complete DUO S-Video mod

[Tatsujin]

does someone know a guide for a complete s-video modification of the DUO?

i allready collected some pieces of information (rgb to s-video converter IC etc..) but never found a complete mod from the scratch to its working end.

here my researches about the CXA1645P IC with NTSC-circuit >  http://www.gamesx.com/rgbadd/cxa1645.pdf
do i need a TTL converter for the Pin 10? from where i will take the external clock?

thx in advance

tatsu

[herr-g]

I've never seen a complete guide and doubt it even exists for public.
As the PCE's video processor has no output for croma and luma you'll have to use a RGB => SVideo IC (like the one you ment above).

I know D-Lite has done it before (with the help of matt from gamesx) and even modded some PCEs for forum members. I suggest contacting D-Lite if he can hand you out a draft.
If you're gonna build it by yourself it would be great to publish it to Lawrence for the public.

Rgds
 herr-g

Btw. It's a damn mess that RGB is still such an alien in all those NTSC regions.

[grahf]

Tatsujin, you need an LM1881 sync seperator IC to get an imput for pin10. http://www.selectronic.fr/includes_selectronic/pdf/NS/LM1881.pdf
You then feed the composite video signal from the duo into that.

I already built my own circuit, using a smd cxa1645. However, I did not finish it. I still need to input the sine wave to pin 6. I could not find any solid information on what type of oscillator I needed to use, or how to use a crystal. I found a digital IC that is supposed to be a replacement for oscillators, but havnt tried it yet.

In any case, a writeup of this would not be hard. The hardest part is finding the cxa1645s in dip package.

[grahf]

I finally finished my CXA1645 based chroma encoder. I managed to squeeze the entire thing into a 4.5cm square project board. Video quality is EXCELLENT compared to the original composite video.

[Tatsujin]

wow, thx a lot for the pics grahf that's awesome!! may you have a complete shematic of your device to share?

[GUTS]

That's awesome, you should post that on Gamesx and get it added to their mods.

[Mortis]

That is indeed swell Boy do I wish I'd be able to see the difference in picture quality!

[Tatsujin]

it's almost like a RGB signal, but not that clear in matter of contrast and colors. but nearly almost.

[grahf]

I dont really have a schematic, I just worked off of the cxa1645 datasheet. I could have built it a lot easier If i used a bigger board.  If anyone has any questions about building their own, check aout the datasheet first, then feel free to ask.

[PCEngineHell]

Looks really good. If you decide to ever do another,do a step by step guide for building the encoder on here for people. Alot of people have problems with reading schematics but can go off of visual guides perfectly fine.

[grahf]

Thanks for the compliments guys. I just wish everyone could get to see a PCE with decent video   If only I knew where to get the CXA1645s in dip package (the bigger, through-hole ones). These surface mount ones are really hard to work with. On the sdm chip there are two pins of the chip for every hole on the project board. I just split each hole into two with a razor knife. Then removed the contacts on the next row to give myself some room. Also, I tried to arrange everthing so that it was small, and didnt use many jumper wires. If you dont care about this, it will make things easier.

I was thinking about just getting a custom PCB made if I decide to build another one. In the mean time, I may draw up some pictures that better explain what components have to go where on this encoder for those interested in tackling this as a project.

[kspiff]

To whoever eventually makes a schematic of this: you are my hero.

So is this mod pretty much as simple as providing the needed inputs as directed on the datasheet (not including the input from the crystal), then routing the output?  If so I may have to try this out.

I wonder if there would be room for the s-video mod, a region mod, and composite output (RCA) in a regular old US Turbo Grafx-16?  I guess I could always remove the RF modulator and some of the casing/shielding...

[grahf]

I'll start drawing up a simplistic schematic in paint shop when I have time. Its not really hard to build, but people without experience in reading datasheets might have a hard time knowing what type of components to use and such. I'll see if I can clear some things up.

[kspiff]

Any help you can offer would be appreciated.  In the meantime I'll try to figure things out myself and will make a schematic of my own.  If I can figure most of it out maybe you can look it over and help me make some corrections instead of having to make a schematic yourself.

And if anyone else is interested I made an offer of $13.95 for a CXA1645M from a seller on eBay (the only guy who is selling these chips right now) and he accepted, so if anyone else wants to try the same thing you can probably get the chip for $20 even shipped.

[GUTS]

That would be awesome, I was going to pay someone to do mine but Mike said it was a pain in the ass to do Duos so I'd actually like to try and build one myself as a challenge, the only thing I need is some instructions.

[kspiff]

I haven't finished yet but I've started on an attempt to make a schematic.  When I'm done I'll post it here so grahf can (maybe?) look it over and make advisements.

And while I'm posting can anyone recommend a resource that sells both the LM1881N and the ECS-2100AX @ 3.579545MHz (or a substitution for the LM1881N)?  I'm trying to avoid ordering the former from jameco and the latter (plus the other misc. parts) from mouser.

[kspiff]

OK.  Here is the first draft of what I would assume is the complete s-video conversion circuit.  I think I screwed up on one part (see NOTE) and should have shown vertical sync (pin 3 of the LM1881) routing to pin 10 of the CXA1645M instead of composite sync (pin 1 of the LM1881).  I left it as-is for now, though.

Can anyone confirm if this schematic appears to be laid out correctly?  grahf?

Thanks.

NOTE: Like the diagram says, I don't know if this is laid out correctly, DO NOT attempt to build this circuit as-is.

[grahf]

Kspiff, first of all welcome to the forum! Secondly, good job on the schematic. You saved me the trouble of finishing mine. As far as I can tell, everything is 100% correct. You did fine on the LM1881 also, the CXA1645 likes the composite sync input fine. The actual construction of this encoder isnt really hard, but its difficult to understand what goes where if your not familiar with electronics schematics and terminology. Plus, soldering to the SMD cxa1645s is a bitch. You really only need a few things:

cxa1645
Assorted ceramic caps.
Assorted electrolytic caps.
Assorted resistors.
The 3.579~ oscillator (makes the output of the chip NTSC).
LM1881 sync seperator (because the cxa1645 doesnt like the sync output from the HU6260 chip, so we strip a clean signal off of the composite video).

I made up a little elementary level chart for those who are unsure what the symbols on the schematic mean:

[kspiff]

Awesome.  I may have to try to get this built today then since I've nothing better to do (assuming the good electronics store downtown has LM1881s and proper crystals).  Once I test the build I'll take the "draft" markings off the schematic and maybe do a nice write-up in an HTML doc to send to gamesx.com.  Is there anyone else who needs to be credited besides you?  Did D-Lite help you, or anyone else?

I do have another question, though.  I was thinking I might get a real Duo soon (there is a sweet package on eBay ending soon I might splurge on) to replace my Turbo Grafx unit, at which point I'll order another CXA1645M so I can mod both... but before I order just 1 more chip would this mod work with other systems with the appropriate inputs available?  This seems to be a general purpose circuit and I was thinking it might be pretty sweet to put one of these in the ol' NES2, SNES mini, or Genesis1/CD/32X stack (well maybe not the latter since I'd probably have to mod all 3 units).  If so I'm also guessing I might not even need the LM1881 for some other systems...?

And thanks for the welcome, not sure if I'll end up being a big poster here but it's good to see an active board dedicated to the Turbo and its various incarnations.

[grahf]

No, nobody helped me at all. Most of my questions were answered by scouring over the GameSX board. Man that place is an invaluable resource. I owe a lot to that board.

This is a REALLY versatile chip, and yes, you may not need the sync seperator for other systems. Most of the FC Twins (snes clone + nes-on-a-chip) uses this chip stock, as well as playstions, saturns, and a number of other things. The genesis stuff usually has the older cxa1145 (which isnt so hot at svideo).

[GUTS]

That's awesome man, great job.  I'm going to build the RGB amp for mine but I think I'll add S-video also just for the hell of it after seeing your schematic, it looks like it would be fun to build.

[grahf]

GUTS, dont bother with the RGB amp if you plan on building this circuit. You can just tap RGB directly off the output of the cxa1645. It works great as a signal clamp, and from my understanding it will boost a weak signal as well. Try that first.

[termis]

Awesome guys.  This will be another project that I can try to tackle in the future.

[Tatsujin]

at that point, i would say you guys a big thanks for your big effort. it seems, that i struggled only with the external oscilators on pin 10 and pin 6. but now i can go ahead and bright up my picture to an acceptable quality, since i know it will work according grahfs researches

[CrackTiger]

Hey Keranu. This is a perfect thread to move to the new Turbo Mod section. 

[grahf]

Man, what a difference the picture makes. Its not perfect, but dot crawl is pretty much completely eliminated for me. You can tell immediatly in games such as Fray, where the textures in some of the towns turn into a disgusting mess with composite. Nice and stable with the svideo.

[CrackTiger]

Man, what a difference the picture makes. Its not perfect, but dot crawl is pretty much completely eliminated for me. You can tell immediatly in games such as Fray, where the textures in some of the towns turn into a disgusting mess with composite. Nice and stable with the svideo.

With S-Video on your Duo do see any faint vertical lines kinda like this?



The above image is an exaggeration, but I have a very faint version of those lines with my system.

[grahf]

No, none whatsoever.

[CrackTiger]

Oh well... maybe I'll get another PCE modded in the future or see if someone can fix the one I have. 

[kspiff]

Argh.  Another day without Turbo s-video goodness.  I accidentally picked up 0.001uF caps instead of 0.01.    I ordered some from mouser, but am hoping Fry's Electronics will have some when I stop by there this evening so I can be playing by this weekend.

I did however finish adding composite/RCA jacks (figured I may as well do both since s-video isn't very common), removing the RF hardware and putting the s-video jack in its place (which looks very nice and fits perfectly as long as you mount it upside-down -- otherwise the cable won't fit in properly because of the shape of the hole), and organizing the layout of the project board.  Would be nice to have something to cover the hole where the channel selector was but I can live with the one little imperfection.

Too bad I can't find a 8PDT switch to do a region mod though (other than a push on/off type that requires 2 5/8"+ clearance behind it, which I don't quite have).  And I was going to do an LED mod (thought it would look cool to have a blue LED shining from behind the Hu slot) but I'm starting to wonder if it would shine through the Hu slot gap enough to justify bothering with it. 

Oh, and does anybody know if I need to reattach the shielding to the PCB if I removed the RF unit?  Isn't RF interference the primary reason for the shielding?  I probably will put it back on anyways but if I can leave it off it would probably be easier to fit the project board in and reassemble everything.  Plus I pryed off several of the grounding pads and would have to use flux paste to attach the shielding to some new grounding points (which I'm not looking forward to ).

[grahf]

If it was my personal machine, I wouldnt bother with the shielding. The Duo-R doesnt have any shielding. (except on the bottom, but the top of the board with all the ICs is exposed. You can always do it later if for some strange reason you get interference, but its not likely.

[kspiff]

OK, thanks.  I think I'll just put the bottom shielding back on then.  There is a transistor which appears to be grounded through the shielding and I think it's screwed to the bottom half.

[kspiff]

Darn.  I tested my build a little while ago and it didn't work.  I'll have to go back in and double check everything I guess.  Seems odd since I was very careful and triple checked everything (wiring, continuity, etc.) before I installed.  Ah, well.  I just hope I really got the schematic right.

I wonder if it has something to do with grounding all the components to the PCB w/ one wire, or maybe 0.30 gauge kynar wire isn't thick enough for connecting the CXA1645 (I didn't use kynar for the grounds or input voltage to the CXA1645 or any of the other components though)?  Maybe I should have routed 2 separate grounds for the s-video plug instead of piggybacking them?  Hmm...

LOL it was fun ripping into the PCB and top shield with a dremel tool though (as it turns out I needed the carve out the spot where the RF unit was to get the s-video socket to fit with the case closed).

[grahf]

Your wire should be ok, these chips dont draw that much.  You can piggyback the svideo plugs no problem, its how mine (and everyone else) is done.

[kid_rondeau]

Hey guys,
for anyone who's building the S-video mod circuit, I just noticed something:

The schematic says that Pin 15 from the 1645 is Y-Out, and Pin 16 is C-out, but the data sheet for the CXA1645 has it the other way around.

What's the reason for this? When I first looked at the schematic I noticed something looked a bit strange, but I thought I just had to "flip it" because I was working behind the S-video jack.

Has anyone built the converter exactly as it is printed and had success?

[grahf]

Hey kid_rondeau, good eye.  I noticed on page 1 of the cxa1645 datasheet has it listed one way, but in the application circuits its listed opposite. kspiff, maybe this is your problem?

[kid_rondeau]

Oh man! Going over the data sheets in FURTHER detail, I see exactly what Grahf was talking about! Yeah man, I would be inclined to think that it's a typo in the application circuitry rather than on pages 1 and 4.

Grahf, I saw your pics you just posted of your successful mod, and just by looking it appears that you hooked it up with pin 15 as C-out and 16 as Y-out. Am I correct? It would be nice to set the record straight.

And while I have you here...
Am I going to need the "Sync" line for this circuit? Following the GameSX pinout diagram, I have seven leads hanging out of my TG-CD:

GND
+5V
Sync.
Red
Green
Blue
Composite Video


Following the S-Video schematic, I see no need for the Sync...is that for component video?

Thanks!

-Mike

[grahf]

I'm at work so I cant verify, but i'm 99% sure the first few pages of the datasheet are the correct ones, as this is the same pinout as the CXA2075 (which is a drop in replacement).

Yes you DO need sync signal (pin 10), but no, you wont be using the sync signal from the HU6260. The CXAs will take the weaker PC Engine RGB signals just fine, but people have reported trouble with the sync. Rather than building an amp, its easier to just use the LM1881 ic to strip a nice stable sync signal out of the composite video. Thats whats going on in the schematic.

[kspiff]

Ah, good eye.  I did make a typo.  Hmmm... I've got some time to kill this morning and if that works it would be an easy fix, I think I'll try right now and see if that was the problem.

EDIT: Nope.  That wasn't the only problem apparently.

[kid_rondeau]

I gotta tell ya,
I've been having a really fun time with this S-Video mod project. I majored in Electronics Tech at my college, but I always felt like I only had a textbook knowledge of the material, and was helpless when it came to circuit design.
But lately, I seem to be having a renaissance in all things electronic! And the camaraderie of these forums has only bolstered my resolve!

So, here's a quick update. After browsing data sheets for composite sync strippers, I've found that IC# EL1881CN is directly substitutable for the LM1881N, which I've had a difficult time locating from anyplace that doesn't have a minimum purchase. The EL1881CN is $1.94 from Mouser, and it's in stock.

My next task is to either find a good, close supplier for the Sony CXA1645/2075's, or else find a substitute for those.

When I get my TG-CD mod all finished and working, I'll post some pics!

[grahf]

Electronics are awesome Mouser is great for buying singles of things. Not the cheapest though, but you dont always need an entire strip or roll of something.

Kspiff, if you cant get your board figured out i'll be happy to take a look at it for you. Send me a PM if you get frustrated with it. You've got all the right parts, so its probably something simple thats being overlooked.

[kid_rondeau]

Oh, also, is it OK to use 1/8th Watt resistors throughout? I figured where space is an issue it makes sense. Also I assume 5WVDC is OK for all caps?

[grahf]

1/8th watt resistors will be fine. About the caps, small are ok for everything except for the VCC1 and VCC2 decoupling caps. I use 10v caps on these lines just for overkill, and because they're more common.  If you look at a factory board like a Playstation that uses this chip from the factory, most of the supporting caps/resistors are bare minimum (besides the fact that they are inherintly smaller due to being smd).

[SNKNostalgia]

I wonder if an AD742 would sub for the CXA chips? Of course all of the ones I have come across are the surface mounts. Oh well, save a mod set up for me Grahf heh. I will let you know when it is time. 

[grahf]

The AD724/AD725s do not work with the PCE for some reason. They also dont produce quite as good of a picture. The CXAs really are the best choice for this system.

[kid_rondeau]

Grahf,
I finally finished my S-video mod for my TG-CD, and it works...just not very well. The picture (color, clarity) is beautiful, but it's kind of wavy and jumpy. Any idea what this could be? I built the circuit per the diagram, and the only substitution I made was using the EL1881C for the LN1881 which I can't find.

[grahf]

I havn't tried the EL1881Cs yet personally, so unfortunatly I cant say. Its supposed to be a drop in replacement, so it SHOULD work fine.

Its hard to guess exactly what the problem is without seeing it in person.. It sounds like it could just be some interference. Double check the grounds, and also recheck the decoupling caps for VCC1 and 2 (make sure the polarity is correct on the electrolytic caps). Also, where are you getting your 5v from? If you look at the pic of my first board I posted on the first page, you can see that I pulled power from the middle of the board. There is a nice wide 5v plane which you can tap into.

Dont give up on it, you'll get it going eventually.

[kid_rondeau]

Whoa, thanks for the quick reply!

Here's an update:
I rechecked my connections and saw nothing flagrantly wrong, so just for the heck of it I tried the sync line on the expansion board in place of the stripped sync signal from the composite...YUCK!! It was dim and B/W and the vertical hold was off...I figured I'd have better luck if I went back to how I had it before, and retried.

I don't know what I did differently...maybe I just had a crappy connection from the 1881 before, but...

WOW!!!!

What an INCREDIBLE picture!! The first game I tried was Sidearms. No more weird "flashy" buildings in the first part of stage 1! And all the blues look so rich!

It is ALMOST completely stable as far as the picture is concerned. If you look VERY carefully, there is some periodic distortion about a third of the way up every few seconds. It's so minor, though, that I scarcely even notice...and I'm VERY picky about stuff like that.

Thanks for the encouragement!

[nat]

If you look VERY carefully, there is some periodic distortion about a third of the way up every few seconds.

Those are my Dark Lord powers affecting the planet's magnetic field. Don't worry about it.

[D-Lite]

The LM1881 is readily available in any quantity from Jameco if anyone needs them.  Both SOIC ($2.34 each) and DIP ($2.85 each).