complete DUO S-Video mod

[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 elementry 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

[Black Tiger]

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.

[Black Tiger]

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.

[Black Tiger]

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 ).