps to filter on the ICs.

I think I'll use the ICL7660 you had on your modded schematic definitely though, seems like the easiest way to generate VEE. Any other things/tips/tricks you noticed while building that thing?

The ICs I'm planning on using right now (before checking availability/having to switch to equivalents) are:

74HC4053, the Analog Multiplxer...just because al the RGB will probably be AC coupled, and even if it isn't..b.etter safe!

LM1881N - I assume this yoinks the sync out of the composite video signal, so every console I mod will always "need" composite video running to this; no big loss.

LM6172 - The mainstay of the circuit, I think I'll stick with these VFAs. The .1uF's should keep power real clean, might bump up to 1uF just because I have a bunch of those electro's around I think.

ICL7660 - To generate -5V, only needs two external capacitors.

Planning on mounting this all to ye olde breadboard and then enclosing in some metal shielding scavenged around. That leads me to my next question: What the hell to use for cabling from console -> this module? @_@ I'd think unshielded lengths of < 2" inside the console are ok, but how should I run 5 shielded wires to this module (assuming maximum 5, R, G, B, H/V Sync or C Sync depending on console)?

And on the Digital Audio front, started collecting data with my scope today on the GC, and it looks promising; should be able to build a circuit based on a cheaper Cirrus Logic part. I'll rip open a Wii next and look around for digital audio data on the board.  ^_^

I run all my audio through a receiver; I'm thinking about just purchasing a length of "RCA" wire (just coax I think, shielded) and some RCA solder jacks, jacket and such so I can chop up existing A/V cables, or install stress reliefs/RCA jacks at console end; anything to make connecting up easier. I am partial to the idea of using a DE9 custom pinout between all the consoles though; detachable = good.

[movax]

Hmm, new question

Would the ICL7660 provide enough output current to drive the 3 6172's? Looks like it only puts out .2A max. I'm thinking about either a 7.5V or 12V source feeding in (probably the former), and running the 7.5V -> ICL7660 -> LM7905 to get a smooth -5V output, since the 7660 will drop it by ~.5V under load, the 7905 should drop it to a clean -5. For the positive side, just running into a plain LM7805.

What should I do about cable shielding? In retrospect, maybe just putting a DE9 on each side and using a null-modem cable would work better than running 6 RCA cables for each console.

[viletim]

movax,
What's wrong with an ordinary mains transformer with a 12v centre tapped secondary winding? If you have only a single AC voltage available (like from an AC adaptor) then you can use a simple half wave rectifier to get your dual rails. Something like:

Code Select Expand

.   ------+-->|--+------|7805|----- +5v
. AC 9V   |      |+     \----/
.         |      C1       |
.   ---+  |      |        |
.      |  |      +--------+-GND
.      |  |
.      |  +--|<--+------|7905|----- -5v
.      |         |      \----/
.      |         C2       |
.      |         |+       |
.      +---------+--------+-GND

Also, have you ever cut open a game console RGB SCART cable? They almost always use unsheilded cable. Video lines have a relatively low impedance and are generaly not affected by stray electrical noise. In fact, more often than not they are a source of noise getting into the (relatively high impedance) audio lines. I think they require sheilding a far more than the video does.

[movax]

Yeah, I plan on using a 9V or 7.5V power brick (12V is a bit too much of a drop?), which provides DC +9V, right? Would that still work with that circuit up there (I see AC 9V going in; I'm not too familar with AC electronics).

Related to the above, where should I put the "big" smoothing caps to reduce ripple/noise from the transfomer, those Caps C1/C2 (10uF?) and add an additonal .1uF between +5V/GND to remove ripple?

And no, I'm in the US so I've never cut apart a SCART cable, but then again I really haven't cut up any of my console video cables, though I did nick one of my old N64 cables, and yeah...pretty thin shielding. Do you think it'd be fine to just run them unshielded (just bound together in some mesh/sleeving?).

[viletim]

The input needs to be AC (the -->|-- are diodes) so crack open your power brick and connect the output leads directly to the transformer. Either use a 9-12 VAC supply or a 12-15VDC unregulated supply (and bypass the filter/rectifier). C1/C2 should quite big, something like 1000� (though you should be able to get away with just 470� with a 12VAC input) and rated at least 25v.

And while I remember, you'll also need a capacitor between the output of the 7905 and ground, at least 10�. Put your .1� caramic caps next to the op-amps - where they are required.

If your cables are under 2m long then normal wire should be fine. You may get a buzzing noise in the audio (esp. when the video has lots of white) if you run it right next to your video signal. Experement at bit.

[Segasonicfan]

I used the 7660 because I like to use DC plugs with my adapters rather than building my own power transformers for projects.  Just a preference thing really.  I believe the circuit can handle up to 1A so it should be suitable.  Absolute worst case you could use a second one.

The excessive solder ground does a terrific job of shielding all the video data.  I have since put an additional grounding plate over the bottom as well.  The video output is simply astounding.

I recommend using the MAX chips like me and Viletim did.  They have an issue with using a too much power but they are much higher quality and will give you a better video signal.

the LM1881 is necessary for its back porch out.  It's used for the C sync too but the BP is why it is absolutely necessary as apposed to using an EL1883 IC.

As for ripple rejection you can see I always put a motherload of bypassing  caps on my projects.  It always helps and never really hurts.  I wouldnt recommend bumping the opamp ones to 1uf though as this wont do nearly as good of a job cleaning the power for the circuit.  Their current draw is very small and so .1uf is definitely way more effective.

-Segasonicfan

[movax]

Thanks for the replies guys;

viletim, yeah I'd prefer to use an intact power block like segasonicfan mentioned just so I can/could use it for other items too, which is why I was worried about the current draw a bit.

So the MAX (1441s IIRC, i'll look 'em up again...maybe I dyslexic'd those numbers) outperform the National LM parts? They are half the price too, which is nice. The pinout/diagram from the elm site adapts well to the MAX's then I guess (still +/- 5V etc), but how much more power do they draw? I know the LM7805 can provide up to an amp of VCC, but I think the 7660 can only do ~.1A (maybe 200mA) and it does a .5V drop too. Will that be enough to run 4 MAX's plus the analog multiplexer/sync separator? I don't know how much (if any) they draw on VEE compared to VCC.

And yeah, I'm currently writing out the BOM so I save on shipping from digi-key (ordering the caps in bulk, heh) so I'll stick with the .1uF's for ripple @ IC end, and use the 10 at the voltage regulators (the 7660 needs two of 'em for capacitor-charge pumping I think).

I was thinking about the wire thing; maybe I can find some preshielded multi-conductor wire already, but <2m eh? Hmm, I guess i can do that for the video.

For audio, I was thinking maybe converting to 2.5mm jacks on each side and using a shielded stereo cable to run audio; a bit smaller than running RCA.

BTW sega, did you get my PM about the Saturn?

[viletim]

movax,

The MAX4451s are not a suitable replacement for the LM6172 in this circuit. When I used them I found that when there was no input video input to the circuit (and hence no clamp signal form the LM1881) the MAX4451 on the input would bias itself a cause huge ammount of current to be wasted. I ended up having to put in an additional ciruit to pull on the inputs when there was no signal present.

I'd don't think the negative rail would draw more than 100mA though I don't really remember...I suppose I could measure it some time

[movax]

Hmm, ok so stick with the LM's then...

I think I'll find that ICL that puts out ~.2A from the input voltage since I'm just going to use a power jack to be safe. I'm thinking I have a 2A 7.5V supply at home (either that or a 9), and I'll do (positive) brick -> 7805 -> VCC (with a 10uF where needed...between line in and ground I think, and a 1uF ripple between +5V/GND IIRC), and brick -> ICL CMOS chip -> 7905 (handle the voltage drops) -> VEE, with the caps again.