complete DUO S-Video mod

[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.